Note: this is not a summary. For a summary, read our quick guide on all things related to sunscreen safety. Otherwise, enjoy!
Is sunscreen killing corals? No one is really sure. What is certain is that select ingredients in sunscreen – Oxybenzone, Benzophenone-1, Benzophenone-8, OD-PABA, 4-Methylbenzylidene camphor, 3-Benzylidene camphor, nano-Titanium dioxide, nano-Zinc oxide, Octinoxate, Octocrylene – cause coral bleaching, which happens to corals when they are under stress. Coral bleaching occurs when corals expel the algae with which they live in symbiotic relationship. If coral bleaching is temporary, the coral can recover. If bleaching is extended, then the coral is more likely to die.
If these ingredients lead to coral bleaching, and coral bleaching increases the chance of coral death, then how are scientists unsure of the effects? That’s because there are a lot of confounding variables. First, many things lead to coral bleaching, including temperature fluctuations caused by climate change and increased pollutants. Second, it’s hard to estimate how much sunscreen actually gets into the ocean and stay near corals, as opposed to getting carried further into the ocean (“the solution to pollution is dilution” sort of thinking).
Many people argue that focusing on the effects of sunscreen ingredients on corals is like cleaning a table when the house is burning down. The main issues to our corals dying are climate change and pollutants. That being said, climate change and controlling pollutants require mass cooperation, likely on the governmental level; whereas we as individuals can choose what sunscreen to wear.
As noted above, zinc oxide and titanium oxide are listed as possible coral bleaching agents, but the “nano” prefix is important. Nano-particles are relatively recent and controversial inventions in skincare. Formulators take ingredients and break them down to ever-smaller particles, so they absorb better into the skin. Depending on the ingredient, some nano-particles can be too small and have unintended consequences.
Nano-zinc oxide and nano-titanium dioxide make it easier for your skin to absorb them, so you don’t have as much of a white cast; but because their properties change as the size becomes smaller, its effects in the body are less understood. That’s not to say they are dangerous for you; in fact, existing (limited) research appears to show that they aren’t absorbed into the body in significant quantities. We just aren’t as sure as for regular zinc oxide and titanium dioxide. If you want to avoid nano-particles in your mineral sunscreen, many brands now label their sunscreens “non-nano,” though brands’ definition of what “non-nano” actually means differs.For the purposes of this post, the more ugly white stuff your mineral sunscreen leaves after application, the less likely it’s to harm the corals.