Acne vulgaris (or simply acne) is a chronic skin condition characterized by areas of blackheads, whiteheads, pimples, greasy skin, and possibly scarring. The resulting appearance may lead to anxiety, reduced self-esteem, and in extreme cases, depression or thoughts of suicide. Genetics is estimated to be the cause of 80% of cases. The role of diet as a cause is unclear. Neither cleanliness nor sunlight appear to be involved. However, cigarette smoking does increase the risk of developing acne and worsens its severity. Acne mostly affects skin with a greater number of oil glands; including the face, upper part of the chest, and back. During puberty in both sexes, acne is often brought on by an increase in androgens such as testosterone. Many treatment options are available to improve the appearance of acne including lifestyle changes, procedures, and medications. Eating fewer simple carbohydrates like sugar may help. Topical benzoyl peroxide, salicylic acid, and azelaic acid are commonly used treatments. Antibiotics and retinoids are available topically and by mouth to treat acne. Resistance, however, may develop to antibiotics. A number of birth control pills may be useful in women. Oral isotretinoin is usually reserved for severe acne due to greater potential side effects. Early and aggressive treatment is advocated by some to lessen the overall long-term impact to individuals. Acne occurs most commonly during adolescence, affecting an estimated 80–90% of teenagers in the Western world. Lower rates are reported in some rural societies. In 2010, acne was estimated to affect 650 million people globally making it the 8th most common disease worldwide. People may also be affected before and after puberty. Though it becomes less common in adulthood than in adolescence, nearly half of people in their twenties and thirties continue to have acne. About 4% continue to have difficulties into their forties.