Acne is among the most common skin conditions in the world, and 85% of people will experience acne during their lifetime. In spite of the high prevalence of acne, however, researchers and dermatologists are still largely unsure of why pimples form in the first place.

New research published in the Journal of Investigative Dermatology, however, may help acne experts better understand what happens on a cellular level when we break out.

Plenty of research into acne and acne treatment has been done over the past 10-15 years. Until now, it’s been attributed to a variety of factors: sebaceous glands overproducing oil and sebum, abnormal skin growth around hair follicles, bacterial colonization around hair and sebaceous glands, and inflammation.

Inflammation has been an especially hot topic in acne research. Many treatment regimens differentiate between what works for non-inflammatory acne like whiteheads and blackheads and inflammatory acne like red or pus-filled pimples. But recent research has shown that some form of inflammation occurs with all acne, even if it’s not visible on the surface of the skin.

Researchers discovered this after investigating the immune response to acne, and they found that immune cells formed around hair follicles before swelling and inflammation was visible on the surface. The immune system reacts when bacteria is detected, resulting in swelling that can be negated by current treatments that also inhibit the immune system.

Surprisingly, the oil gland is part of that immune system, according to the recent paper published in the Journal of Investigative Dermatology. The bacteria that causes acne feeds on sebum produced by oil glands, but the cells that compose oil glands also function as components of the immune system. When oil glands create inflammation, it’s a sign that they’re trying to keep bacteria out, but some glands tend to overreact, causing even more acne.

This is some of the first research to shed light on the function of sebaceous gland cells as part of the immune system, not just oil producers. Researchers hope to use the data to further understand the body’s immune response to acne bacteria so they can find better ways to treat pimples and breakouts.