Teenage acne is thought to be triggered by increased levels of a hormone called testosterone, which occurs during puberty. The hormone plays an important role in stimulating the growth and development of the penis and testicles in boys, and maintaining muscle and bone strength in girls. The sebaceous glands are particularly sensitive to hormones. It’s thought that increased levels of testosterone cause the glands to produce much more sebum than the skin needs. It’s thought that many cases of adult acne are caused by the changes in hormone levels that many women have at certain times. These times include: periods – some women have a flare-up of acne just before their period; pregnancy – many women have symptoms of acne at this time, usually during the first 3 months of their pregnancy and polycystic ovary syndrome – a common condition that can cause acne, weight gain and the formation of small cysts inside the ovary.