Research shows ocean water can change your skin microbiome, but experts say it’s still safe for most people to dive in.

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Experts say you probably don’t have to shower after swimming in the ocean, but it’s still not a bad idea. Getty Images

Your skin microbiome is altered after you swim in the ocean, according to research presented at a conference on microbiology.

However, experts interviewed by Healthline say there really isn’t any reason to avoid the beach this summer.

At the annual meeting this weekend for the American Society for Microbiology, scientists shared research that showed exposure to ocean water through swimming changes the composition and diversity of a person’s skin microbiome.

“Participants swam in relatively clean water, and still their microbiomes were significantly different after swimming than they were before. Organisms present in the water were still detected on the skin 24 hours after swimming. This would indicate that if pathogens are present in the water, they may also be present on the swimmer’s skin even 24 hours after they swim,” Marisa Chattman Nielsen, MS, a PhD student at the University of California, Irvine, and lead author of the study, told Healthline.

Previous studies have found associations between swimming in the ocean and infections, due in part to poor water quality at beaches from wastewater or stormwater runoff. Other studies have also found that changes in the microbiome may make a person more vulnerable to infection.

In undertaking their study, the researchers from UC Irvine enlisted nine volunteers who hadn’t used sunscreen, had infrequent exposure to the sea, hadn’t bathed in the past 12 hours, and hadn’t taken antibiotics in the previous six months.

The participants were swabbed on the back of their calf before entering the water and swabbed again after they swam for 10 minutes and dried off completely. They were then swabbed six hours and 24 hours after their swim.

Before they entered the water, the participants had different communities of bacteria on their skin. But after their swim, the microbiome communities of all the participants were similar. They had also completely changed from the microbiota present before their swim.

At six hours, their microbiomes began to return to what they were before swimming.

“Ocean water is a unique exposure, because not only does it wash off normal skin bacteria, it also deposits foreign bacteria onto the skin. This is very different than a shower or even a pool, because those water sources usually have a low concentration of bacteria,” Chattman Nielsen said.

Her team’s research hasn’t been published yet in a peer-reviewed journal.

Although ocean water may change the skin microbiome, this doesn’t necessarily mean a person is at risk.

Dr. Dana Hawkinson, an assistant professor at the University of Kansas School of Medicine, says in most cases swimming in the ocean wouldn’t put a person at risk for infection.

“Humans have been swimming in the ocean since the dawn of time. In general, other than becoming a meal for a shark or other marine life, swimming is pretty safe. Factors that may increase risk of infection would be immunosuppression or having an open wound where the ocean organism may come into contact with your body and subsequently cause infection,” Hawkinson told Healthline.

According to the Centers for Disease Control and Prevention, ocean water can be contaminated with animal waste, sewage spills, stormwater runoff, fecal matter, and germs from the rectal areas of swimmers.

Such contamination can cause infection in the gastrointestinal system, the skin, ears, eyes, and respiratory system, as well as to wounds. The most common symptom of infection from recreational swimming is diarrhea.

Stephen Morse, PhD, a professor of epidemiology at Columbia University in New York, says swimmers shouldn’t fear the ocean this summer. Just take sensible precautions when necessary.

“Don’t swim where you see ‘red tides’ (algal blooms) or fish die-offs. The authorities will almost always close these places to recreational use anyway. Immunocompromised people and weak swimmers should be especially careful. If you think you caught a disease or injured yourself while swimming, see a doctor,” Morse said.

But Chattman Nielsen says the research shouldn’t alarm swimmers.

“This research isn’t meant to scare anyone. We already know that people can get infections from their environment, and the ocean is no different. Much of the bacteria found in the ocean does not cause human disease. Enjoy your time at the beach, and don’t forget to take a quick shower when you’re done,” she said.

One pathogen that’s made headlines recently is the bacteria species called Vibrio vulnificus.

A recent report, published in the journal Annals of Internal Medicine, found that Vibrio vulnificus may be spreading to beaches not previously affected by the bacteria.

The infection is typically found in warm waters like those in the Gulf of Mexico, but the report suggests the bacteria has moved farther north.

“This bug can be in the water, and if you go into the water and you have open sores or cuts on your body, it can aggressively enter those lesions and give you necrotizing fasciitis, a kind of flesh-eating bacteria, which can be associated with bloodstream infections,” William Schaffner, MD, a professor of medicine in the division of infectious diseases at Vanderbilt University Medical School in Nashville, told Healthline.

“There have been reports now of several Vibrio vulnificus infections in people on the eastern coast of the U.S. off New Jersey shores,” he said.

But experts say the odds of contracting such an infection or other illnesses from the sea are slim.

“For people who know how to swim and are competent swimmers, the benefits of ocean swimming greatly outweigh the small potential risks. Ocean swimming is great exercise, relaxing, and puts a person in touch with nature. It’s good for the soul. People should continue to enjoy the oceans and protect them,” Dr. Jeffrey Klausner, MPH, a professor of medicine in the division of infectious diseases at UCLA, told Healthline.

And Schaffner isn’t worried about picking up an infection from the ocean, either. He plans to visit Florida soon and intends to swim at the beach.