A comedo is a clogged

hair follicle The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between h ...

(pore) in the skin.

Keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

(skin debris) combines with oil to block the follicle. A comedo can be open (blackhead) or closed by skin (whitehead) and occur with or without

acne Acne, also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, black ...

. The word "comedo" comes from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''comedere'', meaning "to eat up", and was historically used to describe parasitic worms; in modern medical terminology, it is used to suggest the worm-like appearance of the expressed material. The chronic inflammatory condition that usually includes comedones, inflamed papules, and pustules (

pimples A pimple is a kind of comedo that results from excess Sebaceous gland#Sebum, sebum and dead skin cells getting trapped in the pores of the skin. In its aggravated state, it may evolve into a Cutaneous condition, pustule or papules. Pimples can ...

) is called acne. Infection causes inflammation and the development of

pus Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during bacterial or fungal infection. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collection ...

. Whether a skin condition classifies as acne depends on the number of comedones and infection. Comedones should not be confused with

sebaceous filament A sebaceous filament is a tiny collection of sebum and dead skin cells around a hair follicle, which usually takes the form of a small, yellow to off-white hair-like strand when expressed from the skin. These filaments are naturally occurring, an ...

s. Comedo-type ductal carcinoma ''in situ'' (DCIS) is not related to the skin conditions discussed here. DCIS is a noninvasive form of breast cancer, but comedo-type DCIS may be more aggressive, so may be more likely to become invasive.

Causes

Oil production in the

sebaceous glands A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...

increases during puberty, causing comedones and

to be common in adolescents. Acne is also found premenstrually and in women with

polycystic ovarian syndrome Polycystic ovary syndrome, or PCOS, is the most common endocrine disorder in women of reproductive age. The syndrome is named after the characteristic cysts which may form on the ovaries, though it is important to note that this is a sign and no ...

. Smoking may worsen acne.

Oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

rather than poor hygiene or dirt causes blackheads to be black. Washing or scrubbing the skin too much could make it worse, by irritating the skin. Touching and picking at comedones might cause irritation and spread infection. What effect shaving has on the development of comedones or acne is unclear. Some skin products might increase comedones by blocking pores, and greasy hair products (such as

pomades Pomade (; French ''pommade'') or pomatum is a greasy, waxy, or water-based substance that is used to style hair. Pomade generally gives the user's hair a shiny and slick appearance. It lasts longer than most hair-care products, and often re ...

) can worsen acne. Skin products that claim to not clog pores may be labeled

noncomedogenic The term acne cosmetica refers to acne caused by or aggravated by cosmetics. The mechanism is thought to be chemically induced plugging of the pilosebaceous orifice. This became a significant problem for dermatologists in the 1970s and 1980s, bu ...

or nonacnegenic. Make-up and skin products that are oil-free and water-based may be less likely to cause acne. Whether dietary factors or sun exposure make comedones better, worse, or neither is unknown. A hair that does not emerge normally, an

ingrown hair Ingrown hair is a condition where a hair curls back or grows sideways into the skin. The condition is most prevalent among people who have coarse or curly hair. It may or may not be accompanied by an infection of the hair follicle (folliculitis) o ...

, can also block the pore and cause a bulge or lead to infection (causing inflammation and

). Genes may play a role in the chances of developing acne. Comedones may be more common in some ethnic groups. People of

Latino Latino or Latinos most often refers to: * Latino (demonym), a term used in the United States for people with cultural ties to Latin America * Hispanic and Latino Americans in the United States * The people or cultures of Latin America; ** Latin A ...

and recent African descent may experience more inflammation in comedones, more comedonal acne, and earlier onset of inflammation.

Pathophysiology

Comedones are associated with the

pilosebaceous unit A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...

, which includes a

and

sebaceous gland A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...

. These units are mostly on the face, neck, upper chest, shoulders, and back. Excess keratin combined with

sebum A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest nu ...

can plug the opening of the follicle. This small plug is called a microcomedo.

Androgens An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...

increase sebum (oil) production. If sebum continues to build up behind the plug, it can enlarge and form a visible comedo. A comedo may be open to the air ("blackhead") or closed by skin ("whitehead"). Being open to the air causes oxidation, which turns it black. ''

Cutibacterium acnes ''Cutibacterium acnes'' (formerly ''Propionibacterium acnes'') is the relatively slow-growing, typically aerotolerant Anaerobic organism, anaerobic, gram-positive bacterium (rod) linked to the skin condition of acne vulgaris, acne; it can also ca ...

'' is the suspected infectious agent in acne. It can proliferate in sebum and cause inflamed

pustules A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this sy ...

(pimples) characteristic of acne. Nodules are inflamed, painful, deep bumps under the skin. Comedones that are 1 mm or larger are called macrocomedones. They are closed comedones and are more frequent on the face than neck. Solar comedones (sometimes called senile comedones) are related to many years of exposure to the sun, usually on the cheeks, not to acne-related pathophysiology.

Management

Using nonoily cleansers and mild soap may not cause as much irritation to the skin as regular soap. Blackheads can be removed across an area with commercially available pore-cleansing strips (which can still damage the skin by leaving the pores wide open and ripping excess skin) or the more aggressive

cyanoacrylate Cyanoacrylates are a family of strong fast-acting adhesives with industrial, medical, and household uses. They are derived from ethyl cyanoacrylate and related esters. The cyanoacrylate group in the monomer rapidly polymerizes in the presence ...

method used by dermatologists. Squeezing blackheads and whiteheads can remove them, but can also damage the skin. Doing so increases the risk of causing or transmitting infection and scarring, as well as potentially pushing any infection deeper into the skin. Comedo extractors are used with careful hygiene in beauty salons and by dermatologists, usually after using steam or warm water.

Complementary medicine Alternative medicine is any practice that aims to achieve the healing effects of medicine despite lacking biological plausibility, testability, repeatability, or evidence from clinical trials. Complementary medicine (CM), complementary and alt ...

options for acne in general have not been shown to be effective in trials. These include aloe vera,

pyridoxine Pyridoxine, is a form of vitamin B6 found commonly in food and used as a dietary supplement. As a supplement it is used to treat and prevent pyridoxine deficiency, sideroblastic anaemia, pyridoxine-dependent epilepsy, certain metabolic disorde ...

(vitamin B₆), fruit-derived acids,

kampo , often known simply as , is the study of traditional Chinese medicine in Japan following its introduction, beginning in the 7th century. It was adapted and modified to suit Japanese culture and traditions. Traditional Japanese medicine use ...

(Japanese herbal medicine),

ayurvedic Ayurveda () is an alternative medicine system with historical roots in the Indian subcontinent. The theory and practice of Ayurveda is pseudoscientific. Ayurveda is heavily practiced in India and Nepal, where around 80% of the population rep ...

herbal treatments, and acupuncture. Some acne treatments target infection specifically, but some treatments are aimed at the formation of comedones, as well. Others remove the dead layers of the skin and may help clear blocked pores.

Dermatologists Dermatology is the branch of medicine dealing with the skin.''Random House Webster's Unabridged Dictionary.'' Random House, Inc. 2001. Page 537. . It is a speciality with both medical and surgical aspects. A dermatologist is a specialist medical ...

can often extract open comedones with minimal skin trauma, but closed comedones are more difficult. Laser treatment for acne might reduce comedones, but dermabrasion and laser therapy have also been known to cause scarring. Macrocomedones (1 mm or larger) can be removed by a dermatologist using surgical instruments or cauterized with a device that uses light. The acne drug

isotretinoin Isotretinoin, also known as 13-''cis''-retinoic acid and sold under the brand name Accutane among others, is a medication primarily used to treat severe acne. It is also used to prevent certain skin cancers (squamous-cell carcinoma), and in th ...

can cause severe flare-ups of macrocomedones, so dermatologists recommend removal before starting the drug and during treatment. Some research suggests that the common acne medications

retinoid The retinoids are a class of chemical compounds that are vitamers of vitamin A or are chemically related to it. Retinoids have found use in medicine where they regulate epithelial cell growth. Retinoids have many important functions throughout t ...

s and

azelaic acid Azelaic acid (AzA) is an organic compound with the formula HOOC(CH2)7 COOH. This saturated dicarboxylic acid exists as a white powder. It is found in wheat, rye, and barley. It is a precursor to diverse industrial products including polymers an ...

are beneficial and do not cause increased pigmentation of the skin. If using a retinoid, sunscreen is recommended.

Rare conditions

Favre–Racouchot syndrome occurs in sun-damaged skin and includes open and closed comedones. ''

Nevus comedonicus '' Nevus comedonicus'' (also known as a comedo nevus) is characterized by closely arranged, grouped, often linear, slightly elevated papules that have at their center keratinous plugs resembling comedones.James, William; Berger, Timothy; Elston, Dir ...

'' or comedo nevus is a benign

hamartoma A hamartoma is a mostly benign, local malformation of cells that resembles a neoplasm of local tissue but is usually due to an overgrowth of multiple aberrant cells, with a basis in a systemic genetic condition, rather than a growth descended fr ...

(birthmark) of the

around the oil-producing gland in the skin. It has widened open hair follicles with dark keratin plugs that resemble comedones, but they are not actually comedones. Dowling–Degos disease is a genetic pigment disorder that includes comedo-like

lesions A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...

and scars. Familial dyskeratotic comedones are a rare autosomal-dominant genetic condition, with keratotic (tough) papules and comedo-like lesions.

References

External links

*
What causes blackheads, Treatment and Prevention
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