Acne spots are caused by the obstructions of hair follicles by sebum (the oily substance secreted by the sebaceous glands.) When a plug of sebum becomes trapped in a follicle, bacteria multiply and the follicle becomes inflamed.
The cause of the change in sebum secretion at puberty is uncertain but it seems to be linked with increased levels in androgen hormones (male sex hormones). There may also be a genetic factor, since acne can run in families.
Some drugs may bring on or aggravate existing acne (eg. Corticosteroids which increase oil production in the skin).
