How does acne develop?

The sebaceous glands produce oil (also called sebum) which normally travels via hair follicles to the skin surface. However, dried oil, dead skin cells, and bacteria can cover the hair follicles, blocking the oil coming from the sebaceous glands. When follicles become plugged, skin bacteria (called Propionibacterium acnes, or P. acnes) begin to grow inside the follicles, causing inflammation. Acne progresses in the following manner:

1. Incomplete blockage of the hair follicle results in blackheads (a semisolid, black plug in a pore).
2. Complete blockage of the hair follicle results in whiteheads (a semisolid, white plug in a pore).
3. Infection and irritation cause abscesses (areas of pus) to form.

Eventually, the plugged follicle bursts, spilling oil, skin cells, and the bacteria onto the skin surface. In turn, the skin becomes irritated and pimples or lesions begin to develop. The basic acne lesion is called a comedo or comedone.

Acne can be superficial (pimples without abscesses) or deep (when the inflamed pimples push down into the skin, causing pus-filled cysts that rupture and result in larger abscesses).