What is acne?

Acne is a chronic inflammatory disease of the sebaceous hair follicles. Each follicle contains a tiny hair and multiple sebaceous glands.

Under normal circumstances, sebum, the oily substance made by the sebaceous glands, travels up the hair follicle and out to the skin's surface. Acne vulgaris is caused by an excessive amount of oil production by the skin, blockage of the openings to the oil producing glands (resulting in tiny blackheads) and also due to a bacterium, Propionibacterium acnes (P. acnes) which causes inflammation in the blocked glands. These three factors seem to work together in order to produce the red and yellow spots so characteristic of acne.

Occasionally these spots can develop into large cysts (so called nodular or cystic acne) which often results in scarring.


Although a bacterium is involved, acne cannot be caught from other people.

Acne develops on those areas of the skin where sebaceous glands are most numerous: the face, scalp, neck, chest, back, and upper arms and shoulders.

Acne is sometimes confused with Rosacea, which is a rash which looks like acne but on a red background. It is a skin disease that tends to be more common in the over 40s.