Especially in summer, shelves in supermarkets and drugstores are full of a variety of sunscreen products across all price ranges. And a good sun or UV protection is indispensable in particular for people who are more or less light-skinned, because UV rays can lead to health problems.  In the worst case scenarios, the consequences could mean life-threatening forms of cancer, whereas premature ageing of the skin is unpleasant but relatively harmless.

As a protection against these UV rays, sunscreen products use chemical UV filters which in most cases have one thing in common: they are often harmful to a person’s health and the environment because they are based on minerals such as titanium dioxide or they contain microplastics. “The toxicity of some of these organic filters for marine life is problematic. Unfortunately, practically all organic filters – along with the vast majority of all other organic chemicals that abound – are being produced from petroleum,”  scientists state.

An international research team headed by Prof. Dr. med. Till Opatz from the Institute of Organic Chemistry at Johannes Gutenberg University Mainz (JGU) and Prof. Dr. Med. Charles de Koning from the University of the Witwatersrand in Johannesburg have now succeeded in using cashew nut shell liquid (CNSL, alternatively known as cashew nut oil or cashew shell oil) instead of petroleum in organic synthesis. This liquid is produced in large quantities during the production process of the nuts and cannot be used as a food or animal feed. As a result, there is no competition between its use as a chemical raw material and production of foodstuffs.

Scientists from Mainz and Johannesburg with a sample of the cashew nut shell liquid based starter material for the UV absorber. ©: Opatz Lab

Product of little commercial value but high technological potential

“With current concerns over the use of fossil resources for chemical synthesis of functional molecules and the effect that current UV absorbers in sunscreens have on the ecosystem, we define the xylochemical synthesis of different classes from aromatic UV absorbers utilizing cashew nut shell liquid – as a non‐edible bio‐renewable carbon source,” the researchers emphasize in their study, which was published in the European Journal of Organic Chemistry.

CNSL is a product of “little commercial value but with high technological potential,” Opatz and his team explain. Because the liquid contains readily extractable phenolic components as well as biological substances, which include, among others, antimicrobial, anti-inflammatory, antioxidant, insecticidal and even antitumoral substances. The phenols that are also contained in the cashew shell would be suitable as raw materials for chemical syntheses too.

According to the scientists, further research has yet to confirm whether the precisely-defined chemical UV absorbers obtained in this way are also suitable for sunscreens, how they are tolerated by the skin, and what effects they have on various organisms. “This research, however, is beyond the scope of the current project funded by the German Federal Ministry of Education and Research (BMBF) and the South African NRF partner organization. Further research will require collaboration with industry.”

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