Acne is a very common skin disorder of the pilosebaceous units (PSUs). PSUs consist of sebaceous glands that connect to hair follicles (canals) lined with keratinocytes. The sebaceous glands produce sebum (skin oil). Acne is often inflammatory and is characterized by comedones (clogged pores) and pimples (papules and pustules), due in part to the excessive production of sebum. Acne is not a serious medical condition, and can usually be kept under control with treatment. Although scarring is common, treatment during and after an outbreak can help.

When excessive amounts of sebum and dead keratinocytes accumulate in the hair follicle, they often solidify as a soft plug. The plug may be complete and form a whitehead (closed comedone) or may be incomplete and form a blackhead (open comedone). These plugged, sebum–filled follicles allow overgrowth of Propionibacterium acnes (P. acnes), which are skin bacteria that are normally present in hair follicles. P. acnes break the sebum down into substances that irritate the skin and cause inflammation. This inflammation may lead to pimples, cysts or nodules.

Although acne is not a serious medical condition, it often causes great emotional distress. It may have a significant impact on social relationships, self-esteem or a person’s outlook on life. Many acne sufferers demonstrate social withdrawal, poor body image and feelings of depression, anger and frustration. Acne sufferers may also experience a higher rate of unemployment. Acne myths, such as the belief that acne is linked to poor hygiene, may contribute to this poor social regard.

Acne is the most common skin condition affecting people worldwide. According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), nearly 85 percent of all people between the ages of 12 and 24 develop acne and nearly 17 million people in the United States have acne.

Acne can affect people of all ages, but is most common in teenagers. It usually occurs in puberty (typically between the ages of 10 and 13), when androgens (male sex hormones) increase in both males and females. This increase in androgens causes the sebaceous glands to become bigger and more active. Onset may occur in adulthood or breakouts that began during adolescence may continue into adulthood. Most cases of acne last between five to 10 years.

Typically, the severity of acne decreases by the age of 30, but this is not always the case. It is not uncommon for people in their 20s or 30s to have the condition, and it may continue to affect people in their 40s and 50s. During adolescence, acne is more common in males than in females. In adulthood, it affects women more often than men.