PHOTOPROTECTION IN VITILIGO AND NORMAL SKIN - A QUANTITATIVE ASSESSMENT OF THE ROLE OF STRATUM-CORNEUM, VIABLE EPIDERMIS AND PIGMENTATION

Pigmentation, stratum corneum and viable epidermis are considered to b e the main factors protecting against ultraviolet radiation. We quanti tatively investigated the degree of photoprotection provided by these structures in vitiligo and adjacent normally pigmented skin, In 14 pat ients 61 MED tests were performed in vitiligo and adjacent normally pi gmented skin using a solar simulator. The thickness of stratum corneum and viable epidermis was determined from frozen skin sections, and pi gmentation was calculated by measuring skin reflectance at 555 mn and 660 mm, To analyse photoprotection, the UV dose necessary to evoke ery thema was regressed against the thickness of stratum corneum and viabl e epidermis, pigmentation and the erythema grade in the MED test, By a nalysing regression coefficients we found that stratum corneum was the main photoprotective factor not only in vitiligo but also in normally pigmented skin, The effect of pigmentation in normal skin was slightl y less prominent, Stratum corneum was thicker in vitiligo than in norm ally pigmented skin, However, the photoprotection due to stratum corne um was similar in both groups because significantly less photoprotecti on was achieved per thickness unit of stratum corneum in vitiligo than in normal skin. Neither in vitiligo nor in;normally pigmented skin di d the photoprotection depend on viable epidermis, Our data quantitativ ely document the importance of stratum corneum and pigmentation. Hyper keratosis in vitiligo offers just as efficient photoprotection as does the normal stratum corneum in pigmented skin.