Acne is a common skin condition where the pores of your skin become blocked by hair, sebum (an oily substance), bacteria and dead skin cells. Those blockages produce blackheads, whiteheads, nodules and other types of pimples. Acne is the most common skin condition that people experience; it's estimated that 80% of people between the ages of 11 to 30 will have at least a mild form of acne at some point in their lives.