Baby acne is usually seen on the cheeks, chin, and forehead. It can be present at birth but usually develops around 3 to 4 weeks of age. Baby acne occurs when hormonal changes in the body stimulate oil glands in the baby's skin. The condition can look worse when the baby is crying or fussy, or any other instance that increases blood flow to the skin. Baby acne is harmless and usually resolves on its own within several weeks.

Each pore on the surface of the skin is an opening to a canal called a follicle. The follicle also contains a hair and an oil gland (sebaceous gland). The oil gland helps remove old skin cells, keeps the skin lubricated, and prevents drying of tissues.

Acne lesions frequently contain pus. This close-up photograph shows small acne pustules with surrounding inflammation (erythema).

Blackheads, or open comedones, are common in acne. Clogged hair follicles reflect light irregularly to produce this black hue.

Blackheads, or open comedones, are common in acne. Clogged hair follicles reflect light irregularly to produce this black hue.

Cystic acne may occur across the upper chest as well as on the back.

The face is the most common location of acne. Here, there are 4 to 6 millimeter red (erythematous) pustules, some with bridging scars and fistulous tract formation (connecting passages). Severe acne may have a profound psychological impact and may cause scarring. Effective treatments are available for this type of acne.

Acne frequently occurs on the back. Here, there are 2 to 6 millimeter wide erythematous (red) pustules with large open and closed comedones. Permanent scarring may follow a severe case of acne. Men are more often affected on their shoulders and back than are women.

Cystic acne, or nodulocystic acne, is the most severe form of acne. Both pustules and hard red bumps are present in the skin. This form of acne is more difficult to treat and often requires taking an oral vitamin A derivative.

Cystic acne, or nodulocystic acne, is the most severe form of acne. Both pustules and red bumps are present in the skin and scarring can be seen. The back is a common site for acne.

Acne affects the areas of the skin that contain sebaceous glands, including the face, upper chest, and back. Acne occurs most commonly during adolescence. Many new treatment regimens are available for acne, especially for the most severe types.

Acne may persist into adulthood.