The reason a woman is placed on birth control to clear up acne is to reduce androgens, male sex hormones like testosterone, in her bloodstream. These androgens trigger an excess production of sebum oil that clogs pores and promotes breakouts. When you take birth control, like Yaz, Yasmin or Estrostep, you’re ingesting estrogen and progestin, a synthetic form of progesterone. These hormones help lower the androgen levels and generally leave you with clear skin after three months.
Not all birth control pills have the same effect, though. Androgenic pills, those containing androgen-based progestin (rather than an anti-androgenic progestin), can actually promote acne. The progestins to look out for in these pills include: norgestrel, norethindrone acetate and levonorgestrel.