Pores are tiny openings in the skin that release sweat and oil, but some people experience clogged pores more often than others. Clogged pores occur when oil can’t flow freely, often due to “the overproduction of oil trapped by dead cells,” says dermatologist Geeta Yadav, MD. Dirt, makeup, and pore-clogging (comedogenic) ingredients can also contribute to blockages.

Comedogenic ingredients don’t directly cause acne but “make it much more likely that pimples will form,” explains dermatologist Rachel Nazarian, MD. For those with oily skin or acne-causing bacteria, these ingredients can worsen breakouts.

The exact cause of pore-clogging isn’t fully understood, but “ingredients can interact poorly with sebum or be too thick for it to pass through,” says Yadav. These ingredients are often occlusive, forming a seal that traps oil, especially in oily skin types.

To reduce breakouts, it’s important to avoid certain ingredients. Here’s a list of seven pore-clogging ingredients dermatologists recommend steering clear of if you’re acne-prone.