Common acne (or "acne vulgaris") is almost a rite of passage among many Western youths going through puberty. Although the cause is unknown, it is important not to confuse this condition with other forms of acne that have known causes that can be quite easily treated: summer and "tropical" acne, caused by a hot, humid climate; cystic acne, which can be treated with isotretinoin, a Vitamin A derivative; etc.

Common acne, which usually appears on the face, neck, and shoulders, is accompanied by papules (or pimples) or lesions (called "comedos") with either black centers (pustules) or nodules created by overgrowth of connective tissue. Some lesions are deep-seated and can cause scaring.

Predisposing factors known to influence acne include hereditary tendencies and disturbances in the androgen-estrogen balance. External factors can include exposure to halogens, vitamin deficiencies, exposure to certain chemicals such as tar and chlorinated hydrocarbons, etc. Acne normally begins at puberty, when the body increases secretion of androgen in both males and females, thereby increasing the size and activity of the pilosebaceous glands. In females the lesions may worsen just before menstruation. Bacteria are known to worsen existing acne, which explains the benefit some sufferers receive from antibiotic therapy.