Topical beta-carotene protects against infra-red-light-induced free radicals

: The influence of stress factors on human skin induces the production of free radicals. Free radicals react immediately with antioxidants contained in the skin, giving rise to their depletion and with the surrounding molecules, resulting in their damage, disorganization and even destruction. High amounts of free radicals are produced in the upper skin layers, i.e. mainly in the epidermis, subsequent to sun irradiation. Irradiation of the skin in the infra‐red (IR) range of the spectra, applied at physiological doses, can produce free radicals. The magnitude of destruction of antioxidants, such as carotenoids, can serve as a marker of the extent of the stress factor, characterized by the quantity of produced free radicals. In this study, measurements on the degradation of cutaneous carotenoids following IR skin irradiation of 12 healthy volunteers (skin type II), with two IR sources (standard infrared radiator = SIR and water filter infrared = wIRA) were taken using resonance Raman spectroscopy. Topical application of the antioxidant beta‐carotene (2 mg/cm2) provided protection for the human skin when exposed to IR radiation. The magnitude of the degradation of dermal carotenoids after IR irradiation was significantly higher for SIR than for wIRA irradiation, for both non‐treated and cream‐treated skin areas. The amount of destroyed carotenoids after IR irradiation was higher in the case of pretreatment with beta‐carotene than for the untreated skin, indicating that the superficial part of antioxidants is most important for protecting against external stressors. The direct comparison of beta‐carotene content was significantly higher for the cream‐treated compared to untreated areas for all pairs: baseline, wIRA, after wIRA, baseline SIR and after SIR. Additionally, topically applied carotenoids as a single antioxidant component are less stable than the carotenoids in the skin incorporated by nutrition and accumulated in a mixture with different antioxidant substances. Resonance Raman spectroscopy can be used for the non‐invasive measurements of carotenoids, which can be rated as marker substances of redox processes.