Get Cancer For Coral

When going to the beach, the one thing no one forgets is sunscreen. It is the saving grace of all fair skinned homosapiens who have to apply religiously after the ocean washes it all off their body. However,there is a problem that few people think about. What happens to all that sunscreen that gets washed off your body? Is it harmful to coral reefs and the marine life they support?

Coral and sponges

Coral reefs make up less than 1% of the ocean floor but are home to an estimated one million species of fish, invertebrates, and algae (Gilbert et al. 2009). The actual corals belong to the phylum Cnidaria and are made up of animals called polyps. Zooxanthellae or symbiotic algae, live in the polyps and provide the coral with food through photosynthesis. So already we can see some problems sunscreen might have on the lives of coral. If sunscreen from your body washes off and gets on the coral that have to receive sunlight in order to produce food, then the coral will not be able to get the proper sunlight, which will lead to death. Over 60% of coral reefs are under threat from a variety of sources including marine pollutants (Gilbert et al. 2009). You may not think that sunscreen amasses for a lot of marine pollutants, but 10% of the coral in danger is just because of sunscreen-induced bleaching (Than 2008). In 2005 sunscreen product sales reached over half a billion dollars (Shaath and Shaath 2005). The United States National Park Service claims that 4,000 to 6,000 tons of sunscreen enters reef areas annually (Than 2008). Unfortunately these concentrations of sunscreen do not spread out evenly over the entire ocean and it is estimated that 90% of tourists are concentrated on only 10%  of the world’s reefs (Gilbert et al. 2009). That means reef areas with high tourist rates get much more exposure to sunscreen than most.

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Tourist destroying coral and spreading sunscreen all around the reef.

Interestingly, some of the chemicals in sunscreens interact with the coral in strange ways. One study found that sunscreen promoted coral bleaching by promoting viral infections (Danovaro et al. 2008). In the study, even very low concentrations of sunscreen (i.e., 10 µL/L), was enough to cause large amounts of coral mucus (composed of zooxanthellae) to be released within 18-48 hours (Danovaro et al. 2008). In hard corals, low concentration amounts of 10 µL/L caused complete bleaching within 96 hours (Danovaro et al. 2008). The controls used throughout the experiment didn’t show any change, but the experimental groups bleached faster when larger quantities were used (Danovaro et al. 2008). Further experiments were done on seven specific compound found in most common sunscreens in order to better understand the exact cause of coral bleaching. They found that butylparaben, ethylhexyl- methoxycinnamate, benzophenone-3 and 4-methylbenzylidene camphor caused complete bleaching even at very low concentrations (Danovaro et al. 2008). However, octocrylene, ethylhexyl salicylate, and 4-tert-butyl-4-methoxydibenzoylmethane, and the solvent propylene glycol, which are all common ingredients in sunscreen, had little or no effects on the coral (Danovaro et al. 2008). They also found that after hard corals were exposed to sunscreen, the seawater surrounding the coral branches increased in viral abundance significantly and even reached values that were fifteen times greater than the controls (Danovaro et al. 2008). The samples from all around the world showed that latent infections are common in symbiotic zooxanthellae. Once the coral is exposed to sunscreen, the lytic cycle in the viruses are activated (Danovaro et al. 2008). They believe that sunscreen among other things like pesticides are both contributing to promoting the lytic cycle in viruses that leads to coral bleaching.

Further studies have been done with Benzophenone-2 (BP-2), another common ingredient in sunscreen, to try and pin down the more specific effects that it has on coral. They found that BP-2’s effects were more severe in the light than in the dark (Downs et al. 2014). This surprised me since at Trek we were told that most coral are nocturnal. But in the dark and light, BP-2 caused coral planulae to change from a motile planktonic state to a more deformed and sessile state (Downs et al. 2014). However, in the light, BP-2 caused necrosis in the coral’s epidermis and gastrodermis layers while in the dark it caused autophagy and autophagic cell death (Downs et al. 2014). What is really amazing is how little amount of BP-2 causes this kind of reaction. The LC50 of BP-2 in light for 24 hour exposure was 165 parts per billion and in the dark 548 parts per billion (Downs et al. 2014). It doesn’t take a whole lot of sunscreen at all for it to cause damage to the coral.

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Zooxanthellae in coral

So what can we do? Probably the best thing for the coral reefs is to just leave them alone. Whenever humans get involved, it typically means that the environment suffers. But since this will never happen, the next best thing is to educate people who are going to be swimming around the reefs to not wear sunscreen. This sounds like a bad idea, but there are other options besides sunscreen that will keep you protected. The United States National Park service recommends covering up in rash guards and other similar clothing. Sorry this won’t give you a tan, but it will protect you and the coral reefs from harm.

So what have we learned? Sunscreen can cause harm to coral in a number of different ways. First, it can block the sun which is needed for the coral to get their energy. Second, a lot of chemicals in sunscreen lead to coral bleaching due to them activating the lytic cycle in viruses. Third, it doesn’t take a whole lot of sunscreen to cause these harmful effects and the chemicals, specifically BP-2, have worse effects in light. Lastly, this is an easy fix if we want to keep our coral reefs, just cover up with clothes.


Blitz, J. B., & Norton, S. A. (n.d.). Possible environmental effects of sunscreen run-off. Journal of American Dermatology, 59, 897–898. doi:10.1016/j.jaad.2008.06.013

Danovaro, R., Bongiorni, L., Corinaldesi, C., Giovannelli, D., Damiani, E., Astolfi, P., … Pusceddu, A. (2008). Sunscreens cause coral bleaching by promoting viral infections. Environmental Health Perspectives. doi:10.1289/ehp.10966

Downs, C. A., Kramarsky-Winter, E., Fauth, J. E., Segal, R., Bronstein, O., Jeger, R., … Loya, Y. (2014). Toxicological effects of the sunscreen UV filter, benzophenone-2, on planulae and in vitro cells of the coral, Stylophora pistillata. Ecotoxicology, 23(2), 175–191. doi:10.1007/s10646-013-1161-y

Gilbert, D. T., & Ferry Center, H. (2009). Protect Yourself, Protect The Reef! Discovering an underwater wonderland.

Than, K. (2008). Swimmers’ Sunscreen Killing Off Coral. National Geographic. National Geographic Society, n.d. Web.

Shaath NA, Shaath M. 2005. Recent sunscreen market trends. In: Sunscreens, Regulations and Commercial Development (Shaath NA, ed). Third ed. Boca Raton, FL:Taylor & Francis, 929–940.


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