Beta-carotene does not act as an optical filter in skin

Abstract

Beta-carotene, when orally administered, only slightly increases the sunburn threshold in normal humans but effectively diminishes sunlight risk in patients suffering from erythropoietic protoporphyria. In addition, β-carotene has been shown to inhibit UV-induced carcinogenesis in mice when administered either orally or intraperitoneally. To examine the photoprotective properties of β-carotene, SKH-HR1 albino hairless mice received β-carotene supplemented diets for either two or four weeks. At the end of each treatment period the skins were visibly yellow. Whole skin and epidermis from each animal were studied by forward scattering transmission spectroscopy and compared with age-matched controls. While no major optical differences were seen in the whole skin or in the epidermis, the presence of β-carotene was optically demonstrated by weak but typical β-carotene absorption peaks in the epidermis following the two week feeding period. The peaks were also apparent in the four week group. However, the β-carotene peaks could not be resolved through full thickness skin. Despite the yellow appearance of the skin, the absorbance due to the carotene was insufficient to impart significant photoprotection. These results confirm previous theoretical arguments that oral β-carotene treatment does not attain a sufficient concentration in the skin to produce a typical sunscreen effect by absorption of radiation. When β-carotene is effective in the treatment of photosensitivity, it must produce its protectiveness through an alternative mechanism.