It’s already known that the “healthy glow” of a tan actually represents damage to skin cells.

But a new study of people on vacation has found that sunbathing also can disrupt the skin’s microbiome, altering the populations of bacteria that live on the skin in ways that could be harmful to health.

The microbiome recovers within a month, but during that time a person will be more vulnerable to skin problems, said senior researcher Abigail Langton. She is a lecturer with the University of Manchester’s Center for Dermatology Research, in England.

“During this 28-day post-holiday period of recovery skin may have reduced health, making it more susceptible to infection or irritation due to the loss of Proteobacteria [a type of bacteria that lives on the skin] and the overall change in skin microbiota balance,” Langton said.

For this study, researchers analyzed the skin of 21 healthy volunteers prior to scheduled vacations in sunny locales. The team noted the makeup of the skin’s microbiota, specifically the three main bacterial communities found there.

The research team then analyzed participants’ skin the day they got back, and at 28 and 84 days post-vacation.

The investigators sorted the vacationers into groups based on sun exposure — eight “seekers” who picked up a tan while away, seven “tanners” who already had a tan before they left, and six “avoiders” who had the same skin tone post-holiday.

All the sun-worshipers experienced significant changes in microbial diversity following their trip.

“In our study, those individuals that avoided developing a tan — ‘sun avoiders’ — were the only ones that maintained a diverse skin microbiota post-holiday,” Langton said.

However, the people who picked up a tan during their vacation had a specific reduction in Proteobacteria. Fluctuations in Proteobacteria have been associated with eczema and psoriasis, the researchers noted.

“The fact that sun behavior influences the skin microbiota so acutely was a surprise,” Langton said. “In our future studies we would like to understand why members of the phyla Proteobacteria are particularly sensitive to ultraviolet radiation and how this change in diversity impacts human skin health in the longer term.”

These findings make sense, given that ultraviolet (UV) radiation is often used to sterilize surfaces like lab benches and keyboards, said Dr. Adam Friedman, chair of dermatology with the George Washington School of Medicine and Health Sciences, in Washington, D.C.

“We know UV radiation is antimicrobial. Unrestricted ultraviolet radiation can potentially kill the microorganisms that use our skin as their home, of which there are about 500-plus species,” said Friedman.

“We are big walking petri dishes,” he continued. “UV radiation-induced damage to the skin changes the petri dish, and these changes occur very quickly.”

It is known that UV radiation alone suppresses the skin’s immune response and can cause skin cancers, Friedman noted.

These UV-driven changes in skin microbiome might help produce infections that people develop after their defenses have been lowered by sun exposure.

“We know those organisms that live on our skin actually play a role in controlling the immune response, they protect us from the environment,” Friedman said. “When the diversity goes down, that shift can be pro-inflammatory. During an infection, that can produce an inappropriate immune response.”

Changes in bacteria might even heighten risk of skin cancer, he added.

“Could that disruption of microbial diversity play a role in carcinogenesis? Maybe. I wouldn’t be surprised,” Friedman said.

But he noted there are a wide variety of other factors associated with sunbathing — salty ocean water, sunscreens, even sun-produced hardening of the skin — that also influence the skin’s microbiome.

It’s not clear from this study what should be done to protect the microbiome, Friedman concluded.

“It doesn’t tell us what should we be doing and what should we be avoiding specifically,” Friedman said. “But I think it opens the door for further exploration.”

Future research might determine that a course of prebiotics or other microbiome-protecting agents might be as essential to skin health as sunscreen when a person is outdoors, Friedman said.

In the meantime, Langton and Friedman recommend that everyone protect themselves against the sun when out and about.

“Practicing sun safety is important for everyone, including wearing broad-spectrum sunscreen and finding some shade whenever possible, but especially in the middle of the day, between 11 a.m. and 3 p.m., when the sun is at its strongest,” Langton said.

The new study was published Aug. 8 in the journal Frontiers in Aging.

More information

The U.S. Food and Drug Administration has more about the risks of tanning.

SOURCES: Abigail Langton, PhD, lecturer, University of Manchester’s Center for Dermatology Research, Manchester, England; Adam Friedman, MD, chair, dermatology, George Washington School of Medicine and Health Sciences, Washington, D.C.; Frontiers in Aging, Aug. 8, 2023