Written by Sofia Perez

Edited by Matthew Tietbohl

On a hot summer day (or every day if you follow dermatological advice), you squeeze out a tiny lump of creamy white sunscreen onto your hand. Then you spread it all over your face, lamenting how pale it makes you look, and promptly move on to the next big thing in the day. 

Just like the ingredients in your food, the ingredients in your sunscreen are also going into your body. This includes chemicals, such as octinoxate, 1-6% of which will be absorbed into the skin and excreted in the urine. Studies have even shown it to be present in blood and breast milk too. However the presence of sunscreen’s ingredients does not end with the human body. 

Now imagine that the hot summer day is drawing to an end and that layer of sunscreen, sweat, and other gross particulate matter is starting to feel uncomfortable. What do you do now? Most people would shower. Now the problem is solved, and poof all the nasty chemicals on your skin disappear down the drain and you smell like eucalyptus shower gel. But nothing ever disappears… 

From the drain of your shower, the unique concoction of chemicals in sunscreen, makeup, shampoo, hair dye, lotion, etc. are washed into a bigger mix of natural and unnatural compounds from your neighbors’ drains and the rest of the world. 

So where do all our cosmetics end up flowing? The complete answer is long, but let’s focus on one ecosystem for the time being: coral reefs. Furthermore, let’s only look at one ingredient: octinoxate. This vast oversimplification must be forgiven, however, as coral reefs are one of the most biodiverse and economically productive habitats on the planet. (Thank you for forgiving me. I knew you would understand.)

Why octinoxate though? Besides the fact that it is the most widely-used UVB-absorber in conventional chemical sunscreen and works to keep costs down, its secret identity is also that of a “ubiquitous environmental contaminant”.  While this is clearly a disturbing title for something that has been found in human urine, blood, and breast milk, it also spells disaster for the aforementioned coral reefs. 

To explain the most common side effects of octinoxate exposure, it’s important first to understand a concept known as genotoxicity. A genotoxin is a toxin which damages genetic material and can give rise to genetic mutations. Importantly, contrary to what superhero movies would suggest, genetic mutations are a dangerous business. While on the off chance you go from normal-human to Spiderman-human, the reality is usually not so kind. When foreign chemicals mess around with DNA, the result is usually akin to what you would get if you brought down a sledgehammer on a Rolex. Yes, I suppose there is a small chance it will work better afterwards, but let’s not forget how absolutely minute that chance really is.

Because octinoxate is a genotoxin, it has these kinds of effects on fish and invertebrates, disrupting the expression of genes which play a role in hormonal regulation, bringing down the proverbial sledgehammer on their metabolism. In coral reefs, studies have shown that octinoxate even induces coral bleaching, in which the symbiotic algae that live in unison with coral polyps flee, giving the coral no energy to carry on. However, because most research for this compound is conducted within a controlled environment inside a lab rather than in situ, it must be highlighted that these findings should be taken with a pinch of salt. Nonetheless, where there are research gaps, there are new discoveries! Hopefully this will encourage a new cohort of researchers to explore this topic a bit more.  

So exactly how much octinoxate is in our reefs? After all, it’s thought that about 14,000 tonnes of sunscreen wash into the ocean every year. On average, that’s the same weight as one hundred blue whales. Once this spreads out over all the marine and freshwater environments from the Arctic Circle to the equator in which it has been found, this “ubiquitous environmental contaminant” can be found in up to more than 10 parts per billion. This means that for every one gram of water in coral reefs, there can be up to ten billionths of octinoxate. To most people this might seem like a negligible amount, but for compounds as powerful as this one, it’s nothing to sneeze at. Moreover, bioaccumulation can cause it to be magnified in organisms higher up the food chain, causing more significant effects. You might compare such a molecule to a celebrity. They are only one person, but their presence is enough to change the dynamics of millions of other lives. 

So we have established that octinoxate has a dark side. It is for this reason that it is listed on the European watch list of substances that may pose significant risk to aquatic environments and that, while approved in the U.S., the FDA restricts the strength of formula to a maximum of 7.5% octinoxate concentration. In Hawaii, lawmakers even went as far as to completely ban the use of sunscreens containing octinoxate due to a 2015 study linking it with coral bleaching. 

Still, it must be stressed that there are many other compounds with adverse effects on the environment, such as oxybenzone, which is even more toxic than octinoxate. In addition, there are many more ecosystems which are negatively impacted by the products we use to make our own skin and hair look healthier. 

Bibliography

Abelvik-Lawson, Helle. “Chemicals in Suncream Are Destroying Coral Reefs.” Greenpeace UK, 17 Aug. 2021, http://www.greenpeace.org.uk/news/most-suncream-is-terrible-for-ocean-life-heres-how-to-stay-safe-in-the-sun-without-damaging-the-environment/. Accessed 7 Sept. 2021.

Duale, Nur, et al. “Octyl Methoxycinnamate Modulates Gene Expression and Prevents Cyclobutane Pyrimidine Dimer Formation but Not Oxidative DNA Damage in UV-Exposed Human Cell Lines.” Toxicological Sciences, vol. 114, no. 2, 13 Jan. 2010, pp. 272–284, 10.1093/toxsci/kfq005. Accessed 4 July 2021.

Jang, Gun Hyuk, et al. “Sequential Assessment via Daphnia and Zebrafish for Systematic Toxicity Screening of Heterogeneous Substances.” Environmental Pollution, vol. 216, Sept. 2016, pp. 292–303, 10.1016/j.envpol.2016.06.001. Accessed 5 Dec. 2020.

“Octinoxate – Haereticus.” Haereticus, haereticus-lab.org/octinoxate/.

“Octinoxate in Cosmetics.” Healthline, 7 Apr. 2021, http://www.healthline.com/health/octinoxate#the-bottom-line. Accessed 7 Sept. 2021.

Ozáez, Irene, et al. “Ultraviolet Filters Differentially Impact the Expression of Key Endocrine and Stress Genes in Embryos and Larvae of Chironomus Riparius.” Science of the Total Environment, vol. 557-558, July 2016, pp. 240–247, 10.1016/j.scitotenv.2016.03.078. Accessed 27 Apr. 2021.

“What Is Octinoxate and Is It Safe in Sunscreen?” Goddess Garden, 14 May 2017, http://www.goddessgarden.com/what-is-octinoxate-and-is-it-safe-in-sunscreen/. Accessed 7 Sept. 2021.

Zucchi, Sara, et al. “Global Gene Expression Profile Induced by the UV-Filter 2-Ethyl-Hexyl-4-Trimethoxycinnamate (EHMC) in Zebrafish (Danio Rerio).” Environmental Pollution, vol. 159, no. 10, Oct. 2011, pp. 3086–3096, 10.1016/j.envpol.2011.04.013. Accessed 7 Sept. 2021.