EPIDERMAL THICKNESS, SKIN PIGMENTATION AND CONSTITUTIVE PHOTOSENSITIVITY

The important factors for UV sensitivity in humans are considered to b e the skin pigmentation and the epidermal thickness. In this study on 73 Caucasians (age 20-85 years), we investigated in UV unexposed butto ck skin the relationship between the UV sensitivity and constitutive s kin pigmentation and thickness of the stratum corneum and the cellular part of the epidermis, in 34 normal people and in 39 skin cancer pati ents (20 patients with cutaneous malignant melanoma and 19 patients wi th basal cell carcinoma of the skin). Skin pigmentation was measured b y skin reflectance spectroscopy, and UV sensitivity by phototest with a solar simulator. Thicknesses of the stratum corneum and the cellular part of the epidermis were determined by light microscopic evaluation of skin biopsies from the phototest areas. We found that epidermal th ickness was independent of skin type and was not correlated to constit utive skin pigmentation. Thickness of the stratum corneum was statisti cally not different in normal persons and in skin cancer patients (P=0 .41) and was independent of gender (P=0.61) and age (P=0.56), while th ickness of the cellular epidermis decreased with age (P<0.01). Stratum corneum thickness was found to be of minor importance for the constit utive UV sensitivity (accounting for on average 11% of the total photo protection), which was mainly determined by the constitutive skin pigm entation (goodness-of-fit for correlation r=0.83). A theoretical model for the relationship of UV dose to induction of clinical erythema gra de and skin pigmentation and thickness of the stratum corneum was deve loped. Objective measurements of skin pigmentation in UV unexposed ski n by skin reflectance spectroscopy in Caucasians, normal people and pe ople with cutaneous malignant melanoma and basal cell carcinoma of the skin predicts the constitutive UV sensitivity with a high degree of p recision.