SUNSCREENS WITH BROAD-SPECTRUM ABSORPTION DECREASE THE TRANS TO CIS PHOTOISOMERIZATION OF UROCANIC ACID IN THE HUMAN STRATUM-CORNEUM AFTER MULTIPLE UV-LIGHT EXPOSURES
Pm. Krien et D. Moyal, SUNSCREENS WITH BROAD-SPECTRUM ABSORPTION DECREASE THE TRANS TO CIS PHOTOISOMERIZATION OF UROCANIC ACID IN THE HUMAN STRATUM-CORNEUM AFTER MULTIPLE UV-LIGHT EXPOSURES, Photochemistry and photobiology, 60(3), 1994, pp. 280-287
The trans to cis photoisomerization of urocanic acid (UCA) in skin is
considered to play an important role in the mechanism of immunosuppres
sion. We have investigated the effects of skin type and various sunscr
eens with low sun protection factor (SPF) on the UV-induced cis-UCA fo
rmation 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 decr
eases with increasing SPF and only broad-spectrum, highly protective s
unscreens 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 similar to 10(-17) m(2)/s, and that its
elimination from the stratum corneum is mainly due to desquamation.