Photodegradation of commercial insect repellents containing <scp>DEET</scp> and <scp>IR</scp> ‐3535 under ultraviolet light associated or not with chemical ultraviolet filters evaluated by Raman spectroscopy

Abstract The use of insect repellents in areas with high solar radiation exposure has increased significantly due to dengue and chikungunya epidemics in Brazil. However, limited research exists on the photostability of these substances under ultraviolet (UV) radiation. This study aimed to evaluate the photolability of two common insect repellents, N , N ‐diethyl‐3‐methylbenzamide (DEET) and ethyl 3‐[acetyl(butyl)amino]propanoate (IR‐3535), and commercial products containing these active ingredients, including combinations with selected chemical UV filters, under simulated UV radiation using Raman spectroscopy. Samples were exposed to a UV‐A + UV‐B light source (7.0 mW/cm 2 ) for 8 h, and Raman spectra were collected before and after irradiation. Pure DEET, IR‐3535, ethanol, isopropyl myristate, and the commercial product containing IR‐3535 exhibited no significant spectral changes following UV exposure. In contrast, DEET diluted in ethanol and the commercial product containing DEET exhibited significant changes, including a decrease in DEET peaks at 524, 690, 1003, and 1606 cm −1 and an increase in the ethanol peak at 884 cm −1 . When UV filters were added to the commercial products containing DEET and IR‐3535, no significant changes were observed in the peaks associated with DEET, IR‐3535, or ethanol. However, alterations were observed in the spectra of the UV filters, suggesting that the filters conferred photoprotection to the repellent molecules via a competitive photon absorption mechanism, but also exhibited photodegradation of their own molecules. These findings suggest that the commercial product containing DEET is photolabile under UV exposure and that the inclusion of chemical UV filters can restore photostability.