As if bleeding for a week isn't fun enough, acne before or during a woman's period is very common.
It's all about the hormones -- in this case, ones that are thought of as male hormones. Women produce androgens, too, however, and just before menstruation, they trigger the body to produce extra oil.
Oil is good for your skin, but too much can clog your pores and cause pimples. Sometimes birth control can stop androgen from making excess oil, which means fewer breakouts [source: American Academy of Dermatology]. It's been so successful in doing so that the FDA has approved certain brands of birth control to treat acne [source: Mayo Clinic].