Acne is the most common skin disorder, and 85 percent of all Americans will experience it some time in their lifetime. While commonly thought to be an adolescent problem, it can appear at any age, most often on the face, back, and chest. The causes of acne are complex, but usually involve the overproduction of oil, the blockage of follicles that release the oil, and the growth of bacteria in those follicles. This can be triggered by many things, including a change in medications or a change in hormone levels caused by stress or other factors. It’s important to treat acne early to avoid scarring.