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a plug of keratin and sebum within the dilated orifice of a hair follicle. The dark color is caused not by dirt but by the discoloring effect of air on the sebum in the clogged pore. Infection may cause it to develop into a pustule or boil. See also acne vulgaris. Called also open comedo.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


1. A skin lesion consisting of a hair follicle that is occluded with sebum and keratin, appearing black at the surface.
2. An infectious disease of turkeys and some wildfowl that is caused by a protozoan (Histomonas meleagridis) and results in lesions of the intestine and liver. Also called enterohepatitis, histomoniasis, infectious enterohepatitis.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A blocked sebaceous gland which is open to air, where the secretions oxidise, turning black.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


Open comedo A blocked sebaceous gland which is open to air, where the secretions oxidize, turning black. Cf Whitehead.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


A disease chiefly affecting turkeys, caused by Histomonas meleagridis and characterized by ulcerative and necrotic lesions of the liver and cecum, acute onset, and a high mortality rate. It is transmitted inside the eggs of the nematode Heterakis gallinae, which is primarily responsible for maintaining and spreading the infection.
Synonym(s): blackhead (2) .

o·pen com·e·do

(ō'pĕn kom'ĕ-dō)
A comedo with a wide opening on the skin surface capped with a melanin-containing blackened mass of epithelial debris.
Synonym(s): blackhead (1) .
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


An accumulation of fatty sebaceous material in a sebaceous gland or hair follicle, with oxidation of the outer layer, causing a colour change from white to dark brown or black. Blackheads, or comedones, occur in the skin disorder ACNE.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


A plug of fatty cells capped with a blackened mass.
Mentioned in: Rosacea
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

Patient discussion about blackhead

Q. I have this blackhead on my cheek area for about a year..,How do I remove it?

A. This type of blackhead you are describing sounds like comedonal (non-inflammatory) acne, as opposed to acne that is inflammatory or severe inflammatory (which usually will not remain for a year on the skin). There are many basic local treatments which can be found at pharmacies over-the-counter. Whether it is gel or cream (which are rubbed into the pores over the affected region), bar soaps or washes - it is important to keep the skin clean of bacteria, that may worsen blackheads.

More discussions about blackhead
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References in periodicals archive ?
Comedones represent pilosebaceous ductal hyperkeratinization that begins at the junction of the isthmus and the infundibulum [1, 2].
The resulting skin lesions can be either comedones or inflammatory in nature.
Both agents significantly reduced the number of inflammatory lesions and comedones (SOR: B).
Isotretinoin also reduces cell shedding and the stickiness of cells in the follicles, which helps prevent the development of comedones.
Non-inflamed lesions or comedones, inflamed lesions, and/or scars characterize acne occurring on the face, chest, shoulders, or upper arms.
Clinical Features (4): Acne vulgaris is characterized by comedones, papules, pustules, and nodules in a sebaceous distribution (e.g., face, upper chest, back).
Acne vulgaris is a chronic inflammatory disease of pilosebaceous units characterized by comedones, papules and pustules and less frequently by nodules, cysts and scars.1
Acne severity index (ASI) score was estimated by such formula: 0.25x comedone number + 1 x papule number + 2 x pustule number= ASI score.
Acne vulgaris is a common dermatological disorder of the pilosebaceous unit presenting usually at puberty.1 It is characterized by the formation of open and closed comedones (non-inflammatory lesions), papules, pustules, and nodulocystic lesions (inflammatory lesions) generally affecting the face, arms, and back.
Condition Form of lesion Distribution of lesions Acne * Follicular; pustular * Widespread across the Vulgaris comedones whole face, chest, back, neck and shoulders Rosacea * Greater vascular * Central part of the involvement face (across the cheeks * Erythema and nose) Telangiectasis * Hyperplasia of the nose leading to rhinophyma Perioral * Eczematous appearance * Primarily located around Dermatitis (small dry, inflamed the mouth and eyes lesions) Environmental Medicine
In a large retrospective case series, various skin abnormalities such as follicular papules, comedones, hypertrophic pilosebaceous units, angiokeratoma of Fordyce, leucoderma macules, and haemangiomas have been shown to be associated with NLCS.
Acne vulgaris is a chronic inflammatory disease of pilosebaceous units characterized by comedones, papules, pustules, nodules, cysts, abscesses, and later on sometimes as widespread scarring.