Comedones open

Acne Severity Predominant Lesions Closed Comedones Open Comedones Papules Pustules Nodules Scarring... 

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. ... 

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. 

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. 

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