Sebaceous follicle with comedone

Evolution of Acne

• Acne occurs in the so-called "sebaceous follicles" that exist in most adults on the face, chest and back, the usual sites for the development of acne vulgaris.
• These are distinguished from usual hair follicles by having very large sebaceous glands and very small hairs.
• The first stage in the development of a lesion is the formation of a "micro-comedone".  This is a mass of abnormal follicular epithelium, lipid, and bacteria. The follicle is distended.
• Subsequently, there are two directions for evolution.

  The first is predominance of the lipid and epithelial component which leads to either "blackhead" or "whitehead" comedones.

  The second possibility is the predominance of the inflammatory component, thought to be derived largely from the bacterial population resident in the follicle and, in this case, the follicle wall ruptures, exposing the contents to the body’s inflammation and immune system. Various components of inflammation may be important but, in the worst cases, a significant foreign body reaction results in nodules and cysts that leave significant scarring.

• Androgens, whatever their effect, appear to be a significant requirement in almost all cases for the development of acne vulgaris. Conversely, the presence of acne in patients otherwise not predisposed (e.g. the very young) should lead to the suspicion that abnormal androgen concentrations are present.