In a recent issue of ChemistryWorld, an online publication of the Royal Society of Chemistry, a revealing article on work first published in Science describing how the combination of the UV sunscreen active ingredient oxybenzone and UV light together produce something that is toxic to corals reefs.

Researchers (paywall) at Stanford University found in their sea anemone model studies that in the presence of UV light, oxybenzone is modified by the attachment of glucose, forming a water soluble glycoside conjugate. This is a not an uncommon event in metabolism. The oxybenzone-glycoside conjugate was found to be a potent photo-oxidant and quite toxic to the algal symbionts of coral. A methoxy analog proved to be much more potent.

Benzophenones, of which oxybenzone is a variety, are well known photosensitizers and photoinitiators.

Locations like Hawaii and Palau have banned the sale of oxybenzone-containing sunscreens due to the harm they cause to coral reefs.