Acne, also known as acne vulgaris, is a long-term skin disease that occurs when hair follicles are clogged with dead skin cells and oil from the skin. It is characterized by blackheads or whiteheads, pimples, oily skin, and possible scarring. It primarily affects areas of the skin with a relatively high number of oil glands, including the face, upper part of the chest, and back. The resulting appearance can lead to anxiety, reduced self-esteem and, in extreme cases, depression or thoughts of suicide.Genetics is thought to be the primary cause of acne in 80% of cases. The role of diet and cigarette smoking is unclear, and neither cleanliness nor exposure to sunlight appear to play a part. In both sexes, hormones called androgens appear to be part of the underlying mechanism. Another frequent factor is excessive growth of the bacterium Propionibacterium acnes, which is normally present on the skin.Many treatment options for acne are available, including lifestyle changes, medications, and medical procedures. Eating fewer simple carbohydrates such as sugar may help. Treatments applied directly to the affected skin, such as azelaic acid, benzoyl peroxide, and salicylic acid, are commonly used. Antibiotics and retinoids are available in formulations that are applied to the skin and taken by mouth for the treatment of acne. However, resistance to antibiotics may develop as a result of antibiotic therapy. Several types of birth control pills help against acne in women. Isotretinoin pills are usually reserved for severe acne due to greater potential side effects. Early and aggressive treatment of acne is advocated by some in the medical community to decrease the overall long-term impact to individuals.In 2015, acne was estimated to affect 633 million people globally, making it the 8th most common disease worldwide. Acne commonly occurs in adolescence and affects an estimated 80–90% of teenagers in the Western world. Lower rates are reported in some rural societies. Children and adults may also be affected before and after puberty. Although acne becomes less common in adulthood, it persists in nearly half of affected people into their twenties and thirties and a smaller group continue to have difficulties into their forties.