Gisela Telis / ScienceNOW

If you were plagued by pimples in your teen years, you may have had bacteria to blame — but not all of them. Researchers have found that not all strains of the bacteria commonly associated with acne are created equal: Some may cause problem skin, but one appears to protect the skin and keep it healthy. The discovery may help dermatologists develop new, strain-specific treatments for acne.

Although acne is practically a rite of passage — more than 80 percent of Americans suffer from the skin condition, which can cause pimples, cysts and red, inflamed skin, at some point in their lives — it’s not entirely understood. Past studies have pointed to Propionibacterium acnes, a bacterium that lives in the skin’s follicles and pores, as a potential culprit, but that work had not precisely revealed its role.

Molecular biologist Huiying Li of UCLA’s David Geffen School of Medicine and colleagues decided to take a closer look at the microbe.

The researchers found a number of different strains of the microbe, including 66 that had never been identified before. When they sequenced the genomes of each strain, they discovered that two of the strains, RT4 and RT5, were found predominantly in people with acne and that one strain, RT6, was found almost exclusively in people with clear skin.