Pores: We’ve all got these tiny openings in our skin for releasing sweat and oil, but for some people, they can be more temperamental than others. Or, rather, clogged pores happen more often to some of us than others.

Clogged pores happen when oil doesn’t or can’t flow through them as it should, explains board-certified dermatologist Geeta Yadav, MD. “Typically, this is caused by the overproduction of oil that then becomes trapped by dead cells that haven’t properly shed from the lining of the pore.

Makeup, dirt, and/or comedogenic ingredients can also block the pore, and prevent that flow of oil through it,” she says.

Comedogenic is essentially a word for pore-clogging, and while these types of ingredients aren’t the sole cause of acne and breakouts—there are several factors—they certainly won’t help the situation. “Pore-clogging ingredients make it much more likely that pimples will form,” says board-certified dermatologist Rachel Nazarian, MD.

“In someone who has naturally oily skin or who harbors the bacteria that causes acne, using these ingredients is like adding gas to the fire. It’s a dangerous combination that can exacerbate acne and cause consistent breakouts.”

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.