What your period does to our bodies (the cramps! The cravings!) is pretty irritating. But what it does to our skin is simply not pretty. “When hormone levels surge before your period, they also stimulate your oil glands to go into overdrive,” says dermatologist Josh Zeichner, M.D. “More oil clogs your pores and feeds acne-causing bacteria.All of this explains the pre-menstrual acne flare that many women experience.” Find out the other annoying ways that Aunt Flo can mess with your skin.

Increased Oil Production
During the last 14 days of your cycle, you have low estrogen and high androgen levels. This is when oil production is at its highest, pores become blocked, and pimple formation is common. “Whatever you do, don’t squeeze those pimples, as the process can cause permanent damage, leaving marks and also promoting bacterial infection,” says Kecia Gaither, M.D., vice chairman and director of maternal fetal medicine in the department of obstetrics and gynecology at Brookdale University Hospital and Medical Center, Brooklyn, NY. To stave off breakouts, it’s best to cleanse with a low-pH, anti-inflammatory cleanser, such as Kiehl’s Ultra Facial Cleanser($10, kiehls.com). It’ll decrease bacterial concentration, strengthen your skin’s moisture barrier, and help retain moisture.

Larger Pores
A surge of progesterone and testosterone—which occurs about a week before your period—can cause pores to become clogged with sebum, making them appear larger. “Using a cleanser or treatment with salicylic acid helps purify clogged pores,” says dermatologist Michael Lin, M.D.

Dry Skin
During our periods, levels of estogren are low, which dehydrates skin, says Gaither. Up the ante on your moisturizing routine to retain all the moisture you can.

Increased Sun Sensitivity
Plastic surgeon Dana Khuthaila, M.D., says the hormones that make your pores become clogged can also increase redness and sun sensitivity. You should never skip SPF, but make sure to be extra vigilant about sun protection right before and during your period.