Acne is a common skin condition characterized by the occurrence of comedones (blackheads and whiteheads), pimples, and sometimes cysts or nodules. Causes of Acne - Overproduction of sebum - Clogged pores - Bacterial growth - Hormonal fluctuations - Genetics - Stress Types of Acne - Comedonal Acne: Blackheads and whiteheads - Inflammatory Acne: Red, painful pimples - Cystic Acne: Large, painful cysts - Adult-Onset Acne: Acne that occurs in adults