Don't go swimming while wearing sunscreen - unless you want cancer.
A compound used in the protective lotions1 turns toxic2 when it reacts with chlorine and ultraviolet rays, researchers found.
Avobenzone is considered the most popular sun-blocker in the world due to its ability to absorb sunlight at different wave lengths - preventing skin damage.
But Russian scientists suggest the UV-filtering compound forms cancer-causing toxins3 when exposed to a mixture of sun and chlorinated water.
Aldehydes, phenols and chlorinated acetyl benzenes were created in experiments simulating swimmers wearing sunscreen.
The latter two are considered extremely toxic and are strongly linked to deadly tumours4 and infertility5, Lomonosov Moscow State University experts say.
While a study earlier this year hinted that aldehydes can raise the risk of cancer as they interfere6 with the body's natural repair mechanism.