This post can also be found on the Blonde Biologist
Paige: During my recent trip to Hawaii I was struck with surprise when I saw posters in many shops and airports urging the importance of using a coral-reef safe sunscreen. In my typical manner I was skeptical at first but once I saw the pictures of damaged coral and read Rachel’s Instagram post I decided to do some research to figure out exactly what is going on. As consumers, it’s important to know the full impact of our cosmetic products and sunscreen is a prime example of where attention needs to be given. For this post, I collaborated with Rachel from the Blonde Biologist, who is currently an environmental biologist living in Honolulu, HI to understand the full impact that sunscreen is having on our world’s coral reefs.
Rachel: Corals are the backbone of marine reef ecosystems, which rival only tropical rainforests in their biodiversity. Coral reefs provide shelter and food for an enormous number of organisms, regulate carbon dioxide levels and the pH of the oceans, protect the shorelines against erosion and flooding, and support million-dollar tourism industries and fisheries across the world. Unfortunately, certain sunscreen ingredients are greatly impacting the health of coral reefs through direct contact (i.e. surfing, snorkeling, swimming) and indirect contact (wastewater streams from showering).
Paige: The primary ingredient to blame for the damage sunscreen is causing is oxybenzone, which will be the focus of my investigation in this post. Oxybenzone is a chemical sunscreen agent that is commonly used in sunscreen formulas to help prevent UVA and UVB waves from damaging the skin. However, oxybenzone is a somewhat weak chemical absorber and is primarily used as a photostabilizer in formulas. This is why you will rarely see oxybenzone listed as the only active ingredient in sunscreens.
Although this ingredient is listed as safe for use by the FDA (for up to 6% concentration), there are currently many studies examining the long term safety effects of this ingredient. While the health effects are still under investigation (more evidence is needed to solidify anything) the effects of oxybenzone on coral reef have been proven and is an issue that needs more attention.
Rachel: A 2008 study investigated the effects of oxybenzone on four coral reef environments in the Pacific Ocean, Atlantic Ocean, and the Indian Ocean. Researchers found that corals exposed to any concentration of oxybenzone-containing sunscreen, no matter the brand or UV filter, demonstrated bleaching. The study also found that factors like warmer water temperatures caused bleaching to occur more quickly. A 2016 study investigated the effects of oxybenzone on coral reef environments in Hawaii and the US Virgin Islands, and the results were alarming. The study found that use of oxybenzone-containing sunscreen in these areas led to death and deformity of both adult and larval corals. It also showed that oxybenzone is a phototoxicant, meaning the negative effects are greatly magnified in the light. In fact, the study found that the lethal concentration of oxybenzone for coral larvae is more than five times greater when exposed to light. Unfortunately, daylight is when sunscreen concentrations washing off in the ocean are higher from swimmers and surfers.
Rachel: A coral’s life in a healthy reef system occurs as follows. Corals metamorphose into their recognizable mature adult form from an extremely different microscopic juvenile form. Mature coral adults release their eggs and sperm into the open water where fertilization takes place. Coral larvae are microscopic and covered in tiny hairs (cilia) that help them move along with the current to find a hard substrate to settle on and start their metamorphosis. Once the planulae have latched onto a substrate, their shape begins to change into a polyp form and their main focus is secreting calcium carbonate to create a protective skeleton around their soft polyp bodies. The calcium carbonate skeleton creates more surface area for other larvae to settle on and develop, as well, creating a larger reef system. The polyps strike a deal with algae called zooxanthellae; if the polyps provide a safe haven for the zooxanthellae within their calcium skeleton, the zooxanthellae provide energy for the polyps via photosynthesis. A symbiotic relationship ensues, the coral continues to grow into sexually mature adults, and the cycle continues.
Oxybenzone affects coral at critical points in its life cycle. Researchers have discovered that the introduction of oxybenzone into a coral reef environment causes coral bleaching or the rejection of zooxanthellae in adults and developing polyps, endocrine disruptions in juveniles, and DNA alterations in adults. If corals exposed to oxybenzone eject most of the zooxanthellae from their polyp bodies, the coral loses a significant amount of energy. The pale white color of the coral after ejection of zooxanthellae occurs because the algae’s photosynthetic pigments normally give the coral its bright color. If the coral is unable to recover from the oxybenzone’s forced evacuation of zooxanthellae and regain its symbiotic algae, the coral will die. The second offense of oxybenzone against corals is endocrine disruption as settled juveniles are beginning to develop their calcium carbonate skeletons. Exposure to oxybenzone causes the larvae to ramp up production of calcium carbonate, eventually trapping themselves inside their own thickened skeletons. Oxybenzone’s third documented offense against corals is mutagenic alterations to adult DNA sequences, preventing the coral cells from carrying out DNA replication or transcription. Without these two important processes, the adult corals lose the ability to reproduce. Oxybenzone essentially renders adult corals sterile, and any reproduction that does manage to occur results in deformed larvae that are unable to continue development for reasons mentioned previously.
Paige: As I mentioned earlier, oxybenzone is a chemical sunscreen agent, this means that it acts as a chemical UV absorber. Essentially, these type of ingredients absorb the energy from the UV light and release the energy back out of the skin (at a lower energy level) without allowing it to fully penetrate and cause damage. Chemical sunscreen ingredients require more time after application to absorb into the skin than physical sunscreen ingredients. This is because physical sunscreen ingredients, like zinc oxide or titanium dioxide, reflect UVA and UVA exposure by sitting on the top levels of our skin. This is the type of sunscreen that causes a heavy white cast on the skin and is responsible for the classic lifeguard nose.
Oxybenzone’s mechanism of action is simply to act as a UV filter and protect the skin. Since it has UV light absorbing abilities, this causes it to react very strongly with extra light exposure (i.e. when you’re having a sunny beach day). So this mechanism of action, though it allows the ingredient to be effective in sunscreen formulas, has a negative effect on the coral due to its positioning in the direct sunlight. As Rachel stated earlier, this is what causes oxybenzone to act as a phototoxicant towards the coral. Additionally, a 2008 study showed that the primary method of exit for this ingredient from our body is through urine, which eventually will find its way back into the ocean. Further showing the importance of using sunscreens without oxybenzone.
So, what’s a consumer to do?
Rachel: The number one method to prevent exposure of sunscreen chemicals to coral reefs is to avoid sunscreen altogether. While you can wear long sleeves and pants, hats, and other SPF protective gear and stay in a shaded area, avoiding sunscreen completely isn’t always feasible. I would turn into a crispy red lobster here in Hawaii without any sunscreen! In that case, look for the label “reef-safe” or “reef-friendly” on sunscreen. Zinc oxide and titanium oxide are common alternatives that have not been shown to harm corals. Remember that even if you’re not a surfer/snorkeler/swimmer and you avoid direct contact with the ocean, all that sunscreen you lathered on to avoid sunburns at the baseball field still ends up in the ocean eventually from your shower drain.
Paige: Using a reef friendly sunscreen is the easiest way to help marine life out. However, we understand that it may be hard to make this transition completely especially if you’re landlocked, we’re both from the Midwest we understand the feeling. So at minimum make the effort to buy a coral reef safe sunscreen when you’re on a beach, lake or even just laying in the sand (everything ends up in the ocean).
Rachel: Without coral reefs, there are no tropical fish, sea turtles, or sharks. Thanks for doing your part to keep our oceans healthy and beautiful!
Paige: We really hope that this post helped you understand the impact our sunscreens have on the ocean and what you can do to help out marine life!
Below are more links to read if you’re curious about this topic and/or want to find some reef friendly sunscreens, enjoy!
Read more about environmental biology (and get lots of pretty Hawaii pics) at the Blonde Biologist: https://theblondebiologist.com/about/