Causes of acne before your period
The average menstrual cycle lasts about 28 days, and hormones fluctuate continuously throughout the cycle. During the first half of the menstrual cycle, the levels of estrogen rise. During the second half of the cycle, the levels of progesterone rise. As your period approaches, the levels of both of these hormones fall. Meanwhile, your levels of testosterone stay about the same. This means that before and during your period, your testosterone activity is relatively higher than that of estrogen and progesterone.
These hormonal shifts can cause all sorts of skin changes. The rise in progesterone during the middle of the luteal phase stimulates the sebaceous glands to secrete sebum. Sebum is an oily, thick substance that naturally lubricates the skin. The hormonal interactions in the luteal phase may also cause skin to swell, compressing the pores. This can cause sebum to build up under the surface of the skin.
Additionally, having higher testosterone levels before and during your period can stimulate the sebaceous glands even more, causing them to secrete more sebum. The effects of this increased sebum are different for different people. For some people, it can produce a healthy glow. For others, it can cause premenstrual acne as the pores become clogged along with dirt, debris, and dead skin cells.
Increased sebum creates a perfect breeding ground for a bacteria that causes acne, called Cutibacterium acnes. Your immune system reacts to these bacteria, causing inflammation and pimples before your period.