Summer is finally here! You spend your free time enjoying the sun and maybe even going to the beach. But do you know that swimming in the ocean can alter the skin microbiota? And in addition, can increase the infection risk? A team of researchers presented clinical results suggesting some interactions between our skin and the ocean at the annual meeting of the American Society for Microbiology.

This clinical trial was motivated by previous studies showing a correlation between swimming at sea, water quality and the infection risk. Indeed, microbiota changes can cause skin, gastrointestinal, or ENT infections including respiratory or ear infections.

The skin microbiota balance would be disturbed by a swim in the ocean

The skin is the body’s largest organ. It houses on its surface a large number of bacteria, yeasts and fungi forming the cutaneous microbiota. The skin is our first defense line. Firstly, thanks to its physical barrier effect; in a second time, by the presence of microorganisms protecting us from colonization and / or infections caused by opportunistic and pathogenic agents. And it turns out that 10 minutes swimming in the ocean are enough to disrupt this ecosystem balance. (dysbiosis)

It is through the cutaneous microbiota analysis of several volunteers (without sunscreen) that the scientists were able to conclude these results. At the beginning of the procedure, participants appeared to have very different skin microbiota from each other. (Remember that the microbiota is specific to each individual). At the end of the trial, after spending 10 minutes swimming in the ocean, the analysis showed that all cutaneous microbiota tended to look like each other! However, this change is temporary.  Indeed, 6 hours later, skin microbiota began to regain its initial composition.

“While swimming normal resident bacteria were washed off while ocean bacteria were deposited onto the skin” according to Marisa Chattman Nielsen, a researcher at the University of California.

Potentially pathogenic bacteria would be present in the ocean

Another discovery is the presence of Vibrio species in each of the volunteers having swan in the ocean and dried with air. They were always present after 6 hours, and even after 24 hours in one volunteer. Note that genus Vibrio includes the bacterium responsible for cholera, even if the majority of species are not pathogenic. This highlights that potentially pathogenic bacteria could settle on our skin.


CHATTMAN NIELSEN M, JIANG SC. Alterations in the human skin microbiome after ocean water exposure. Marine Pollution Bulletin. 2019, 145:595-603