As the summer months approach it is more important than ever to be taking care of our skin and being diligent about sun protection. 

However, studies have demonstrated a negative correlation between sunscreen exposure and coral reef health. ^[1]1.McCoshum, Shaun M., Alicia M. Schlarb, and Kristen A. Baum. “Direct and Indirect Effects of Sunscreen Exposure for Reef Biota.” Hydrobiologia 776, no. 1 (August 2016): 139–46. … Continue reading For those who enjoy spending time in or around the ocean, navigating this issue can be a little confusing. How do we protect our skin and ocean ecosystems at the same time?  

Join us today as we attempt to decipher the ongoing battle between reef health and skin protection, debunking “reef-safe”, and looking at sun protection alternatives, just in time for the warmer months! 

What are Zooxanthellae?

First, let’s discuss the symbiotic dinoflagellates that live inside corals called zooxanthellae (pronounced ZOH-uh-zan-THEL-ay). We are starting here because these organisms are critical to coral persistence and reef health and are the first to bear the brunt of both anthropogenic (human-caused) and natural disturbances. In this symbiotic relationship the corals give zooxanthellae a protected environment to live and in return zooxanthellae photosynthesize and transfer around 90% of the organic material produced directly to the coral tissue. ^[2]2. Fel, Jean-Pierre, Catherine Lacherez, Alaa Bensetra, Sakina Mezzache, Eric Béraud, Marc Léonard, Denis Allemand, and Christine Ferrier-Pagès. “Photochemical Response of the Scleractinian … Continue reading ^[3]3.US Department of Commerce, National Oceanic and Atmospheric Administration. “Zooxanthellae…What’s That – Corals: NOAA’s National Ocean Service Education.” Accessed May 30, 2022. … Continue reading ^[4]4.LaJeunesse, Todd C. “Zooxanthellae.” Current Biology 30, no. 19 (October 2020): R1110–13. https://doi.org/10.1016/j.cub.2020.03.058.

How is the coral-zooxanthellae relationship established? In some cases, zooxanthellae are transferred from the parent coral directly to its offspring (this is known as vertical transmission), and in others coral larvae are inhabited by free-floating zooxanthellae from their surrounding environment (this is known as horizontal transmission). ^[5]5. Padilla-Gamiño, Jacqueline L., Xavier Pochon, Christopher Bird, Gregory T. Concepcion, and Ruth D. Gates. “From Parent to Gamete: Vertical Transmission of Symbiodinium (Dinophyceae) ITS2 … Continue reading

Stress can cause these zooxanthellae to expel themselves from the coral structure, causing the coral to undergo a ghostly transformation and bleach. 

What is Coral Bleaching?

Bleaching describes the temporary or permanent loss of the coral’s zooxanthellae as the result of a natural or anthropogenic stressor which can subsequently lead to nutrient starvation. Hard corals, unlike other members of the phylum Cnidaria (which also include jellyfish and anemones), secrete calcium carbonate, a chemical compound that gives corals their white skeletal structure. Following the expulsion the zooxanthellae (which are also responsible for giving corals their color) the calcium carbonate skeleton is left exposed. ^[6]6.Glynn, Peter W. “Coral Reef Bleaching: Facts, Hypotheses and Implications.” Global Change Biology 2, no. 6 (1996): 495–509. https://doi.org/10.1111/j.1365-2486.1996.tb00063.x. ^[7]7. Raffa, Robert B., Joseph V. Pergolizzi Jr., Robert Taylor Jr., Jan M. Kitzen, and for the NEMA Research Group. “Sunscreen Bans: Coral Reefs and Skin Cancer.” Journal of Clinical Pharmacy and … Continue reading

A bleached coral is not necessarily dead but it is a clear indication that something is wrong with the reef ^[8]7. Raffa, Robert B., Joseph V. Pergolizzi Jr., Robert Taylor Jr., Jan M. Kitzen, and for the NEMA Research Group. “Sunscreen Bans: Coral Reefs and Skin Cancer.” Journal of Clinical Pharmacy and … Continue reading such as a dramatic change in temperature or salinity (the concentration of dissolved salt in a body of water), ^[9]8. Sparks, Donald L. “10 – The Chemistry of Saline and Sodic Soils.” In Environmental Soil Chemistry (Second Edition), edited by Donald L. Sparks, 285–300. Burlington: Academic Press, … Continue reading or the introduction of a disease, pollutant, or chemical.^[10]7. Raffa, Robert B., Joseph V. Pergolizzi Jr., Robert Taylor Jr., Jan M. Kitzen, and for the NEMA Research Group. “Sunscreen Bans: Coral Reefs and Skin Cancer.” Journal of Clinical Pharmacy and … Continue reading

Bleached corals are not able to obtain the sufficient nutrients they need to support growth and reproduction and are also not as able to defend themselves against competing species. ^[11]7. Raffa, Robert B., Joseph V. Pergolizzi Jr., Robert Taylor Jr., Jan M. Kitzen, and for the NEMA Research Group. “Sunscreen Bans: Coral Reefs and Skin Cancer.” Journal of Clinical Pharmacy and … Continue reading

Sunscreen and Coral Reef Health

Now, let’s get into the reason you are all here.

Depending on the ingredients used, sunscreens can be classified as chemical absorbers or physical blockers, ^[12]9.Mori, Shoko, and Steven Q. Wang. “50 – Sunscreens.” In Comprehensive Dermatologic Drug Therapy (Fourth Edition), edited by Stephen E. Wolverton, 565-575.e2. Elsevier, 2021. … Continue readingeach designed with the purpose to protect skin from solar radiation by reflecting, scattering, or otherwise deflecting UV rays to avoid absorption. ^[13]10.Parrado, Concepción, Yolanda Gilaberte, Neena Philips, Angeles Juarranz, and Salvador Gonzalez. “Chapter 34 – Fern Extract, Oxidative Stress, and Skin Cancer.” In Cancer (Second … Continue reading

It has been estimated between 6,000-14,000 tons of sunscreen are released into coral reef ecosystems each year. ^[14]11. Downs, C. A., Esti Kramarsky-Winter, Roee Segal, John Fauth, Sean Knutson, Omri Bronstein, Frederic R. Ciner, et al. “Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone … Continue reading Contamination of these UV filters are not limited to coral reefs and have been detected in surface waters across the globe as far up as the Arctic. ^[15]12. Adler, Brandon L., and Vincent A. DeLeo. “Sunscreen Safety: A Review of Recent Studies on Humans and the Environment.” Current Dermatology Reports 9, no. 1 (March 2020): 1–9. … Continue reading

The UV filters and blockers in sunscreens, while technically not permanent pollutants, are often considered “pseudo-persistent pollutants”. Because the site of contamination is constantly being renewed, the organisms in that environment are receiving constant exposure. ^[16]11. Downs, C. A., Esti Kramarsky-Winter, Roee Segal, John Fauth, Sean Knutson, Omri Bronstein, Frederic R. Ciner, et al. “Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone … Continue reading

Not only do certain sunscreen chemicals cause the expulsion of zooxanthellae, there is also research to suggest that some of these ingredients have the potential to bioaccumulate (build up in the body) in marine organisms, undergo photodegradation (decomposition by light) and create phototoxins, and increase viral infections in coral species. ^[17]13. Danovaro, Roberto, Lucia Bongiorni, Cinzia Corinaldesi, Donato Giovannelli, Elisabetta Damiani, Paola Astolfi, Lucedio Greci, and Antonio Pusceddu. “Sunscreens Cause Coral Bleaching by … Continue reading 

Because sunscreens often contain numerous chemical compounds it can be difficult to decipher which ingredients specifically are causing ecological damage. A study conducted by Danovaro et al. in 2008 looked at common chemical compounds used in sunscreens, and of those tested, found that many of the common chemicals used (even at low concentrations) caused corals to bleach entirely. ^[18]13. Danovaro, Roberto, Lucia Bongiorni, Cinzia Corinaldesi, Donato Giovannelli, Elisabetta Damiani, Paola Astolfi, Lucedio Greci, and Antonio Pusceddu. “Sunscreens Cause Coral Bleaching by … Continue reading

The Top 7 Ingredients to Avoid:

1. Oxybenzone  
   • Other names: Benzophenone-3, BP-3 
2. Avobenzone 
   • Other names: Butyl methoxydibenzoylmethane
3. Octyl Methoxycinnamate 
   • Other names:Octinoxate, ethylhexylmethoxycinnamate
4. Octocrylene
5. Octyl salicylate
   • Other names: ethylhexyl salicylate
6. Enzacamene
   • Other names: 4-methylbenzylidene camphor
7. Butylparaben

Avoid these popular brands:

1. Alba Botanica Hawaiian Sunscreen
2. Aveeno Sunscreen Broad Spectrum Face Lotion SPF 60
3. Banana Boat Sport Ultra Lotion 
4. Glossier Invisible Shield
5. Hawaiian Tropic Silk Hydration Weightless Lotion SPF 50
6. Neutrogena Beach Defense® Water + Sun Protection Sunscreen Lotion Broad Spectrum SPF 30 
7. SunBum Original SPF 50 Sunscreen Lotion
8. Supergoop PLAY Everyday Lotion SPF 50 with Sunflower Extract

It is important to note that a sunscreen can be considered “reef-safe” or “reef-friendly” by brands if they do not contain oxybenzone or octinoxate but as we have just learned, those are not the only chemicals that damage coral reefs. It is incredibly important to read the active ingredients in sunscreens, even if they are labeled “reef-safe” or “reef-friendly.

Try these brands instead:

1. Stream2Sea Every Day Active Mineral Sunscreen
2. ALL GOOD Kid’s Natural Sunscreen Spray 
3. Blue Lizard Sensitive Mineral Sunscreen

Is Zinc a Better Alternative?

Oftentimes zinc is advertised as an alternative to chemical sunscreens, better for your health and better for the environment, is this true? Let’s look into it. 

A study by Fel et al. in 2019 found coral exposure to zinc oxide nanoparticles (ZnO-NP)  caused a significant decrease in the coral’s photosynthetic capabilities and induced coral bleaching. The same study also found ZnO had the ability to disrupt the coral’s lipid membrane (this separates the inside of the organism from its external environment) as well as increase the concentration of bacteria in the surrounding water. ^[19]2. Fel, Jean-Pierre, Catherine Lacherez, Alaa Bensetra, Sakina Mezzache, Eric Béraud, Marc Léonard, Denis Allemand, and Christine Ferrier-Pagès. “Photochemical Response of the Scleractinian … Continue reading

Additionally, a study conducted in 2018 by Corinaldesi et al. produced similar results and found that the overall expulsion and damage of zooxanthellae was significantly greater in corals exposed to zinc oxide nanoparticles (ZnO-NP) than those exposed to another inorganic blocker, nano-titanium dioxide (TiO2-NP). Additionally, surrounding waters exposed to zinc oxide were more contaminated with viruses that could threaten coral survival, compared to nano-titanium dioxide where none were present. ^[20]12. Adler, Brandon L., and Vincent A. DeLeo. “Sunscreen Safety: A Review of Recent Studies on Humans and the Environment.” Current Dermatology Reports 9, no. 1 (March 2020): 1–9. … Continue reading

Now, if  this is the case, why is zinc oxide used in “reef-safe” sunscreens? Turns out it all comes down to the size of the zinc oxide particle. As mentioned previously, nanoparticle zinc oxide has been shown to be incredibly harmful to reefs and has even been classified as “hazardous to aquatic environments” according to the United Nations Globally Harmonized System of Classification and Labeling of Chemicals (GHS). ^[21]2. Fel, Jean-Pierre, Catherine Lacherez, Alaa Bensetra, Sakina Mezzache, Eric Béraud, Marc Léonard, Denis Allemand, and Christine Ferrier-Pagès. “Photochemical Response of the Scleractinian … Continue reading Now, enter non-nanoparticle zinc oxide. Compared to its nanoparticle counterpart, non-nanoparticle zinc oxide is larger, won’t penetrate through your skin, is still effective against protection from UVA/UVB rays, all while being less harmful to coral reef ecosystems overall. 

The bad part? Because of its size, non-nanoparticle zinc oxide will likely leave a white tint behind after sunscreen application, while nanoparticle zinc oxide will not. This is just my opinion, but a white tint seems like a small price to pay when the alternative is reef ecosystem destruction… Just saying. 

Next Steps: 

So now that we have this information what should we do with it? Here are a few closing tips. 

1. Be conscious about the sunscreen you buy and the environments that you wear them in. 
2. Avoid sunscreens containing the 7 scary ingredients mentioned above.
3. Nanoparticle zinc oxide is BAD, Non-nanoparticle zinc oxide is OKAY. 
4. If you cannot get behind the white cast left from mineral sunscreen containing zinc oxide and titanium dioxide, opt for wearable sun protection like hats, sunglasses, and sun shirts. 
5. Help educate those around you! Time with friends and family at the beach or hanging out by the water is the perfect opportunity to tell people what you’ve learned from this blog. Remember to save judgement and offer alternatives.

Helena Milazzo

Founder and CEO of LegaSea Ecology LLC

Learn More About Helena