Sunscreens with broad-spectrum absorption decrease the trans to cis photoisomerization of urocanic acid in the human stratum corneum after multiple UV light exposures.
The trans to cis photoisomerization of urocanic acid (UCA) in skin is considered to play an important role in the mechanism of immunosuppression. We have investigated the effects of skin type and various sunscreens with low sun protection factor (SPF) on the UV-induced cis-UCA formation in human skin after exposure to artificial UV light. The rate of cis-UCA formation depends little on the skin type and is reduced by topical application of sunscreens. The rate of cis-UCA formation decreases with increasing SPF and only broad-spectrum, highly protective sunscreens offer protection against the UV-induced formation of cis-UCA, which accumulates in the stratum corneum after multiple UV exposures. A theoretical approach to estimate the distribution of cis-UCA after irradiation indicates that this compound may diffuse into the deeper layers of the epidermis with D approximately 10(-17) m2/s, and that its elimination from the stratum corneum is mainly due to desquamation.
L'Oreal, Charles Zviak Research Center, Clichy, France.
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D001892:Camphanes; D002164:Camphor / Q000031:analogs & derivatives* / Q000494:pharmacology; D002934:Cinnamates / Q000494:pharmacology*; D006801:Humans; D007536:Isomerism; D007700:Kinetics; D008214:Lymphocytes / Q000187:drug effects* / Q000528:radiation effects; D008698:Mesylates / Q000494:pharmacology*; D008962:Models, Theoretical; D010777:Photochemistry; D012867:Skin / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D013451:Sulfonic Acids; D013473:Sunscreening Agents / Q000494:pharmacology*; D014466:Ultraviolet Rays; D014560:Urocanic Acid / Q000378:metabolism / Q000528:radiation effects*
D001892:Camphanes; D002934:Cinnamates; D008698:Mesylates; D013451:Sulfonic Acids; D013473:Sunscreening Agents; C075352:terephthalylidene dicamphor sulfonic acid; C118580:octylmethoxycinnamate; D002164:Camphor; D014560:Urocanic Acid