Conservation and Biodiversity

This nutty idea could be key to an ecofriendly tan

Without sunscreen, we burn. But with it, we might burn ecosystems. Chemicals in commercial sunscreens are petroleum based, disruptive to biodiversity and not biodegradable. If you’re just looking for a tan this summer, what’s a beach bum to do?

This guilt-ridden dilemma is what a team of chemists set out to address with a potential plant-based sunscreen. The research, published this month in the European Journal of Organic Chemistry, highlights a potentially ecofriendly way of making sunscreen: by using cashew nut shells.

“Cashew nut shells are waste,” said Charles de Koning, professor at University of the Witwatersrand in South Africa and principle author of the paper, in an email. “We have extracted compounds from [cashew nut shells] to be used as ‘building blocks’ to make what we call ‘functional materials.’” One functional material would be a more environmentally friendly sunscreen.

Finding an ecofriendly sunscreen is important for our health as well as the planet’s. Many compounds found in sunscreen are petroleum based, making them a contributor to global warming. And then there’s the negative impact on biodiversity in marine life.

A recent study suggested that oxybenzone, a common ingredient of sunscreens, “poses a hazard to coral reef conservation and threatens the resiliency of coral reefs to climate change.” The study showed that this common chemical, found in more than 3,500 skincare products, affected developing coral in several ways: increasing susceptibility to bleaching, damaging DNA and causing deformities in baby coral.

According to the National Oceanic and Atmospheric Administration, chemicals in sunscreen can also impair growth and photosynthesis of green algae, deform mussels and sea urchins and decrease fertility in fish.

A nutty solution

Cashew nut shells “contain building blocks that can be converted into UV absorbers that are aromatic and have a hydrogen-bonded moiety,” explained de Koning, making them good absorbers of ultraviolet radiation, the rays emitted from the sun.

Additionally, cashew nut shells are common waste products in places like Tanzania, so finding a productive use for them would be a net benefit. And since nut shells are waste, potentially turning them into sunscreen doesn’t take away from food sources, either.

To convert these hard nut shells into something useful like sunscreen, the team of researchers used a process called xylochemistry, or wood- and plant-based chemistry, to extract aromatic compounds from the shells. After extracting these compounds — specifically anacardic acid and cardanol — the team used chemical reactions to convert the compounds into UV absorbers.

The researchers showed that some compounds from plant-based products effectively absorb UV rays, even better than some sunscreens currently on the market. Now the team is exploring ways to test the toxicity of UV absorbers, as well as ways to invent better chemical reactions to synthesize UV absorbers.

Coral reefs play a major role in industries like eco-tourism and fisheries and are home to more than a quarter of marine life. But climate change, chemicals and pollutants threaten the resiliency and biodiversity of coral reefs. Innovations like nut-shell sunscreens could help curb these threats and put us on the path of a more sustainable future.

Learn more about coral reefs at Earth Day Network and remember to buy and use sunscreens that are free of oxybenzone.