Acne is the most common skin condition in the US, but its exact causes are poorly understood. A new study uncovers how a common acne drug alters the balance of bacteria in our skin.

Isotretinoin (brand name Accutane) is commonly used to treat severe acne. But the drug comes with a number of potential side effects, including depression and liver damage. It also causes severe birth defects when women take the drug during pregnancy.

A derivative of vitamin A, isotretinoin reduces the size of the oil, or sebaceous, glands in the skin and the amount of oil that is produced. This is thought to reduce the levels of bacteria present in oily skin regions and tone down inflammation.

Exactly how isotretinoin achieves these effects is not known.

Publishing their findings in the Journal of Investigative Dermatology, researchers from Washington University School of Medicine in St. Louis, MO, reveal how isotretinoin changes the skin microbiome, and they suggest a new approach to the way that acne is treated.

Bacterial populations 'healthier'

Dr. William H. McCoy, the lead study author, explains that "[t]here are greasy areas of the skin that support the growth of certain communities of bacteria, and we know that some of them appear to be associated with acne."

The team wanted to find out if isotretinoin would reduce the number of such bacteria, specifically Cutibacterium acnes, which is also known by its former name Propionibacterium acnes.

The study involved 17 individuals with acne who received isotretinoin treatment. The control group was made up of eight individuals—four with and four without acne—who did not receive any treatment.

The research team collected samples from skin on the face of each participant on 4 occasions over a period of 10 months.

The main findings were that treatment with isotretinoin did indeed reduce the number of C. acnes and that the diversity of bacteria on the surface of the skin was increased.

"The drug appears to make the skin less hospitable to acne-causing bacteria," explains Dr. McCoy.

Using next-generation targeted metagenomics analysis, the team also found that several other types of bacteria increased in number with isotretinoin treatment, which had not been linked to acne improvement in the past.

Microbial 'fertilizer' or 'weed killer'

According to the research team, the findings indicate that isotretinoin changes the growth conditions in the skin in favor of more diverse bacterial populations, rather than directly changing the number of bacteria present.

This effect continued even after the treatment was stopped and oil production returned to normal.

"After the treatment, the microbial communities shift to a mix of populations that appears to be healthier, and that shift persists months after the treatment," explains Makedonka Mitreva, PhD, an associate professor of medicine and the senior author of the study.

Understanding how isotretinoin works is just the first step. The team is now working on a larger study in the hope of improving how acne is treated.

"Our study suggests there could be a way to provide some type of microbial 'fertilizer' or 'weed killer' on the skin to help promote the growth of healthy microbes."

—Dr. William H. McCoy

Who would likely benefit from this? Reducing the potential side effects associated with isotretinoin would certainly be a plus for those who take the drug. For pregnant women with severe acne, it could be a game-changer.

"Women often will go without treatment for acne during their pregnancies because there just aren't good therapies that are totally safe to use during that time," explains Dr. McCoy, adding, "They need other options."