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Allergies, also known as allergic diseases, are a number of conditions caused by
hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. They are usually referred to as an over-reaction of the immune sy ...
of the
immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biolog ...
to typically harmless substances in the environment. These diseases include
hay fever Allergic rhinitis, also known as hay fever, is a type of rhinitis, inflammation in the nose which occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose, sneezing, red, itchy, and wate ...
, food allergies,
atopic dermatitis Atopic dermatitis (AD), also known as atopic eczema, is a long-term type of inflammation of the skin (dermatitis Dermatitis (also known as eczema) is inflammation of the skin Skin is the layer of usually soft, flexible outer tissue coveri ...

atopic dermatitis
,
allergic asthma Asthma is a chronic (medicine), long-term inflammation, inflammatory disease of the bronchi, airways of the lungs. It is characterized by variable and recurring symptoms, reversible Airway obstruction, airflow obstruction, and easily triggered b ...
, and
anaphylaxis Anaphylaxis is a serious allergic reaction Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reac ...
. Symptoms may include red eyes, an itchy rash,
sneezing A sneeze, or sternutation, is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucous membrane, mucosa. A sneeze expels air forcibly from the mouth an ...
, a
runny nose Rhinorrhea or rhinorrhoea is the free discharge of a thin nasal mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also origi ...
,
shortness of breath Shortness of breath (SOB), also known as dyspnea (BrE British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificati ...
, or swelling.
Food intolerances Food intolerance is a detrimental reaction, often delayed, to a food, beverage, food additive, or compound found in foods that produces symptoms in one or more body organs and systems, but generally refers to reactions other than food allergy. Foo ...
and
food poisoning Foodborne illness (also foodborne disease and colloquially referred to as food poisoning) is any Disease, illness resulting from the spoilage of food contaminant, contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food, ...
are separate conditions. Common
allergen An allergen is a type of antigen In immunology, an antigen (Ag) is a molecule or molecular structure, such as may be present on the outside of a pathogen, that can be bound by an antigen-specific antibody or B-cell antigen receptor. The pr ...
s include
pollen Pollen Tube Diagram Pollen is a powdery substance consisting of pollen grains which are microsporophytes of seed plants The spermatophytes, also known as phanerogams (taxon Phanerogamae) or phaenogams (taxon Phaenogamae), comprise those plan ...

pollen
and certain foods. Metals and other substances may also cause problems. Food,
insect sting Insect bites and stings occur when an insect Insects (from Latin ') are pancrustacean Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exos ...
s, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves
immunoglobulin E antibodies Image:Allergy degranulation processes 01.svg, Degranulation processes 1: antigen; 2: IgE antibody; 3: FcεRI receptor; 4: preformed mediators (histamine, proteases, chemokines, heparin); 5: granules; 6: mast cell; 7: newly formed mediators (prosta ...
(IgE), part of the body's immune system, binding to an allergen and then to a receptor on
mast cell#REDIRECT Mast cell A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem ...

mast cell
s or
basophil Basophils are a type of white blood cell. Basophils are the least common type of granulocyte, representing about 0.5% to 1% of circulating white blood cells. However, they are the largest type of granulocyte. They are responsible for inflammato ...

basophil
s where it triggers the release of inflammatory chemicals such as
histamine Histamine is an organic nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele a ...

histamine
. Diagnosis is typically based on a person's
medical history The medical history, case history, or anamnesis (from Greek: ἀνά, ''aná'', "open", and μνήσις, ''mnesis'', "memory") of a patient A patient is any recipient of health care Health care, health-care, or healthcare is the maintenance ...
. Further testing of the
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biolo ...
or blood may be useful in certain cases. Positive tests, however, may not mean there is a significant allergy to the substance in question. Early exposure to potential allergens may be protective. Treatments for allergies include the avoidance of known allergens and the use of medications such as
steroids , a steroid with 27 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations ...
and
antihistamines Antihistamines are pharmaceutical drug, drugs which treat allergic rhinitis and other allergies. Typically people take antihistamines as an inexpensive, Generic drug, generic, over-the-counter drug that can provide relief from nasal congestion, ...
. In severe reactions injectable
adrenaline Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate p ...

adrenaline
(epinephrine) is recommended.
Allergen immunotherapy Allergen immunotherapy, also known as desensitization or hypo-sensitization, is a medical treatment for environmental allergies Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity Hypersensitivi ...
, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites. Its use in food allergies is unclear. Allergies are common. In the developed world, about 20% of people are affected by
allergic rhinitis Allergic rhinitis, of which the seasonal type is called hay fever, is a type of rhinitis, inflammation in the nose that occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose, sneezing ...
, about 6% of people have at least one food allergy, and about 20% have
atopic dermatitis Atopic dermatitis (AD), also known as atopic eczema, is a long-term type of inflammation of the skin (dermatitis Dermatitis (also known as eczema) is inflammation of the skin Skin is the layer of usually soft, flexible outer tissue coveri ...

atopic dermatitis
at some point in time. Depending on the country about 1–18% of people have asthma. Anaphylaxis occurs in between 0.05–2% of people. Rates of many allergic diseases appear to be increasing. The word "allergy" was first used by Clemens von Pirquet in 1906.


Signs and symptoms

Many allergens such as dust or pollen are airborne particles. In these cases, symptoms arise in areas in contact with air, such as eyes, nose, and lungs. For instance,
allergic rhinitis Allergic rhinitis, of which the seasonal type is called hay fever, is a type of rhinitis, inflammation in the nose that occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose, sneezing ...
, also known as hay fever, causes irritation of the nose, sneezing, itching, and redness of the eyes. Inhaled allergens can also lead to increased production of
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body and covers the surface of internal organs. It consists of one or more layers ...
in the
lung The lungs are the primary organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma ...

lung
s,
shortness of breath Shortness of breath (SOB), also known as dyspnea (BrE British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificati ...
, coughing, and wheezing. Aside from these ambient allergens, allergic reactions can result from
food Food is any substance consumed to provide nutritional Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organism In biology, an organism (from Anci ...

food
s,
insect stings Insects or Insecta (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power ...
, and reactions to
medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, therapy, treat, or preventive medicine, prevent disease. Drug therapy (pharmacotherapy) ...

medication
s like
aspirin Aspirin, also known as acetylsalicylic acid (ASA), is a medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug Uncoated tablets, consisting of about 90% acetylsalicy ...

aspirin
and
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
s such as
penicillin Penicillins (P, PCN or PEN) are a group of originally obtained from ' s, principally ' and '. Most penicillins in clinical use are chemically synthesised from naturally-produced penicillins. A number of natural penicillins have been discov ...

penicillin
. Symptoms of food allergy include
abdominal pain Abdominal pain, also known as a stomach ache, is a symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than ...
,
bloating Abdominal bloating is a symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered bloo ...
, vomiting,
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery defecation, bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration of ...
,
itch ITCH is a HECT domain In molecular biology, the HECT domain is a protein domain found in ubiquitin-protein ligases. The name HECT comes from 'Homologous to the E6-AP Carboxyl Terminus'. Proteins containing this domain at the C terminus include ubiq ...

itch
y skin, and . Food allergies rarely cause
respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system A biological system is a complex biological network, network which connects several biologically relevant entities. Biological organization spans sever ...

respiratory
(asthmatic) reactions, or
rhinitis Rhinitis, also known as coryza, is irritation and inflammation of the mucous membrane inside the nose A nose is a protuberance in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multic ...
. Insect stings, food,
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
s, and certain medicines may produce a systemic allergic response that is also called
anaphylaxis Anaphylaxis is a serious allergic reaction Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reac ...
; multiple organ systems can be affected, including the
digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anus which includes all the organs of th ...

digestive system
, the
respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertainment, and media * ''Network'' (1976 film), a 1976 Ame ...

respiratory system
, and the
circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex biological network, network which connects several biologically ...
. Depending on the rate of severity, anaphylaxis can include skin reactions, bronchoconstriction, ,
low blood pressure Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dia ...
,
coma A coma is a deep state of prolonged unconsciousness Unconsciousness is a state which occurs when the ability to maintain an consciousness, awareness of self and environment is lost. It involves a complete, or near-complete, lack of responsive ...
, and
death Death is the permanent, irreversible cessation of all biological functions that sustain a living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objects and dead organi ...

death
. This type of reaction can be triggered suddenly, or the onset can be delayed. The nature of
anaphylaxis Anaphylaxis is a serious allergic reaction Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reac ...
is such that the reaction can seem to be subsiding, but may recur throughout a period of time.


Skin

Substances that come into contact with the skin, such as
latex Latex is a stable dispersion (emulsion An emulsion is a mixture of two or more liquids that are normally Miscibility, immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class o ...

latex
, are also common causes of allergic reactions, known as
contact dermatitis Contact dermatitis is a type of inflammation of the skin. Some symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, and swelling. The rash isn't contagious or life-threatening, but it can be very uncomfortabl ...

contact dermatitis
or eczema. Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a " weal and flare" reaction characteristic of hives and angioedema. With insect stings a large local reaction may occur (an area of skin redness greater than 10 cm in size). It can last one to two days. This reaction may also occur after
immunotherapy Immunotherapy or biological therapy is the treatment of disease by activating or suppressing the immune system. Immunotherapies designed to elicit or amplify an immune response are classified as activation immunotherapies, while immunotherapies ...
.


Cause

Risk factors for allergy can be placed in two general categories, namely
host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host (19 ...
and
environmental A biophysical environment is a life, biotic and Abiotic component, abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environ ...

environmental
factors. Host factors include
heredity Heredity, also called inheritance or biological inheritance, is the passing on of traits Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for str ...

heredity
,
sex Sex is either of two divisions, typically male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot sexual r ...
, race, and age, with heredity being by far the most significant. However, there have been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in exposure to
infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the infectious agents and the toxins they produce. An inf ...
s during early childhood, environmental
pollution Pollution is the introduction of s into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). s, the components of po ...

pollution
, allergen levels, and
dietary In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the ...
changes.


Foods

A wide variety of foods can cause allergic reactions, but 90% of allergic responses to foods are caused by cow's
milk Milk is a nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animal Animals (also called Metazoa) are multicellular eukaryotic organisms that ...

milk
,
soy The soybean or soya bean (''Glycine max'') is a species of legume native to East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, ...
,
eggs Eggs are laid by female animals of many different species, including bird egg, birds, reptiles, amphibians, a few monotreme, mammals, and fish, and many of these have been eaten by humans for thousands of years. Bird and reptile eggs consist o ...
,
wheat Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'' ...

wheat
,
peanut The peanut, also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), and as ''Arachis hypogaea'', is a grown mainly for its edible . It is widely grown in the and subtropics, being important to both small and large comme ...

peanut
s, tree nuts,
fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct related groups. Around 99% of living fish species are ray-finned fish, belonging to the class , with over 95 ...

fish
, and
shellfish Shellfish is a colloquial and fisheries Fishery is the enterprise of raising or harvesting fish and other aquatic life. Commercial fisheries include wild fisheries and Fish farming, fish farms, both in fresh water (about 10% of all catch) and t ...

shellfish
. Other food allergies, affecting less than 1 person per 10,000 population, may be considered "rare". The use of hydrolysed milk
baby formula Infant formula, baby formula or just formula (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United St ...
versus standard milk baby formula does not appear to change the risk. The most common food allergy in the US population is a sensitivity to
crustacea Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Eua ...

crustacea
. Although peanut allergies are notorious for their severity, peanut allergies are not the most common food allergy in adults or children. Severe or life-threatening reactions may be triggered by other allergens, and are more common when combined with asthma. Rates of allergies differ between adults and children.
Peanut The peanut, also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), and taxonomically classified as ''Arachis hypogaea'', is a legume A legume () is a plant Plants are predominantly photosynthetic Photosynth ...

Peanut
allergies can sometimes be outgrown by children. Egg allergies affect one to two percent of children but are outgrown by about two-thirds of children by the age of 5. The sensitivity is usually to proteins in the white, rather than the
yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example beca ...

yolk
. Milk-protein allergies are most common in children. Approximately 60% of milk-protein reactions are
immunoglobulin E Immunoglobulin E (IgE) is a type of antibody An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and Viral dis ...
-mediated, with the remaining usually attributable to inflammation of the colon. Some people are unable to tolerate milk from goats or sheep as well as from cows, and many are also unable to tolerate
dairy A dairy is a business enterprise Business is the activity of making one's living or making money by producing or buying and selling products (such as goods and services). Simply put, it is "any activity or enterprise entered into for profi ...

dairy
products such as cheese. Roughly 10% of children with a milk allergy will have a reaction to
beef Beef is the culinary nameCulinary names, menu names, or kitchen names are names of foods used in the preparation or selling of food, as opposed to their names in agriculture Agriculture is the science, art and practice of cultivating pl ...

beef
. Beef contains small amounts of proteins that are present in greater abundance in cow's milk.
Lactose intolerance Lactose intolerance is a common condition caused by a decreased ability to digest lactose, a sugar found in dairy products. Those affected vary in the amount of lactose they can tolerate before symptoms develop. Symptoms may include abdominal pa ...
, a common reaction to milk, is not a form of allergy at all, but rather due to the absence of an
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates in ...

enzyme
in the
digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syst ...
. Those with tree nut allergies may be allergic to one or to many tree nuts, including pecans,
pistachios The pistachio (, ''Pistacia vera''), a member of the cashew family, is a small tree originating from Central Asia Central Asia is a region in Asia which stretches from the Caspian Sea in the west to China and Mongolia in the east, and from A ...

pistachios
, pine nuts, and walnuts. Also
seeds A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, it was released to generally positi ...

seeds
, including
sesame seeds Sesame ( or ; ''Sesamum indicum'') is a flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to ...
and
poppy seed Poppy seed is an oilseed Vegetable oils, or vegetable fats, are oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that ...

poppy seed
s, contain oils in which protein is present, which may elicit an allergic reaction. Allergens can be transferred from one food to another through
genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the direct manipulation of an organism's gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_in ...
; however genetic modification can also remove allergens. Little research has been done on the natural variation of allergen concentrations in unmodified crops.


Latex

Latex Latex is a stable dispersion (emulsion An emulsion is a mixture of two or more liquids that are normally Miscibility, immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class o ...

Latex
can trigger an IgE-mediated cutaneous, respiratory, and systemic reaction. The prevalence of latex allergy in the general population is believed to be less than one percent. In a hospital study, 1 in 800 surgical patients (0.125 percent) reported latex sensitivity, although the sensitivity among healthcare workers is higher, between seven and ten percent. Researchers attribute this higher level to the exposure of healthcare workers to areas with significant airborne latex allergens, such as operating rooms, intensive-care units, and dental suites. These latex-rich environments may sensitize healthcare workers who regularly inhale allergenic proteins. The most prevalent response to latex is an allergic contact dermatitis, a delayed hypersensitive reaction appearing as dry, crusted lesions. This reaction usually lasts 48–96 hours. Sweating or rubbing the area under the glove aggravates the lesions, possibly leading to ulcerations.
Anaphylactic Anaphylaxis is a serious allergic reaction that is rapid in onset and may cause death. It typically causes more than one of the following: an itchy rash, throat or tongue swelling, shortness of breath Shortness of breath (SOB), also known as dy ...
reactions occur most often in sensitive patients who have been exposed to a surgeon's latex gloves during abdominal surgery, but other
mucosal A mucous membrane or mucosa is a membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions ...
exposures, such as dental procedures, can also produce systemic reactions. Latex and banana sensitivity may cross-react. Furthermore, those with latex allergy may also have sensitivities to avocado, kiwifruit, and chestnut. These people often have
perioral In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...
itching and local
urticaria Hives, also known as urticaria, is a kind of skin rash A rash is a change of the human skin which affects its color, appearance, or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to ...

urticaria
. Only occasionally have these food-induced allergies induced systemic responses. Researchers suspect that the cross-reactivity of latex with banana, avocado, kiwifruit, and chestnut occurs because latex proteins are structurally homologous with some other plant proteins.


Medications

About 10% of people report that they are allergic to
penicillin Penicillins (P, PCN or PEN) are a group of originally obtained from ' s, principally ' and '. Most penicillins in clinical use are chemically synthesised from naturally-produced penicillins. A number of natural penicillins have been discov ...

penicillin
; however, 90% turn out not to be. Serious allergies only occur in about 0.03%.


Insect stings

Typically,
insects Insects (from Latin ') are pancrustacean Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, Thorax (ins ...

insects
which generate allergic responses are either stinging insects (
wasps A wasp is any insect Insects (from Latin ') are pancrustacean Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-p ...

wasps
,
bees Bees are flying insects closely related to wasps and ants, known for their role in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyly, monophyletic lineage within the ...

bees
,
hornets Hornets (insects in the genus ''Vespa'') are the largest of the Eusociality, eusocial wasps, and are similar in appearance to their close relatives yellowjackets. Some species can reach up to in length. They are distinguished from other Vespinae ...
and
ants Ants are eusocial Eusociality (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is ...

ants
) or biting insects (
mosquitoes A mosquito is any member of a group of about 3,500 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defin ...

mosquitoes
,
ticks Ticks (suborder Ixodida) are parasitic arachnid Arachnida () is a Class (biology), class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes orders containing spiders (the largest order), sco ...
). Stinging insects inject venom into their victims, whilst biting insects normally introduce
anti-coagulants Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquito A mosqu ...
.


Toxins interacting with proteins

Another non-food protein reaction,
urushiol-induced contact dermatitis Urushiol-induced contact dermatitis (also called Toxicodendron dermatitis or Rhus dermatitis) is a type of allergic contact dermatitis caused by the oil urushiol found in various plants, most notably species of the genus ''Toxicodendron'': poison ...
, originates after contact with , ,
western poison oak ''Toxicodendron diversilobum'' (syn. ''Rhus diversiloba''), commonly named Pacific poison oak or western poison oak, is a woody vine or shrub in the sumac family, Anacardiaceae. It is widely distributed in western North America, inhabiting conife ...
, or poison sumac.
Urushiol Urushiol is an oily mixture of organic compounds with Allergic contact dermatitis, allergenic properties found in plants of the Family (biology), family Anacardiaceae, especially ''Toxicodendron'' ''spp.'' (e.g., poison oak, Toxicodendron vernici ...

Urushiol
, which is not itself a protein, acts as a
haptenHaptens are small molecules that elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself (in general, only large molecules, infectious agents, ...

hapten
and chemically reacts with, binds to, and changes the shape of
integral membrane protein An integral membrane protein (IMP) is a type of membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Int ...
s on exposed skin cells. The immune system does not recognize the affected cells as normal parts of the body, causing a
T-cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system, and play a central role in the adaptive immune response. T cells can be easily distinguished from other lymphocytes by the presence of a T- ...
-mediated
immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, Parasitism, parasites, and Fungus, ...

immune response
. Of these poisonous plants, sumac is the most virulent. The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling,
papule A papule is a small, well-defined bump in the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal cove ...
s,
vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features of ...
,
blister A blister is a small pocket of body fluid (lymph, Serum (blood), serum, Plasma (blood), plasma, blood, or pus) within the Epidermis, upper layers of the skin, usually caused by forceful rubbing (friction), burning, freezing, chemical exposure or ...

blister
s, and streaking. Estimates vary on the percentage of the population that will have an immune system response. Approximately 25 percent of the population will have a strong allergic response to urushiol. In general, approximately 80 percent to 90 percent of adults will develop a rash if they are exposed to of purified urushiol, but some people are so sensitive that it takes only a molecular trace on the skin to initiate an allergic reaction.


Genetics

Allergic diseases are strongly :
identical twins Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of TwinLast Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two emb ...
are likely to have the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in non-identical twins. Allergic parents are more likely to have allergic children, and those children's allergies are likely to be more severe than those in children of non-allergic parents. Some allergies, however, are not consistent along
genealogies Genealogy (from el, γενεαλογία ' "the making of a pedigree") is the study of families, family history, and the tracing of their lineages. Genealogists use oral interviews, historical records, genetic analysis, and other records to ob ...

genealogies
; parents who are allergic to
peanut The peanut, also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), and as ''Arachis hypogaea'', is a grown mainly for its edible . It is widely grown in the and subtropics, being important to both small and large comme ...

peanut
s may have children who are allergic to
ragweed Ragweeds are flowering plants in the genus ''Ambrosia'' in the aster family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to m ...

ragweed
. It seems that the likelihood of developing allergies is and related to an irregularity in the immune system, but the specific
allergen An allergen is a type of antigen In immunology, an antigen (Ag) is a molecule or molecular structure, such as may be present on the outside of a pathogen, that can be bound by an antigen-specific antibody or B-cell antigen receptor. The pr ...
is not. The risk of allergic
sensitization Sensitization is a non-associative learning process in which repeated administration of a stimulus results in the progressive amplification of a response. Sensitization often is characterized by an enhancement of response to a whole class of sti ...
and the development of allergies varies with age, with young children most at risk. Several studies have shown that IgE levels are highest in childhood and fall rapidly between the ages of 10 and 30 years. The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 10.
Ethnicity An ethnic group or ethnicity is a grouping of people who identity (social science), identify with each other on the basis of shared attributes that distinguish them from other groups. Those attributes can include common sets of traditions, ancest ...
may play a role in some allergies; however, racial factors have been difficult to separate from environmental influences and changes due to
migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum len ...

migration
. It has been suggested that different genetic loci are responsible for asthma, to be specific, in people of
European European, or Europeans, may refer to: In general * ''European'', an adjective referring to something of, from, or related to Europe ** Ethnic groups in Europe ** Demographics of Europe ** European cuisine, the cuisines of Europe and other Western ...
,
Hispanic The term ''Hispanic'' ( es, hispano) refers to people, cultures Culture () is an umbrella term which encompasses the social behavior Social behavior is behavior Behavior (American English) or behaviour (British English; American and B ...
,
Asian Asian may refer to: * Items from or related to the continent of Asia: ** Asian people, people in or descending from Asia ** Asian culture, the culture of the people from Asia ** Asian cuisine, food based on the style of food of the people from Asi ...
, and
African African(s) may refer to: * Anything from or pertaining to the continent of Africa: ** People who are native to Africa, descendants of natives of Africa, or individuals who trace their ancestry to indigenous inhabitants of Africa *** Ethnic groups ...
origins.


Hygiene hypothesis

Allergic diseases are caused by inappropriate immunological responses to harmless
antigens In immunology Immunology is a branch of biology that covers the study of immune systems in all organisms. Immunology charts, measures, and contextualizes the Physiology, physiological functioning of the immune system in states of both health ...
driven by a
TH2 The T helper cells (Th cells), also known as CD4+ cells or CD4-positive cells, are a type of that play an important role in the , particularly in the . As their name suggests, they "help" the activity of other immune cells by releasing , small ...
-mediated immune response. Many
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
and
virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecu ...

virus
es elicit a TH1-mediated immune response, which down-regulates TH2 responses. The first proposed mechanism of action of the hygiene hypothesis was that insufficient stimulation of the TH1 arm of the immune system leads to an overactive TH2 arm, which in turn leads to allergic disease. In other words, individuals living in too sterile an environment are not exposed to enough pathogens to keep the immune system busy. Since our bodies evolved to deal with a certain level of such pathogens, when they are not exposed to this level, the immune system will attack harmless antigens and thus normally benign microbial objects—like pollen—will trigger an immune response. The hygiene hypothesis was developed to explain the observation that
hay fever Allergic rhinitis, also known as hay fever, is a type of rhinitis, inflammation in the nose which occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose, sneezing, red, itchy, and wate ...
and
eczema Dermatitis is of the , typically characterized by iness, and a . In cases of short duration, there may be small s, while in long-term cases the skin may become . The area of skin involved can vary from small to covering the entire body. Derma ...

eczema
, both allergic diseases, were less common in children from larger families, which were, it is presumed, exposed to more infectious agents through their siblings, than in children from families with only one child. The hygiene hypothesis has been extensively investigated by immunologists and
epidemiologists Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in defined population In biology, a population is a number of all the organisms of the same group ...
and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that have been seen since
industrialization Factories, refineries, mines, and agribusiness are all elements of industrialisation Industrialisation ( alternatively spelled industrialization) is the period of social and economic change that transforms a human group from an agrarian societ ...
, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents. Epidemiological data support the hygiene hypothesis. Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world. Longitudinal studies in the third world demonstrate an increase in immunological disorders as a country grows more affluent and, it is presumed, cleaner. The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases. The use of antibacterial cleaning products has also been associated with higher incidence of
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
, as has birth by
Caesarean section Caesarean section, also known as C-section, or caesarean delivery, is the surgical procedure Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical or dental s ...
rather than vaginal birth.


Stress

Chronic stress can aggravate allergic conditions. This has been attributed to a T helper 2 (TH2)-predominant response driven by suppression of
interleukin 12 Interleukin 12 (IL-12) is an interleukin Interleukins (ILs) are a group of cytokines (secreted proteins and signal molecules) that were first seen to be expressed by white blood cell White blood cells (WBCs), also called leukocytes or leu ...
by both the
autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The autonomic nervous ...

autonomic nervous system
and the
hypothalamic–pituitary–adrenal axis The hypothalamic–pituitary–adrenal axis (HPA axis or HTPA axis) is a complex set of direct influences and feedback Feedback occurs when outputs of a system are routed back as inputs as part of a Signal chain (signal processing chain), chai ...
. Stress management in highly susceptible individuals may improve symptoms.


Other environmental factors

There are differences between countries in the number of individuals within a population having allergies. Allergic diseases are more common in
industrialized Industrialisation Industrialisation (or industrialization) is the period of social and economic change that transforms a human group from an agrarian society An agrarian society, or agricultural society, is any community whose economy is based ...

industrialized
countries than in countries that are more traditional or
agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors such as watching tele ...

agricultural
, and there is a higher rate of allergic disease in
urban Urban means "related to a city". In that sense, the term may refer to: * Urban area, geographical area distinct from rural areas * Urban culture, the culture of towns and cities. Urban may also refer to: General * Urban (name), a list of people ...
populations versus
rural In general, a rural area or a countryside is a geographic area that is located outside town A town is a . Towns are generally larger than s and smaller than , though the criteria to distinguish between them vary considerably in differen ...

rural
populations, although these differences are becoming less defined. Historically, the trees planted in urban areas were predominantly male to prevent litter from seeds and fruits, but the high ratio of male trees causes high pollen counts. Alterations in exposure to
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
s is another plausible explanation, at present, for the increase in atopic allergy. Endotoxin exposure reduces release of inflammatory
cytokine Cytokines are a broad and loose category of small protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and ...

cytokine
s such as TNF-α, IFNγ,
interleukin-10 Interleukin 10 (IL-10), also known as human cytokine synthesis inhibitory factor (CSIF), is an anti-inflammation, inflammatory cytokine. In humans, interleukin 10 is encoded by the ''IL10'' gene. IL-10 signals through a receptor complex consisting o ...
, and interleukin-12 from white blood cells (leukocytes) that circulate in the blood. Certain microbe-sensing proteins, known as Toll-like receptors, found on the surface of cells in the body are also thought to be involved in these processes. Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine Water chlorination, chlorination and purification of drinking water supplies. Recent research has shown that some common parasites, such as Parasitic worm, intestinal worms (e.g., hookworms), secrete chemicals into the gut wall (and, hence, the bloodstream) that immunosuppressant, suppress the immune system and prevent the body from attacking the parasite. This gives rise to a new slant on the hygiene hypothesis theory—that co-evolution of humans and parasites has led to an immune system that functions correctly only in the presence of the parasites. Without them, the immune system becomes unbalanced and oversensitive. In particular, research suggests that allergies may coincide with the delayed establishment of gut flora in infants. However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms. Clinical trials have been initiated to test the effectiveness of certain worms in treating some allergies. It may be that the term 'parasite' could turn out to be inappropriate, and in fact a hitherto unsuspected Mutualism (biology), symbiosis is at work. For more information on this topic, see Helminthic therapy.


Pathophysiology


Acute response

In the early stages of allergy, a type I hypersensitivity reaction against an allergen encountered for the first time and presented by a professional antigen-presenting cell causes a response in a type of immune cell called a T helper cell, TH2 lymphocyte; a subset of T cells that produce a
cytokine Cytokines are a broad and loose category of small protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and ...

cytokine
called interleukin-4 (IL-4). These TH2 cells interact with other lymphocytes called B cells, whose role is production of antibodies. Coupled with signals provided by IL-4, this interaction stimulates the B cell to begin production of a large amount of a particular type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor (a kind of Fc receptor called FcεRI) on the surface of other kinds of immune cells called
mast cell#REDIRECT Mast cell A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem ...

mast cell
s and
basophil Basophils are a type of white blood cell. Basophils are the least common type of granulocyte, representing about 0.5% to 1% of circulating white blood cells. However, they are the largest type of granulocyte. They are responsible for inflammato ...

basophil
s, which are both involved in the acute inflammatory response. The IgE-coated cells, at this stage, are sensitized to the allergen. If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils. Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complex interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called degranulation, during which they release
histamine Histamine is an organic nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele a ...

histamine
and other inflammatory chemical mediators (
cytokine Cytokines are a broad and loose category of small protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and ...

cytokine
s, interleukins, leukotrienes, and prostaglandins) from their granule (cell biology), granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucus, mucous secretion, nerve stimulation, and smooth muscle contraction. This results in rhinorrhea, itchiness, dyspnea, and
anaphylaxis Anaphylaxis is a serious allergic reaction Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reac ...
. Depending on the individual, allergen, and mode of introduction, the symptoms can be system-wide (classical anaphylaxis), or localized to particular body systems; asthma is localized to the respiratory system and eczema is localized to the dermis.


Late-phase response

After the chemical mediators of the acute response subside, late-phase responses can often occur. This is due to the migration of other leukocytes such as neutrophils, lymphocytes, eosinophils and macrophages to the initial site. The reaction is usually seen 2–24 hours after the original reaction. Cytokines from mast cells may play a role in the persistence of long-term effects. Late-phase responses seen in
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
are slightly different from those seen in other allergic responses, although they are still caused by release of mediators from eosinophils and are still dependent on activity of TH2 cells.


Allergic contact dermatitis

Although allergic contact dermatitis is termed an "allergic" reaction (which usually refers to type I hypersensitivity), its pathophysiology actually involves a reaction that more correctly corresponds to a type IV hypersensitivity reaction. In type IV hypersensitivity, there is activation of certain types of T cells (CD8+) that destroy target cells on contact, as well as activated macrophages that produce hydrolytic enzyme, hydrolytic
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates in ...

enzyme
s.


Diagnosis

Effective management of allergic diseases relies on the ability to make an accurate diagnosis. Allergy testing can help confirm or rule out allergies.NICE Diagnosis and assessment of food allergy in children and young people in primary care and community settings, 2011 Correct diagnosis, counseling, and avoidance advice based on valid allergy test results reduces the incidence of symptoms and need for medications, and improves quality of life. To assess the presence of allergen-specific IgE antibodies, two different methods can be used: a skin prick test, or an allergy blood test. Both methods are recommended, and they have similar diagnostic value. Skin prick tests and blood tests are equally cost-effective, and health economic evidence shows that both tests were cost-effective compared with no test. Also, early and more accurate diagnoses save cost due to reduced consultations, referrals to secondary care, misdiagnosis, and emergency admissions. Allergy undergoes dynamic changes over time. Regular allergy testing of relevant allergens provides information on if and how patient management can be changed, in order to improve health and quality of life. Annual testing is often the practice for determining whether allergy to milk, egg, soy, and wheat have been outgrown, and the testing interval is extended to 2–3 years for allergy to peanut, tree nuts, fish, and crustacean shellfish. Results of follow-up testing can guide decision-making regarding whether and when it is safe to introduce or re-introduce allergenic food into the diet.


Skin prick testing

Skin testing is also known as "puncture testing" and "prick testing" due to the series of tiny punctures or pricks made into the patient's skin. Small amounts of suspected allergens and/or their extracts (''e.g.'', pollen, grass, mite proteins, peanut extract) are introduced to sites on the skin marked with pen or dye (the ink/dye should be carefully selected, lest it cause an allergic response itself). A small plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected "intradermally" into the patient's skin, with a needle and syringe. Common areas for testing include the inside forearm and the back. If the patient is allergic to the substance, then a visible inflammatory reaction will usually occur within 30 minutes. This response will range from slight reddening of the skin to a full-blown Urticaria, hive (called "wheal and flare") in more sensitive patients similar to a mosquito bite. Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with +/− meaning borderline reactivity, and 4+ being a large reaction. Increasingly, allergists are measuring and recording the diameter of the wheal and flare reaction. Interpretation by well-trained allergists is often guided by relevant literature. Some patients may believe they have determined their own allergic sensitivity from observation, but a skin test has been shown to be much better than patient observation to detect allergy. If a serious life-threatening anaphylactic reaction has brought a patient in for evaluation, some allergists will prefer an initial blood test prior to performing the skin prick test. Skin tests may not be an option if the patient has widespread skin disease, or has taken antihistamines in the last several days.


Patch testing

Patch testing is a method used to determine if a specific substance causes allergic inflammation of the skin. It tests for delayed reactions. It is used to help ascertain the cause of skin contact allergy, or
contact dermatitis Contact dermatitis is a type of inflammation of the skin. Some symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, and swelling. The rash isn't contagious or life-threatening, but it can be very uncomfortabl ...

contact dermatitis
. Adhesive patches, usually treated with a number of common allergic chemicals or skin sensitizers, are applied to the back. The skin is then examined for possible local reactions at least twice, usually at 48 hours after application of the patch, and again two or three days later.


Blood testing

An allergy blood test is quick and simple, and can be ordered by a licensed health care provider (''e.g.'', an allergy specialist) or general practitioner. Unlike skin-prick testing, a blood test can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. Adults and children of any age can get an allergy blood test. For babies and very young children, a single needle stick for allergy blood testing is often more gentle than several skin pricks. An allergy blood test is available through most Medical laboratory, laboratories. A sample of the patient's blood is sent to a laboratory for analysis, and the results are sent back a few days later. Multiple allergens can be detected with a single blood sample. Allergy blood tests are very safe, since the person is not exposed to any allergens during the testing procedure. The test measures the concentration of specific IgE, IgE antibodies in the blood. Quantitative analysis (chemistry), Quantitative IgE test results increase the possibility of ranking how different substances may affect symptoms. A rule of thumb is that the higher the IgE antibody value, the greater the likelihood of symptoms. Allergens found at low levels that today do not result in symptoms can not help predict future symptom development. The quantitative allergy blood result can help determine what a patient is allergic to, help predict and follow the disease development, estimate the risk of a severe reaction, and explain cross-reactivity. A low total IgE level is not adequate to rule out
sensitization Sensitization is a non-associative learning process in which repeated administration of a stimulus results in the progressive amplification of a response. Sensitization often is characterized by an enhancement of response to a whole class of sti ...
to commonly inhaled allergens. statistics, Statistical methods, such as ROC curves, predictive value calculations, and likelihood ratios have been used to examine the relationship of various testing methods to each other. These methods have shown that patients with a high total IgE have a high probability of allergic sensitization, but further investigation with allergy tests for specific IgE antibodies for a carefully chosen of allergens is often warranted. Laboratory methods to measure specific IgE antibodies for allergy testing include enzyme-linked immunosorbent assay (ELISA, or EIA), radioallergosorbent test (RAST) and fluorescent enzyme immunoassay (FEIA).


Other testing

Challenge testing: Challenge testing is when small amounts of a suspected allergen are introduced to the body orally, through inhalation, or via other routes. Except for testing food and medication allergies, challenges are rarely performed. When this type of testing is chosen, it must be closely supervised by an allergist. Elimination/challenge tests: This testing method is used most often with foods or medicines. A patient with a suspected allergen is instructed to modify his diet to totally avoid that allergen for a set time. If the patient experiences significant improvement, he may then be "challenged" by reintroducing the allergen, to see if symptoms are reproduced. Unreliable tests: There are other types of allergy testing methods that are unreliable, including applied kinesiology (allergy testing through muscle relaxation), cytotoxicity testing, urine autoinjection, skin titration (Rinkel method), and provocative and neutralization (subcutaneous) testing or sublingual provocation.


Differential diagnosis

Before a diagnosis of allergic disease can be confirmed, other possible causes of the presenting symptoms should be considered. Vasomotor rhinitis, for example, is one of many illnesses that share symptoms with allergic rhinitis, underscoring the need for professional differential diagnosis. Once a diagnosis of
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
, rhinitis,
anaphylaxis Anaphylaxis is a serious allergic reaction Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reac ...
, or other allergic disease has been made, there are several methods for discovering the causative agent of that allergy.


Prevention

Giving peanut products early may decrease the risk allergies while only breastfeeding during at least the first few months of life may decrease the risk of dermatitis. There is no good evidence that a mother's diet during pregnancy or breastfeeding affects the risk. Nor is there evidence that delayed introduction of certain foods is useful. Early exposure to potential allergens may actually be protective. Fish oil supplementation during pregnancy is associated with a lower risk. Probiotic supplements during pregnancy or infancy may help to prevent
atopic dermatitis Atopic dermatitis (AD), also known as atopic eczema, is a long-term type of inflammation of the skin (dermatitis Dermatitis (also known as eczema) is inflammation of the skin Skin is the layer of usually soft, flexible outer tissue coveri ...

atopic dermatitis
.


Management

Management of allergies typically involves avoiding what triggers the allergy and medications to improve the symptoms.
Allergen immunotherapy Allergen immunotherapy, also known as desensitization or hypo-sensitization, is a medical treatment for environmental allergies Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity Hypersensitivi ...
may be useful for some types of allergies.


Medication

Several medications may be used to block the action of allergic mediators, or to prevent activation of cells and degranulation processes. These include antihistamines, glucocorticoids, epinephrine (medication), epinephrine (adrenaline), mast cell stabilizers, and antileukotriene agents are common treatments of allergic diseases. Anticholinergic, Anti-cholinergics, decongestants, and other compounds thought to impair eosinophil chemotaxis, are also commonly used. Although rare, the severity of
anaphylaxis Anaphylaxis is a serious allergic reaction Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reac ...
often requires epinephrine (medication), epinephrine injection, and where medical care is unavailable, a device known as an epinephrine autoinjector may be used.


Immunotherapy

Allergen
immunotherapy Immunotherapy or biological therapy is the treatment of disease by activating or suppressing the immune system. Immunotherapies designed to elicit or amplify an immune response are classified as activation immunotherapies, while immunotherapies ...
is useful for environmental allergies, allergies to insect bites, and asthma. Its benefit for food allergies is unclear and thus not recommended. Immunotherapy involves exposing people to larger and larger amounts of allergen in an effort to change the immune system's response. Meta-analyses have found that injections of allergens under the skin is effective in the treatment in allergic rhinitis in children and in asthma. The benefits may last for years after treatment is stopped. It is generally safe and effective for allergic rhinitis and Allergic conjunctivitis, conjunctivitis, allergic forms of asthma, and stinging insects. The evidence also supports the use of sublingual immunotherapy for rhinitis and asthma but it is less strong. For seasonal allergies the benefit is small. In this form the allergen is given under the tongue and people often prefer it to injections. Immunotherapy is not recommended as a stand-alone treatment for asthma.


Alternative medicine

An experimental treatment, enzyme potentiated desensitization (EPD), has been tried for decades but is not generally accepted as effective. EPD uses dilutions of allergen and an enzyme, beta-glucuronidase, to which T-lymphocytes, regulatory, T-regulatory lymphocytes are supposed to respond by favoring desensitization, or down-regulation, rather than sensitization. EPD has also been tried for the treatment of autoimmune diseases but evidence does not show effectiveness. A review found no effectiveness of homeopathic treatments and no difference compared with placebo. The authors concluded that, based on rigorous clinical trials of all types of homeopathy for childhood and adolescence ailments, there is no convincing evidence that supports the use of homeopathic treatments. According to the National Center for Complementary and Integrative Health, U.S, the evidence is relatively strong that saline nasal irrigation and butterbur are effective, when compared to other alternative medicine treatments, for which the scientific evidence is weak, negative, or nonexistent, such as honey, acupuncture, omega 3's, probiotics, astragalus, capsaicin, grape seed extract, Pycnogenol, quercetin, spirulina, stinging nettle, tinospora or guduchi.


Epidemiology

The allergic diseases—hay fever and asthma—have increased in the Western world over the past 2–3 decades. Increases in allergic asthma and other atopic disorders in industrialized nations, it is estimated, began in the 1960s and 1970s, with further increases occurring during the 1980s and 1990s, although some suggest that a steady rise in sensitization has been occurring since the 1920s. The number of new cases per year of atopy in developing countries has, in general, remained much lower.


Changing frequency

Although genetic factors govern susceptibility to atopic disease, increases in atopy have occurred within too short a time frame to be explained by a genetic change in the population, thus pointing to environmental or lifestyle changes. Several hypotheses have been identified to explain this increased rate; increased exposure to perennial allergens due to housing changes and increasing time spent indoors, and changes in cleanliness or hygiene that have resulted in the decreased activation of a common immune control mechanism, coupled with dietary changes, obesity and decline in physical exercise. The hygiene hypothesis maintains that high living standards and hygienic conditions exposes children to fewer infections. It is thought that reduced bacterial and viral infections early in life direct the maturing immune system away from T helper cell, TH1 type responses, leading to unrestrained TH2 responses that allow for an increase in allergy. Changes in rates and types of infection alone however, have been unable to explain the observed increase in allergic disease, and recent evidence has focused attention on the importance of the Gut flora, gastrointestinal microbial environment. Evidence has shown that exposure to food and fecal-oral route, fecal-oral pathogens, such as hepatitis A, ''Toxoplasma gondii'', and ''Helicobacter pylori'' (which also tend to be more prevalent in developing countries), can reduce the overall risk of atopy by more than 60%, and an increased rate of parasitic infections has been associated with a decreased prevalence of asthma. It is speculated that these infections exert their effect by critically altering TH1/TH2 regulation. Important elements of newer hygiene hypotheses also include exposure to endotoxins, exposure to pets and growing up on a farm.


History

Some symptoms attributable to allergic diseases are mentioned in ancient sources. Particularly, three members of the Roman Julio-Claudian dynasty (Augustus, Claudius and Britannicus) are suspected to have a family history of atopy. The concept of "allergy" was originally introduced in 1906 by the Vienna, Austria, Viennese pediatrician Clemens von Pirquet, after he noticed that patients who had received injections of horse serum or smallpox vaccine usually had quicker, more severe reactions to second injections. Pirquet called this phenomenon "allergy" from the Ancient Greek language, Ancient Greek words wikt:ἄλλος, ἄλλος ''allos'' meaning "other" and wikt:ἔργον, ἔργον ''ergon'' meaning "work". All forms of hypersensitivity used to be classified as allergies, and all were thought to be caused by an improper activation of the immune system. Later, it became clear that several different disease mechanisms were implicated, with the common link to a disordered activation of the immune system. In 1963, a new classification scheme was designed by Philip George Houthem Gell, Philip Gell and Robin Coombs that described four types of hypersensitivities, hypersensitivity reactions, known as Type I to Type IV hypersensitivity. With this new classification, the word ''allergy'', sometimes clarified as a true allergy, was restricted to type I hypersensitivities (also called immediate hypersensitivity), which are characterized as rapidly developing reactions involving IgE antibodies. A major breakthrough in understanding the mechanisms of allergy was the discovery of the antibody class labeled
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(IgE). IgE was simultaneously discovered in 1966–67 by two independent groups: Kimishige Ishizaka, Ishizaka's team at the Children's Asthma Research Institute and Hospital in Denver, Colorado, and by Gunnar Johansson and Hans Bennich in Uppsala, Sweden. Their joint paper was published in April 1969.


Diagnosis

Radiometric assays include the radioallergosorbent test (RAST test) method, which uses IgE-binding (anti-IgE) antibodies labeled with radioactive isotopes for quantifying the levels of IgE antibody in the blood. Other newer methods use colorimetric or fluorescence-labeled technology in the place of radioactive isotopes. The RAST methodology was invented and marketed in 1974 by Pharmacia Diagnostics AB, Uppsala, Sweden, and the acronym RAST is actually a brand name. In 1989, Pharmacia Diagnostics AB replaced it with a superior test named the ImmunoCAP Specific IgE blood test, which uses the newer fluorescence-labeled technology. American College of Allergy, Asthma and Immunology, American College of Allergy Asthma and Immunology (ACAAI) and the American Academy of Allergy, Asthma, and Immunology, American Academy of Allergy Asthma and Immunology (AAAAI) issued the Joint Task Force Report "Pearls and pitfalls of allergy diagnostic testing" in 2008, and is firm in its statement that the term RAST is now obsolete: The new version, the ImmunoCAP Specific IgE blood test, is the only specific IgE assay to receive Food and Drug Administration approval to quantitatively report to its detection limit of 0.1kU/l.


Medical specialty

An allergist is a physician specially trained to manage and treat allergies,
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asthma
and the other allergic diseases. In the United States physicians holding certification by the American Board of Allergy and Immunology (ABAI) have successfully completed an accredited educational program and evaluation process, including a proctored examination to demonstrate knowledge, skills, and experience in patient care in allergy and immunology. Becoming an allergist/immunologist requires completion of at least nine years of training. After completing medical school and graduating with a medical degree, a physician will undergo three years of training in internal medicine (to become an internist) or pediatrics (to become a pediatrician). Once physicians have finished training in one of these specialties, they must pass the exam of either the American Board of Pediatrics (ABP), the American Osteopathic Board of Pediatrics (AOBP), the American Board of Internal Medicine (ABIM), or the American Osteopathic Board of Internal Medicine (AOBIM). Internists or pediatricians wishing to focus on the sub-specialty of allergy-immunology then complete at least an additional two years of study, called a fellowship, in an allergy/immunology training program. Allergist/immunologists listed as ABAI-certified have successfully passed the certifying examination of the ABAI following their fellowship. In the United Kingdom, allergy is a subspecialty of general medicine or pediatrics. After obtaining postgraduate exams (Membership of the Royal College of Physicians, MRCP or Membership of the Royal College of Paediatrics and Child Health, MRCPCH), a doctor works for several years as a specialist registrar before qualifying for the General Medical Council specialist register. Allergy services may also be delivered by immunologists. A 2003 Royal College of Physicians report presented a case for improvement of what were felt to be inadequate allergy services in the UK. In 2006, the House of Lords convened a subcommittee. It concluded likewise in 2007 that allergy services were insufficient to deal with what the Lords referred to as an "allergy epidemic" and its social cost; it made several recommendations.


Research

Low-allergen foods are being developed, as are improvements in skin prick test predictions; evaluation of the atopy patch test; in wasp sting outcomes predictions and a rapidly disintegrating epinephrine tablet, and anti-Interleukin 5, IL-5 for eosinophilic diseases. Aerobiology is the study of the biological particles passively dispersed through the air. One aim is the prevention of allergies due to pollen.Galán, C., Smith, M., Thibaudon, M., Frenguelli, G., Oteros, J., Gehrig, R., ... & EAS QC Working Group. (2014). Pollen monitoring: minimum requirements and reproducibility of analysis. Aerobiologia, 30(4), 385–395.


See also

* List of allergens * Allergic shiner * Histamine intolerance * Oral allergy syndrome


References


External links

* * {{Authority control Allergology, Effects of external causes Immunology Respiratory diseases Immune system Immune system disorders Wikipedia medicine articles ready to translate RTTEM