ROLE OF SUN EXPOSURE ON NEVUS - 1ST STUDY IN AGE-SEX PHENOTYPE-CONTROLLED POPULATIONS

Background: These studies were designed to assess the influence of sun exposure on nevi in white people. To eliminate the confounding effect of age, sex, and phenotype, two parallel studies were conducted on pe ople of the same age (17 to 24 years; median, 20 years old), sex (male ), and phenotype: one in people with ''red'' phenotype (red or red-blo nd hair, white complexion on the inner part of the arm, and inability to tan) and one in people with ''dark'' phenotype (brown or black hair , dark complexion on the inner part of the arm, absence of freckles, a nd easy tanning without burning). Results: In both groups, comparison of nevus counts on the inner and outer side of the upper extremities a nd comparison of mean density of nevi (number per square meter) in alw ays-exposed and never-exposed skin show that the number of nevi is hig her in sun-exposed areas. The density of large and atypical nevi was m aximal on intermittently sun-exposed skin while the density of small n evi was maximal on always-exposed skin. The number of large nevi on in termittently exposed skin correlated with cumulative intensive exposur e during beach recreation in the red phenotype group. The number of la rge nevi was significantly higher in red phenotypes who repeatedly exp erienced severe sunburns in their first 20 years of life. Conclusions: The number of nevi at the end of the second decade is influenced by c umulative sun exposure from birth. ''Traumatizing'' sun exposure, whic h is more frequent in the red phenotype than in the dark phenotype, ha s an influence on the number of large nevi and is therefore likely to make small nevi grow.