During adolescence, there is a sudden spurt in the secretion of sex hormones that cause increased formation of oils (sebum) from the sebaceous glands of the skin.

Sebaceous glands are secretary glands that open into hair follicles and skin pores. There is accumulation of oily secretions from the sebaceous glands due to blockage of the external pores in the skin. Consequently, the oils and dead skin cells are trapped, and form small "plugs" known as "comedones" within the hair follicles of the skin. Bacteria act on these plugs aggravating the infection and causes the inflammation of the skin eruptions.

The plug causes the hair follicle to bulge causing white-heads and if the top of the plug is darkened, it becomes black-heads. If the plug causes the wall of the follicle to rupture, the oil, dead skin cells, and bacteria found normally on the surface of the skin can enter the skin and form small infected areas called pustules also known as pimples or "zits".

Family history of acne can also contribute to the development of acne.

Other hormonal changes, can occur with menstrual periods, pregnancy, use of birth control pills, or stress and can aggravate acne.