Combining UV protection with radiative cooling, scientists have developed a sunscreen that reflects both sunlight and heat.
The secret lies in specially sized titanium dioxide nanoparticles, ensuring cooler skin and reliable sun protection.
Combining UV Protection and Cooling
Wearing sunscreen is essential to protect your skin from harmful UV rays, but it doesn’t help with staying cool. Now, researchers have developed a groundbreaking formula, detailed in the scientific journal ACS Nano Letters, that offers both UV protection and heat relief by leveraging radiative cooling.
This innovative sunscreen prototype can keep skin up to 11°F (6°C) cooler than bare skin and about 6°F (3°C) cooler than current sunscreens.
Radiative Cooling: A Dual Purpose Solution
Radiative cooling works by reflecting or radiating heat away from a surface, effectively cooling what lies beneath. This principle has already been used to design cooling fabrics and energy-efficient coatings for buildings.
A key ingredient in some of these technologies is titanium dioxide (TiO2), a whitish compound known for its ability to reflect heat. While TiO2 is commonly used in mineral sunscreens to block UV rays, its standard particle size isn’t effective for radiative cooling. To solve this, Rufan Zhang and their team fine-tuned the size of TiO2 nanoparticles, creating a sunscreen that combines effective UV protection with the added benefit of cooling the skin.
Innovating with Titanium Dioxide Nanoparticles
The team created their sunblock by combining six ingredients: TiO2 nanoparticles, water, ethanol, moisturizing cream, pigments, and a common silicone polymer used in cosmetics called polydimethylsiloxane. By carefully adjusting the sizes of the TiO2 nanoparticles, they produced a material that reflects both UV light and solar heat, imparting the cooling ability.
The new formulation demonstrated an SPF of about 50, water resistance, and continued efficacy after 12 hours of simulated sunlight exposure with a xenon lamp. Additionally, when applied to both animal and human skin, the product didn’t cause irritation.
Real-World Tests and Commercial Potential
In tests on people in a hot and humid outdoor environment, the new radiative cooling sunscreen was found to keep the participants’ skin up to 10.8 F (6.0 C) cooler than bare skin, and up to 11.0 F (6.1 C) cooler than commercially available sunscreens. The formulation is inexpensive, costing only $0.92 for 10 grams of the mixture — on par with sunblocks already on the market. The researchers say their sunscreen prototype exhibits promising commercial potential, especially as temperatures in the summer continue to rise.
Reference: “High-Performance Radiative Cooling Sunscreen” by Jiaqi Xu, Xueke Wu, Yunrui Li, Siming Zhao, Fan Lan, Aike Xi, Ya Huang, Yilin Ding and Rufan Zhang, 15 November 2024, Nano Letters.
DOI: 10.1021/acs.nanolett.4c04969
The authors acknowledge funding from the National Key Research Program, the National Natural Science Foundation of China and the Tsinghua-Toyota Joint Research Fund.
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