Sunscreen’s oxybenzone is converted to phototoxin, posing a threat to vulnerable coral reefs

Oxybenzone, a popular sunscreen ingredient, can be converted from a UV blocker to a powerful phototoxin inside cells of anemone and coral, according to new experiments conducted by Djordje Vuckovic and colleagues. These phototoxins, which make anemones more susceptible to damage under sunlight, may help explain why oxybenzone-based sunscreens are harmful to bleached coral reefs, the researchers say. In some places with lots of swimming tourists, this type of sunscreen has been banned to prevent reef damage, although scientists were unsure about the exact mechanism of damage. Now, the new information from Vuckovic et al. could help guide the development of sunscreen formulas with less potential to metabolize into phototoxins. In their experiments with sea anemone and mushroom coral, the researchers found that oxybenzone is metabolized into a phototoxin in the animals’ cells by the addition of glucose. In the anemone, symbiont algae sequester most of this phototoxin, but removing the protective algae—as is the case with coral “bleached” by warming oceans—allowed the phototoxin to accumulate and cause damage. As Vuckovic notes in a related Science podcast, “the finding that oxybenzone sunscreen is more toxic to these bleached anemones could suggest that it’s also more toxic to bleached corals, and that it would actually exacerbate these negative effects of warming … in the areas where you have human activity around.” A related Perspective by Colleen Hansel discusses these findings. The related podcast will be available at https://www.science.org/podcasts on Thursday, May 5.