Double Defense: New Sunscreen Protects Your Skin While Helping You Stay Cool

Extreme summer temperatures are becoming more common as our planet warms, posing both immediate safety threats and potential long-term health complications. Existing sunscreen products offer protection by absorbing or reflecting ultraviolet (UV) radiation—blocking the UVA that causes sunburn as well as the UVB that penetrates deeper, causing skin aging and cancer.¹ That said, there are some controversies around sunscreens and the chemicals in them, such as oxybenzone, which is both environmentally toxic² and disruptive to certain hormones.³ It’s also interesting to note that sunscreen is less effective than protective clothing or sun avoidance—and the so-called sunscreen paradox has shown that use of these products is actually associated with twice the risk of developing skin cancer,⁴ perhaps due to improper application or complete lack of reapplication during extended periods of sun exposure.

But UV accounts for less than 5% of solar radiation, so even when wearing sunscreen, we still absorb visible and near-infrared solar radiation. This can cause rapid skin heating, leading to risk of potentially deadly heat exhaustion and heat stroke.⁵ Hot temperatures also contribute to deaths from heart attacks, strokes, and other forms of cardiovascular disease. According to the Environmental Protection Agency, heat-related deaths in the U.S. reached new highs in 2021 and 2022—two of the hottest years on record with several significant heat waves.⁵ To maintain comfort in outdoor environments, there is an increasing need for new sunscreen formulas that can both protect our skin while simultaneously regulating our body surface temperature.

One technology that has attracted attention is radiative cooling—a zero-energy method that transfers radiative heat using high solar reflectivity. Some sunscreens already include ingredients such as titanium dioxide to achieve some reflective properties, but existing formulations have yet to produce a cooling effect. To address this, researchers at Tsinghua University began experimenting with various sizes of titanium dioxide nanoparticles to develop a sunscreen that could regulate UV, visible, and both near- and mid-infrared wavebands over a range of 0.2–25 μm.

The results, published in Nano Letters, demonstrated excellent UV shielding alongside high solar reflectivity in excess of 90%, as well as high emissivity—which ultimately was able to decrease skin temperature by up to 6.1°C more than commercial sunscreens and 6.0°C more than bare skin in a variety of outdoor summer scenarios. Additionally, the sunscreen showed good UV stability, water resistance, and biocompatibility, suggesting this could be a promising approach for new commercial products.

Further Explorations: Radiative Cooling

Radiative cooling could also be useful to develop fabrics for sun and heat protection. As we recently highlighted in this post, a 2024 study in ACS Applied Materials & Interfaces reports on incorporating zinc oxide and polyethylene into polymers, which are then electrospun into nanofabrics to reflect sunlight and transmit mid-infrared radiation.⁷ Another group has developed a hierarchically nanofibrous (HNF) textile with three layers: a side that cools, a side that heats, and a middle layer that insulates.⁸ Tests demonstrated that the fabric can make you feel cooler by 7.2°C in hot weather and warmer by 12.2°C in cold weather compared to regular cotton. Plus, its breathability and self-cleaning properties make it an ideal candidate for extreme temperatures.

On a larger scale, the passive nature of radiative cooling has the potential to lower building temperatures and reduce global warming by reducing CO₂ emissions from traditional cooling methods⁹—an important consideration since technologies such as air conditioning require a large energy input, themselves becoming part of the problem. As temperatures and deadly heatwaves continue to rise, these radiative cooling technologies offer a way for us to further protect ourselves in—and from—our changing environment.

Browse even more articles on radiative cooling in ACS journals:

Special Issue: Optical Materials for Radiative Cooling
ACS Applied Optical Materials

Radiative Cooling Face Mask
Sudip Kumar Pal, Dong Yun Choi, and Gunwoo Kim*
DOI: 10.1021/acsapm.3c00541

Superhydrophobic Designs for Durable Radiative Cooling
Hongmei Zhong, Shouwei Gao, and Zuankai Wang*
DOI: 10.1021/acs.langmuir.3c02946

Advanced Bioinspired Personal Thermoregulation Textiles for Outdoor Radiative Cooling
K. M. Faridul Hasan, Jianheng Chen, Siru Chen, Kaixin Lin, Man Yi Wong, Lin Liang, Yihao Zhu, Aiqiang Pan, Yitbarek Firew Minale, Tsz Chung Ho, Carol S. K. Lin, and Chi Yan Tso*
DOI: 10.1021/acsami.4c18812

Switchable and Tunable Radiative Cooling: Mechanisms, Applications, and Perspectives
Xuzhe Zhao, Jiachen Li, Kaichen Dong*, and Junqiao Wu*
DOI: 10.1021/acsnano.4c05929

References

1. Mancebo, S. E. et al. Sunscreens: A Review of Health Benefits, Regulations, and Controversies. Dematologic Clinics. 2014, 32 (3), 427–438.
2. Li, S. et al. Proteomics and Lysine Acetylation Modification Reveal the Responses of Pakchoi (Brassica rapa L. ssp. chinensis) to Oxybenzone Stress. J. Agric. Food Chem. 2023, 71, 22, 8332–8344.
3. Li, Z.-M. et al. Comprehensive Survey of 14 Benzophenone UV Filters in Sunscreen Products Marketed in the United States: Implications for Human Exposure. Environ. Sci. Technol. 2022, 56, 17, 12473–12482.
4. Jeremian, R. et al. Gene–Environment Analyses in a UK Biobank Skin Cancer Cohort Identifies Important SNPs in DNA Repair Genes That May Help Prognosticate Disease Risk. Cancer Epidemiol Biomarkers Prev. 2023, 32 (11), 1599–1607.
5. Climate Change Indicators: Heat-Related Deaths. United States Environmental Protection Agency, June 2024.
6. Xu, J. et al. High-Performance Radiative Cooling Sunscreen. Nano Lett. 2024, 24, 47, 15178–15185.
7. Iqbal, M. I. et al. Radiative Cooling Nanofabric for Personal Thermal Management. ACS Appl. Mater. Interfaces 2022, 14, 20, 23577–23587.
8. Gu, B. et al. A Hierarchically Nanofibrous Self-Cleaning Textile for Efficient Personal Thermal Management in Severe Hot and Cold Environments. ACS Nano 2023, 17, 18, 18308–18317.
9. Li, X. et al. Ultrawhite BaSO₄ Paints and Films for Remarkable Daytime Subambient Radiative Cooling. ACS Appl. Mater. Interfaces 2021, 13, 18, 21733–21739.