Comedones Acne

Comedones are the skin-coloured, small bumps (papules) frequently found on the forehead and chin of those with acne. A single lesion is a comedo.

Open comedones are blackheads; black because of surface pigment (melanin), rather than dirt
Closed comedones are whiteheads; the follicle is completely blocked
Microcomedones are so small that they are not visible to the naked eye
Macrocomedones are facial closed comedones that are larger than 2–3 mm in diameter
A giant comedo is a type of cyst in which there is a clear blackhead-like opening in the skin
Solar comedones are found on the cheeks and chin of older people, and are thought to be due to sun damage

What causes comedones?

Comedones arise when cells lining the sebaceous duct proliferate (cornification), and there is increased sebum production. A comedo is formed by the debris blocking the sebaceous duct and hair follicle. It is now known that comedones also involve inflammation (see causes of acne).

The development of comedones may involve the following factors:

Excessive activity of the male sex hormone 5-testosterone (DHT) within skin cells
Reduced linoleate (the salt of the essential fatty acid, linoleic acid) in sebum causing more scale and reduced barrier function
Proinflammatory cytokines (cell signalling proteins), such as Interleukin 1 (IL-1) and IL-8, produced by cells lining the follicle in response to activation of the innate immune system
Free fatty acids made from sebum by acne bacteria
Overhydrated skin premenstrually, from moisturisers or in humid conditions
Contact with certain chemicals including oily pomades, isopropyl myristate, propylene glycol and some dyes in cosmetics
Rupture of the follicle by injury such as squeezing pimples, abrasive washing, chemical peels or laser treatments
Smoking – comedonal acne is more common in smokers than in non-smokers
Certain dietary factors may contribute to comedonal acne, particularly milk products and high glycaemic-index foods (sugars and fats)