According to Porter, it's typically caused by the increase in the male hormone called androgen. Androgen overstimulates oil glands and alters the behavior of skin cells, contributing to acne flare-ups.
If you think hormonal acne is just something women have to deal with, you'd be surprised to find out that this isn't the case at all. It actually affects both men and women. Porter explained that men are more likely to develop severe forms of acne (including inflammatory and cystic) during adolescence. Luckily for them, these skin problems tend to diminish once they are adults.
Unfortunately, ladies have the reverse issue. While women tend to have milder breakouts when they're younger, they are more prone to develop adult acne. This can be explained by the fact that women's hormones fluctuate more.