Acne is an inflammatory disease of the pilosebaceous follicles, caused by an overproduction of sebum. Sebum builds up in the pores, blocking them and forming comedones, which oxidize and turn into blackheads. Comedones can become inflamed due to bacterial growth on the skin, leading to acne breakouts that may become infected and develop into pustules. This can be very painful and often leaves significant scars on the skin, such as pitted scars or depressions.
Acne breakouts tend to appear in areas with high concentrations of sebaceous glands. They primarily occur on the face, especially around the nose, chin, and forehead (the T-zone), but can also affect the back, chest, and arms. Acne can also become chronic, in which case certain measures can be taken to prevent its spread.