As if coral didn’t have enough to worry about – global warming, pollution and excess UV radiation now threaten 60 percent of the world’s reef systems – there’s a new menace on the block, and it fits in your pocket: sunscreen.

According to recent studies, some of the UV filtering ingredients in sunscreen have been proven to cause bleaching in the algae that lives on coral, thus killing the entire structure. The same harmful compounds (including 4-methylbenzylidene camphor, or 4-MBC, and octocrylene, or OC) can also get absorbed by fish and may accumulate over time.

Sejal Choksi, program director for environmental watchdog group Baykeeper, told the San Francisco Chronicle “[almost] 80 percent of our water in the U.S. shows trace amounts of chemicals from personal care products, which could be sunscreens, lotions, colognes or medications.”

The UN World Trade Organization estimates that 78 million tourists – swimmers, snorkelers, divers and others – visit coral reefs each year, releasing between 4,000 to 6,000 tons of sunscreen into the water. Several marine reserves in Mexico – Xel-Ha and Xcaret – have banned the use of sunscreens that use oils and chemical ingredients.

The issue puts travelers in a difficult position: slathering on sunscreen wards off skin cancer but contributes to the destruction of critical environmental diversity. Natural sunscreens present a good alternative: the nonprofit Environmental Working Group maintains a list of health and beauty products that use only natural ingredients – no chemical additives. You can find them online at www.cosmeticsdatabase.com/wordsearch.php?query=sunscreen.