Scientists think a hormone called androgen plays a role in acne. Among other things, androgen stimulates the sebum-producing glands. After puberty, boys produce 10 times as much androgen as girls, and so it's not surprising that more boys than girls develop severe cases of acne. Also, bacteria called Corynebacterium acnes, which cause skin fats to break down into irritating chemicals, can directly contribute to an outbreak. Some oily cosmetics and shampoos can, on rare occasions, trigger acne in people who are prone to get it.
Many young women notice that they get more pimples around the time of their menstrual periods.
In fact, some studies have shown that up to 70 percent of women notice their acne worsening the week before their periods. But there's no scientific evidence to back up these claims. Still, if you notice that outbreaks increase after you eat certain foods, it makes sense to eat as little of them as possible. Oily skin and hair don't actually cause acne, experts say. Although there is an association between the severity of acne and the amount of oil a person's skin produces, not all people with oily skin have acne.