So what exactly makes an ingredient likely to clog your pores? Long answer short: We don’t really know for sure. “Comedogenicity isn’t entirely understood,” Yadav says. “In some cases, ingredients can interact poorly with your sebum, making it thicker, while other ingredients are too thick for sebum to pass through.” To that point, pore-clogging ingredients are typically occlusive, adds board-certified dermatologist Melanie Palm, MD. They sit on top of the skin, forming a seal that ends up trapping oil, particularly when someone has oily skin to start. Palm also points out that some pore-clogging ingredients add more oils to the skin, causing cells to stick together and adhere more tightly instead of sloughing off as they typically should from the lining of the pore.

Now that you understand why comedogenic ingredients can increase your breakouts, it’s time to learn which ones specifically to consider avoiding. Ahead, read all about seven pore-clogging ingredients dermatologists say are worth steering clear of if you’re prone to acne.