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Why are some Sunscreens Labelled as “Reef-Safe”?

Scientific evidence that sunscreens damage coral reefs are shady.

“Reef-Safe” on the label intends to inform the consumer that the product does not contain ingredients that may harm coral reefs. That claim, though, must be viewed with a degree of skepticism.

It may surprise you to find out that coral is actually an animal. A very tiny one. These little creatures live together in a colony and each one secretes an exo-skeleton made of calcium carbonate (limestone). It is these skeletons that we see, giving the impression that coral is some sort of stone. Coral has a symbiotic relationship with plant-like organisms called algae that reside within the coral. Algae use carbon dioxide released by the coral’s respiration for photosynthesis. This then supplies the coral with oxygen and the nutrients it needs for growth. Like all living things, eventually coral dies, leaving behind a limestone deposit that makes up coral reefs.

When corals are stressed due to temperature change, lack of nutrients, or exposure to toxins, they expel the green algae causing them to turn white. This is known as “bleaching.” Without algae, coral will eventually die.

Several preliminary studies have implicated octinoxate, oxybenzone, 4-methylbenzylidene camphor (4-MBC), and some other UV filters found in sunscreens as potential culprits for coral bleaching. These findings resulted in several sunscreen bans, as well as the appearance of “reef-safe” labelling on many sunscreens. However, critical reviews have cleared the water, concluding that the implication of sunscreens in coral damage lacks sound scientific evidence. Reviewers suggest that the studies in which the harmful effects of sunscreens on coral have been observed, have used concentrations of chemicals that far exceed true environmental concentrations found near reefs. Additionally, the conditions in these studies (concentrations used, exposure times, test duration, biological endpoints) varied greatly, further weakening their findings.

More extensive research to investigate the role of sunscreens on coral toxicity under conditions that are actually encountered in the ocean is called for. In a 2021 review, scientists outline a standardized testing method to better evaluate sunscreen toxicity as it pertains to coral reefs. Currently, the National Academies of Sciences, Engineering, and Medicine is conducting a more thorough evaluation of the potential toxicity of sunscreens to aquatic ecosystems, while also evaluating the public health implications.

Presently there is no reliable indication that sunscreen ingredients pose a threat to coral except under laboratory conditions. As Terry Hughes, marine biologist and leading expert on coral bleaching, puts it, “sunscreen does not cause coral bleaching, except in a test tube”. Hughes highlights that the lead culprit of coral bleaching is global warming as a result of climate change.

For the most part, “reef safe” labels are advertised on sunscreens that do not contain octinoxate, oxybenzone, or 4-MBC - the ingredients targeted by the preliminary studies. The term “reef-safe” is not defined or regulated, so companies can freely label their products as such. A clearer definition of “reef-safe” is necessary, but as we have seen, sunscreen ingredients are not the main cause of unhealthy reefs.

Of course, if you are visiting destinations where there are bans on certain ingredients, you can take other precautions to reduce the amount of sunscreen that ends up in the water. Tourist-heavy coastal regions have been found to accumulate higher levels of sunscreen in their waters, so it’s a good idea to take precautions if you are in these areas. Start by supplementing your sun-safety approach by finding shade, wearing UV-protective clothing, and staying indoors while the sun’s rays are most harsh (11am – 3pm). If you are out and about, you should be using a lotion sunscreen instead of spray-on alternatives, since lotion allows for a more controlled application. Finally, opt for a “water-resistant” sunscreen so that it stays put when you go for your swim.

Just remember, there are plenty of factors involved in the degradation of coral reefs and whatever role sunscreens may play is likely to be minor.


Cat Wang recently graduated from McGill University with a Bachelor of Science (BSc) degree in the anatomy and cell biology program and is currently deciding on a Master’s program.

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