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A callus is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, but they may occur anywhere on the skin. Some degree of callus, such as on the bottom of the foot, is normal. Calluses are generally not harmful and help prevent
blister A blister is a small pocket of body fluid (lymph, serum, plasma, blood, or pus) within the upper layers of the skin, usually caused by forceful rubbing (friction), burning, freezing, chemical exposure or infection. Most blisters are filled w ...
s, as well as offering protection. However, excessive formation may sometimes lead to other problems, such as a
skin ulceration An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughing o ...
or infection, or cause the affected person to try to offload the affected painful area, which can place excessive stress on the asymptomatic side. Rubbing that is too frequent or forceful will cause
blister A blister is a small pocket of body fluid (lymph, serum, plasma, blood, or pus) within the upper layers of the skin, usually caused by forceful rubbing (friction), burning, freezing, chemical exposure or infection. Most blisters are filled w ...
s, as opposed to calluses, to form.


Cause

Normally, a callus will form on any part of the skin exposed to excess friction over a long period of time. Activities that are known for causing calluses include (but are not limited to) construction work, many sports,
wood carving Wood carving is a form of woodworking by means of a cutting tool (knife) in one hand or a chisel by two hands or with one hand on a chisel and one hand on a mallet, resulting in a wooden figure or figurine, or in the sculptural ornamentatio ...
, playing
musical instruments A musical instrument is a device created or adapted to make musical sounds. In principle, any object that produces sound can be considered a musical instrument—it is through purpose that the object becomes a musical instrument. A person who pl ...
, use of a chef's knife, rock climbing,
hiking Hiking is a long, vigorous walk, usually on trails or footpaths in the countryside. Walking for pleasure developed in Europe during the eighteenth century.AMATO, JOSEPH A. "Mind over Foot: Romantic Walking and Rambling." In ''On Foot: A Histo ...
, martial arts, weight training,
rowing Rowing is the act of propelling a human-powered watercraft using the sweeping motions of oars to displace water and generate reactional propulsion. Rowing is functionally similar to paddling, but rowing requires oars to be mechanically att ...
,
BMX BMX, an abbreviation for bicycle motocross or bike motocross, is a cycle sport performed on BMX bikes, either in competitive BMX racing or freestyle BMX, or else in general street or off-road recreation. History BMX began during the earl ...
ing,
dancing Dance is a performing art form consisting of sequences of movement, either improvised or purposefully selected. This movement has aesthetic and often symbolic value. Dance can be categorized and described by its choreography, by its repertoire ...
(especially
ballet Ballet () is a type of performance dance that originated during the Italian Renaissance in the fifteenth century and later developed into a concert dance form in France and Russia. It has since become a widespread and highly technical form of ...
),
chopping wood Woodchopping (also spelled wood-chopping or wood chopping), called woodchop for short, is a sport that has been around for hundreds of years in several cultures. In woodchopping competitions, skilled contestants attempt to be the first to cut or s ...
,
monkey bars A jungle gym (called a climbing frame in British English) is a piece of playground equipment made of many pieces of material, such as metal pipes or ropes, on which participants can climb, hang, sit, and—in some configurations—slide. Monkey ...
, pacing and wearing high heels. Although calluses can occur anywhere on the body as a reaction to moderate, constant "grinding" pressure, they are most often found on the
foot The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...
(where the most pressure and friction are applied). On the feet, arguably the source of the most problematic calluses, they typically form on the metatarsal-phalangeal joint area ("balls of the foot"), heels and small toes due to the compression applied by tightly fitting shoes. Biologically, calluses are formed by the accumulation of terminally differentiated
keratinocyte Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referred ...
s in the outermost layer of skin. Though the cells of calluses are dead, they are quite resistant to mechanical and chemical damage due to extensive networks of cross-linked proteins and
hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, t ...
keratin intermediate filaments containing many
disulfide bonds In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...
. It is the natural reaction of the palmar or
plantar Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
skin. Too much friction occurring too fast for the skin to develop a protective callus will cause a
blister A blister is a small pocket of body fluid (lymph, serum, plasma, blood, or pus) within the upper layers of the skin, usually caused by forceful rubbing (friction), burning, freezing, chemical exposure or infection. Most blisters are filled w ...
or abrasion instead. Sometimes a callus occurs where there is no rubbing or pressure. These
hyperkeratoses Hyperkeratosis is thickening of the stratum corneum (the outermost layer of the epidermis, or skin), often associated with the presence of an abnormal quantity of keratin,Kumar, Vinay; Fausto, Nelso; Abbas, Abul (2004) ''Robbins & Cotran Patholog ...
can have a variety of causes. Some toxic materials, such as
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...
, can cause thick palms and soles. Some diseases, such as
syphilis Syphilis () is a sexually transmitted infection caused by the bacterium ''Treponema pallidum'' subspecies ''pallidum''. The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, and ...
, can cause thickening of the palms and soles as well as pinpoint hyperkeratoses. There is a benign condition called ''keratosis palmaris et plantaris'', which produces corns in the creases of the fingers and non-weight bearing spaces of the feet. Some of this may be caused by
actinic keratosis Actinic keratosis (AK), sometimes called solar keratosis or senile keratosis, is a pre-cancerous area of thick, scaly, or crusty skin.Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. . Actinic k ...
, which occurs due to overexposure to sun or with age and hormonal shifts.


Corns

A
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
(or ''clavus'', plural ''clavi'') is a cone-shaped callus that penetrates into the dermis, usually on the feet or hands. Corns may form due to chronic pressure or rubbing at a pressure point (in this skin over a bone), or due to scar tissue from a healing wound creating pressure in a weight-bearing area such as the sole of the foot. If there is constant stimulation of the tissue producing the corns, even after the corn is surgically removed, the skin may continue to grow as a corn. The hard part at the center of the corn resembles a funnel with a broad raised top and a pointed bottom. Because of their shape, corns intensify the pressure at the tip and can cause deep tissue damage and ulceration. The scientific name for a corn is ''heloma'' (plural ''helomata''). A hard corn is called a ''heloma durum'', while a soft corn is called a ''heloma molle''. The location of the soft corns tends to differ from that of hard corns. Hard corns occur on dry, flat surfaces of skin. Soft corns (frequently found between adjacent toes) stay moist, keeping the surrounding skin soft. The corn's center is not soft however, but
indurated Friability ( ), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under duress or contact, especially by rubbing. The opposite of friable is indurate. Substances that are designated hazardous, ...
. The specific diagnostic workup and treatments for corns may differ substantially from other forms of calluses.


Prevention

Corns and calluses are easier to prevent than to treat. When it is undesirable to form a callus, minimizing rubbing and pressure will prevent callus formation. Footwear should be properly fitted, gloves may be worn, and protective pads, rings or skin dressings may be used. People with poor circulation or sensation should check their skin often for signs of rubbing and irritation so they can minimize any damage.


Treatment

Calluses and corns may heal by themselves eventually, once the irritation is consistently avoided. They may also be dissolved with keratolytic agents containing
salicylic acid Salicylic acid is an organic compound with the formula HOC6H4CO2H. A colorless, bitter-tasting solid, it is a precursor to and a metabolite of aspirin (acetylsalicylic acid). It is a plant hormone, and has been listed by the EPA Toxic Substa ...
, sanded down with a pumice stone or
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal si ...
sandpaper or filed down with a
callus shaver A callus shaver (also called a credo knife) is a tool for the medical and cosmetic removal of a callus, mainly on the feet (see also pedicure), or hands. Technically speaking, its function is the abrasive treatment of hyperkeratotic skin lesions. ...
, or pared down by a professional such as a
podiatrist A podiatrist ( ) is a medical professional devoted to the treatment of disorders of the foot, ankle, and related structures of the leg. The term originated in North America but has now become the accepted term in the English-speaking world for ...
.


Diabetes

People with diabetes face special skin challenges. Because diabetes affects the
capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...
, the small blood vessels which feed the skin, thickening of the skin with callus increases the difficulty of supplying nutrients to the skin. Callus formation is seen in high numbers of patients with diabetes, and together with absent foot pulses and formation of
hammer toe A hammer toe or contracted toe is a deformity of the muscles and ligaments of the proximal interphalangeal joint of the second, third, fourth, or fifth toe causing it to be bent, resembling a hammer. In the early stage a flexible hammertoe is ...
, -12% having callus formation -56% having callus present this may be an early sign of individuals at an increased risk for foot ulcers. The stiffness of a callus or corn, coupled with the shear and pressure that caused it, may tear the capillaries or adjoining tissue, causing bleeding within the callus or corn. This can often be result of trying to pick, cut, or shave off the callus by yourself at home. Although the bleeding can be small, sometimes small pools of blood or hematoma are formed. The blood itself is an irritant, a foreign body within the callus that makes the area burn or itch. If the pool of blood is exposed to the outside, infection may follow. Infection may also lead to ulceration. This process can be prevented at several places. Diabetic foot infections are the leading cause of diabetic limb
amputation Amputation is the removal of a limb by trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on indi ...
.


Society and culture

Calluses in the hands are frequently associated with
manual labor Manual labour (in Commonwealth English, manual labor in American English) or manual work is physical work done by humans, in contrast to labour by machines and working animals. It is most literally work done with the hands (the word ''manual'' ...
and
blue-collar worker A blue-collar worker is a working class person who performs manual labor. Blue-collar work may involve skilled or unskilled labor. The type of work may involving manufacturing, warehousing, mining, excavation, electricity generation and powe ...
s. During the
Gads Hill Train Robbery The Gads Hill Train Robbery (also known as the Great Missouri Train Robbery) was a crime committed by the James-Younger Gang in Gads Hill, Missouri. In January 1874, five members of the James-Younger gang robbed a train and stole $12,000 in cash. ...
in 1874, the
James–Younger Gang The James–Younger Gang was a notable 19th-century gang of United States, American outlaws that revolved around Jesse James and his brother Frank James. The gang was based in the state of Missouri, the home of most of the members. Membership f ...
purportedly refrained from robbing men with calloused hands, assuming them to be working class laborers. Such notion is also present in
Māori culture Māori culture () is the customs, cultural practices, and beliefs of the indigenous Māori people of New Zealand. It originated from, and is still part of, Eastern Polynesian culture. Māori culture forms a distinctive part of New Zealand c ...
, where the words ''raupā'' and ''raupo'' refer to hands left cracked and chapped due to manual work, and are used as
simile A simile () is a figure of speech that directly ''compares'' two things. Similes differ from other metaphors by highlighting the similarities between two things using comparison words such as "like", "as", "so", or "than", while other metaphors c ...
s for someone deemed a hard worker. Calluses have also been known to develop on the forehead from the frequent prostrations required in
Muslim prayer (, plural , romanized: or Old Arabic ͡sˤaˈloːh, ( or Old Arabic ͡sˤaˈloːtʰin construct state) ), also known as ( fa, نماز) and also spelled , are prayers performed by Muslims. Facing the , the direction of the Kaaba wit ...
; known as a prayer bump or ''zebiba'', such calluses are considered marks of piety in some Muslim countries, and people have been known to take special steps, such as praying on straw mats, to encourage the callus to develop. Calluses may also form on the fingertips from the repeated pressure and friction of playing stringed instruments. This formation of calluses allows the player to repeatedly depress the strings without causing pain. Because of this, callus formation is viewed as something of a rite of passage for beginner string players.


See also

* Hyperkeratosis *
Callosity A callosity is another name for callus, a piece of skin that has become thickened as a result of repeated contact and friction. Primates All Old World monkeys, gibbons, and some chimpanzees have pads on their rears known as ischial callosities. ...
* Catagmatic


References


Further reading

* ''Taber's Cyclopedic Medical Dictionary'', 15th Edition, CL Thomas, M.D., M.P.H., editor, F.A. Davis Company, Philadelphia, PA, 1985. * ''The Merck Manual of Medical Information, Home Edition'', R Berkow, M.D., et al., editors, Merck Research Laboratories, Whitehouse Station, NJ, 1997.


External links

{{Cutaneous ketatosis, ulcer, atrophy, necrobiosis, and vasculitis Foot diseases Skin conditions resulting from physical factors es:Callo fr:Cal (médecine) ko:티눈 io:Kalo it:Callo pl:Modzel pt:Calo tr:Nasır