Evolution of melanocytic nevi on the faces and necks of adolescents: a 4 y longitudinal study.

All melanocytic nevi on the faces and necks of a cohort of students, initially aged 12-14 y, were mapped and photographed annually for 4 y. The features of each nevus were charted yearly noting changes in size and profile, and the appearance or disappearance of any nevi on a student's face and neck was recorded. Nevi were classified by size (small, < 2 mm; medium, 2-5 mm; large, > 5 mm), and by profile (flat, raised). Data from 20 adolescents selected randomly from the cohort for detailed analysis showed males had about twice as many nevi as females, but there was little difference between sexes in their patterns of nevus development. Approximately half the nevi were small in all years; under 5% were large. Over the 4 y of follow-up the proportion of flat nevi dropped from 70% to 57%, whereas nevus numbers increased by 47% in year 1, with smaller increases in older students. Most new or disappearing nevi were small and flat, although both incident and disappearing nevi could be larger and/or raised. Of the existing nevi that altered in the follow-up period, the tendency was towards an increase in size among raised but not among flat nevi; a lowering of profile among small nevi; and a raising of profile among larger nevi; but there were many exceptions to this pattern. Among several host factors examined, inability to tan after sun exposure was found to be significantly negatively associated with the propensity of nevi to change size over the study period. Overall our findings indicate that, contrary to conventional belief, there is a measurable turnover among melanocytic nevi even in early life.