Comedos

Combustion aids Combustion emissions Combustion technology Combustion turbines Comedos... 

The pilosebaceous unit of the skin consists of a hair follicle and the surrounding sebaceous glands. An initial acne lesion called a comedo forms when there is a blockage in the pilosebaceous unit.8... 

Keratinization, the sloughing of epithelial cells in the hair follicle, is also a natural process. In acne, however, hyperkem-tinization occurs and causes increased adhesiveness of the sloughed cells. Accumulation of these cells clogs the hair follicle, blocks the flow of sebum, and forms an acne lesion called an open comedo or blackhead. ... 

Propionibacterium acnes (P. acnes), an anaerobic organism, is also found in the normal flora of the skin. This bacteria proliferates in the mixture of sebum and keratinocytes and can result in an inflammatory response producing a closed comedo or whitehead. More severe acne lesions such as pustules, papules, and nodules can also form with inflammatory acne and result in significant scarring if treated inadequately (Fig. 62-2). 

Open comedo or "blackhead" a plugged follicle of sebum, keratinocytes, and bacteria that protrudes from the surface of the skin and appears black or brown in color. Although dark in color, blackheads do not indicate the presence of dirt, but rather an accumulation of melanin. 

Comedolytic An agent that is able to break up or destroy a comedo. 

Comedo (pi. comedones) Dermatitis Dermatitis herpetiformis Plug of dried sebum in the sebaceous duct blackhead Inflammation of the skin Dermatitis marked by grouped erythematous, papular, vesicular, pustular, or bullous lesions occurring in varied combinations... 

A primary factor in the development of acne is an alteration in the pattern of keratinization within the follicle. Increased production and sloughing of keratinocytes correlate with comedo formation. 

Tretinoin (a retinoid topical vitamin A acid) is a comedolytic agent that increases cell turnover in the follicular wall and decreases cohesiveness of cells, leading to extrusion of comedones and inhibition of new comedo formation. It also decreases the number of cell layers in the stratum corneum from about 14 to about five. 

Isotretinoin (Accutane) alters keratinization in the acroinfundibulum of sebaceous glands and shrinks them, thereby reducing sebum excretion and comedo-genesis. These features underlie its usefulness in acne vulgaris, since sebum secretion is a hallmark of acne-prone skin. Furthermore, the drug has antiinflammatory activity. 

Deep cystic acne is a complex condition that involves an interaction between hormones (testosterone), sebum, and bacteria. It starts at puberty when the increase in androgen levels causes greater activity of the sebaceous glands. This leads to increased growth of epidermal tissue, which blocks the follicle and creates a comedo (cyst) composed of sebum, keratin, and bacteria. Irritation of the follicular wall follows, with rupture of the follicle and then an acute inflammatory reaction. This leads to an abscess and finally healing with scar tissue. 

An open comedo or blackhead is a plug of sebum, keratinocytes, and microorganisms blocking a dilated hair follicle opening, whereas a closed comedone or whitehead is a similar plug blocking a closed hair follicle opening to the surface of the skin. 

Comedo, comedones (pi.)—Plug of sebum and keratinous material in a hair folUcle blackhead. 

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