Cosmetics That Adapt One to Harsh Environments: Utilizing Heat to Enhance the UV Protective Effect

Due to continuous global warming and changes in the atmosphere of the Earth, we are facing harsher environments such as high temperatures and exposure to excessive UV radiation. The increase of UV damage is known to adversely affect the human body, necessitating improved protection methods against it. Among available resources on the Earth's surface, we focused on temperature, which is continually increasing, closely synchronized to UV radiation on Earth. We developed a technology that considerably improves UV protection by exposure to high temperature by combining UV absorbers with polyoxyethylene/polyoxypropylene-9/2 dimethyl ether (PPDE). To elucidate the mechanism, in silico experiments were performed using ethylhexyl methoxycinnamate (EHMC), a model UV absorber with particularly high UV protective effect at elevated temperatures. The results indicated that a part of EHMC molecules form a dimer structure at 20℃, imparting low UV protection, and the molecule dissociates into a monomer structure at 40℃, providing a high UV protective effect. The PPDE-EHMC combination reduces the molecular motion at 20℃, allowing maintenance of the monomer structure, and prolongs the UV protective effect, which result matches in vitro results. Through this research, it was found that the UV absorbers used for many years are in the dimeric state, which has low protection effect at room temperature, but are converted to monomers under high temperature, resulting in higher UV protection. Importantly, we also discovered that PPDE acts as a novel factor which contributes to providing a higher UV protection, and its addition is key to maintaining that high protective state of UV absorbers even when returned to room temperature. This result provides an effective strategy for improved skin protection from UV radiation under the scorching sun and contributes to maximizing the UV protective effect with this newly developed sunscreen.