What causes acne in women?

Excess testosterone. All women have male hormone, testosterone, in their bodies. An excess can cause acne. This is oftentreated with estrogen, commonly in oral contraceptives. In the bloodstream are compounds called sex hormone binding globulins. Estrogen increases these elements. When sex hormone binding globulin attaches to testosterone, the testosterone is inactivated, ergo less acne.
Many things. Hormones, genetics, hygiene. See your doctor.

Related Questions

What causes acne & facial hair in women in their 30's? Too many hormones or not enough and what to do about it?

Masculinization. Hair pattern is at times hereditary. There could also be hormonal imbalances from normal tissues or abnormal production. You should see your doctor and voice these concerns so it can be diagnosed and corrected.