If a follicle is blocked, the sebum and dead cells become trapped in the follicle, resulting in acne. It is important to stress that this build-up of dead cells and sebum is not usually due to poor hygiene but due to the fact that these skin cells don't shed in the normal way. Acne tends to accompany the hormonal changes which start in adolescence, which is approximately between the ages of 12 to 17. In girls, acne may precede the onset of menstrual periods by one or two years, as result of normal changes in hormone levels. Sebaceous glands are stimulated by androgens, male hormones which are present in both men and women.
Some people are generally more susceptible to the effects of androgens than others.
This is one reason acne may be more severe in certain individuals. Like pore size, research indicates that susceptibility to hormonal influences is a family trait. For these reasons, acne tends to run in families. But teens aren't the only ones to suffer the effects of hormones. Anything that affects hormone levels can cause acne, including pregnancy, birth control pills, corticosteroid medication such as prednisone, menopause, menstrual periods, and other medical conditions.