Although sunscreens help protect our skin from the sun's harmful UV rays, they are not designed to keep skin cool. However, an experimental new sunscreen does just that while maintaining an SPF of around 50.
Commonly used mineral-based sunscreens typically contain tiny particles of titanium dioxide and/or zinc oxide.
These nanoparticles reflect much of the ultraviolet light present in sunlight, preventing it from reaching and damaging the underlying skin. However, the particles are too small to reflect the sun's infrared light, which transmits heat energy. Therefore, people who wear sunscreen can still get uncomfortably or even dangerously hot.
Assoc. Prof. Rufan Zhang and colleagues at China's Tsinghua University recently set out to change this by carefully optimizing the size of titanium dioxide nanoparticles. Ultimately, the scientists were able to create particles that still reflected UV light Also reflect a significant amount of infrared light.
However, the nanoparticles alone couldn't accomplish this task, so they were mixed with deionized water, ethanol, Nivea moisturizer, skin-colored iron oxide pigments, and a silicone polymer called polydimethylsiloxane (which is often used in cosmetics).
Adapted from Nano Letters 2024, DOI: 10.1021/acs.nanolett.4c04969
When the resulting sunscreen was tested on human volunteers in a hot and sunny outdoor environment, it was found to increase their skin temperature by up to 6.1ºC (11ºF) compared to commercial sunscreens and by 6.0ºC compared to commercial sunscreens (10.8ºF) reduced to no sunscreen.
In addition, it showed a sun protection factor of around 50 and remained effective – and water-resistant – even after 12 hours of simulated sunlight exposure from a xenon lamp. Additionally, tests conducted on both mice and humans showed that it did not irritate the skin.
The scientists estimate that producing the heat-reflecting sunscreen on a commercial scale would cost about 92 cents per 10 grams (0.4 ounces), reportedly putting it “on par” with existing commercial sunscreens.
An article about the research was recently published in the journal Nano letters.
Source: American Chemical Society