If you think pizza and chocolate are the bad guys behind breakouts, think again. These days, acne is blamed mostly on heredity and hormones. During puberty, a surge in male hormones called androgens (women have them, too) stimulates an increase of sebum, responsible for keeping skin moist, and keratin, needed to make hair. When too much of either clogs a hair follicle, acne can result.
Eating a cheesy pizza probably won't make much difference to your skin, but what will make a difference—a positive one—is eating more fruits, vegetables and other foods that help keep hormones in balance and fight inflammation.