• Researchers investigated how sun-seeking behavior by people on vacation affects the skin microbiome.
• They found that sun-seeking behavior leads to short-term changes in skin bacterial diversity, which can lead to conditions such as eczema.
• Further studies are needed to understand what this means for long-term skin health.

Human skin hosts many bacteria, fungi, and viruses, which play a key role in maintaining skin homeostasis.

It is well-established that high doses of ultraviolet radiation (UVR) damage DNA in skin cells and induce inflammation and photoaging.

However, research is comparably limited on how UVR affects skin bacteria in vivo.

While some studies suggest that UVR may positively affect the skin by decreasing levels of opportunistic pathogens among other factors, other research reports that UVR-induced microbiota imbalances can lead to chronic inflammation and conditions such as eczema and psoriasis.

How ultraviolet radiation can affect the skin

Researchers recently examined the effects of short-term holiday-related sun exposure on skin.

They report that sun exposure affects the diversity and composition of skin microbiota, but that changes reverse after 28 days of returning home.

The study was published in the journal Frontiers in Aging.

“This study suggests that increased sun exposure, or at least tanning, during a sunny holiday is associated with short-term shifts in the skin microbiome,” said Dr. Adela Rambi G. Cardones, MHSc, a professor and chief of the Division of Dermatology at The University of Kansas Health System who was not involved in the study.

“Further studies need to be done to determine what the underlying cause of this shift was and what the ultimate health implications are,” she told Medical News Today.

Details on the skin and sun exposure study

For the study, the researchers recruited 21 North European residents, comprised of four men and 17 women, with an average age of about 33 years.

The researchers collected skin swabs from the participants prior to them going on holiday to a sunny destination for a minimum of seven days.

They also collected swabs immediately after the vacation as well as 28 days and 84 days later.

The participants were split into three groups according to their skin color one day after returning from holiday. The groups included:

• ‘Seekers’: Those who picked up a tan while on holiday
• ‘Tanners’: Those who already had a tan prior to departure and maintained it while abroad
• ‘Avoiders’: Those who did not tan while abroad and maintained the same skin tone before and after

After conducting a genetic analysis of the skin samples, the researchers found that three bacteria made up 94% of all skin microbiota samples at all time points before and after the holiday. They included actinobacteria, proteobacteria, and firmicutes.

Immediately after the participants returned from vacation, the researchers reported that seekers and tanners had significantly lower levels of proteobacteria than the avoider group. By days 28 and 84 however, levels of proteobacteria had returned to pre-holiday levels.

Meanwhile, levels of actinobacteria and firmicutes remained consistent across the groups over all time points.

“This implies that the presumed effects of sun exposure on the skin microbiome are not long-lasting,” said Rambi.

When asked how sun exposure may have affected the skin’s microbiome in this way, Dr. Adelaide Hebert, a professor of dermatology with McGovern Medical School at UTHealth Houston who was not involved in the study, told Medical News Today:

“The skin may be altered by sun exposure in terms of the normal gram negative bacteria that live on the skin surface. These bacteria keep the other normal bacteria ‘in check’.”

Eczema and skin microbiome

Previous research indicates that decreased levels of proteobacteria are linked to skin conditions such as eczema.

Medical News Today spoke on this topic with Dr. J. Wes Ulm, a bioinformatic scientific resource analyst, and biomedical data specialist at the National Institutes of Health who was not involved in the study.

Ulm noted that the skin’s microbiome is composed of microbial species just like the gut and that as disruptions such as antibiotic usage or dietary changes can affect the gut microbiome, stresses like UVR can also disrupt the skin microbiome.

“There’s a delicate interplay of interactions that determines how the skin’s immune system reacts to its environment. When it’s altered, an inflammatory response can ensue. This appears to be the case with shifts in skin microbiota, which can provoke the local immune system to produce inflammation linked to eczema and dermatitis,” he said.

Rambi added that while studies show that decreased levels of proteobacteria relative to other bacteria may be linked to conditions such as eczema, further studies are needed to know whether it is a causative link.

Limitations of the study

Hebert noted that the findings may be limited as the study included few participants and few men.

“Additionally, the study did not take into account if the subjects were swimming, hiking, or had done other various activities,” she added.

Ulm indicated that the study only included British vacationers, so the findings may not apply to other demographics. He further noted that the study didn’t account for modulating factors such as sunscreen usage or vacationing in other locations.

“These are all fairly customary limitations for an early study, and provide a roadmap for further investigations to add further context and pinpoint the underlying factors,” he said.

Considering future research directions, Ulm said that it would be interesting to see how sunscreens of varying SPF levels and types impact the results, whether similar findings would surface in different demographics, and how vacationing in different parts of the world with varying levels of ozone protection affects results.

Implications of the study on sun exposure

“The good news is that the skin’s microbiome reconstitutes itself in fairly short order once individuals are out of the sun for a while. Thus limited, short-term exposures don’t appear to markedly increase the risk of eczema or dermatitis in a sustained manner,” said Ulm.

He noted, however, that it remains unclear whether and how repeated sun exposure may affect the skin over months or years.

He noted that while short-term exposure may not cause too many problems for autoimmune or inflammatory conditions such as eczema or psoriasis, repeated exposure may be more problematic.

“Population-level studies conducted over several years may be of interest here. In general, it’s already known that excessive sun exposure, especially without protective garments or sunscreen, are harmful in many ways, and this adds yet another factor for vacationers to weigh,” he concluded.

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