They say leave nothing but footprints at the beach, but a new study reveals we're also leaving our microbiome behind, which can make us prone to infection.
According to the research, taking a dip in the sea washes away millions of protective bacteria, fungi and viruses that were once happily chilling on our skin.
The study's lead author claims that after taking a swim, "normal resident bacteria are washed off, while ocean bacteria are deposited onto the skin."
So if you like swimming in the sea every now and then, should you be concerned?
Find out more in the video above.