Prevalence of nevocytic nevi on lateral and medial aspects of arms

The numbers of clinically diagnosed, elevated nevocytic nevi (at least 2 mm in diameter) within 50 sq cm areas on the lateral and medial aspects of the arms of 1,000 subjects (age range 2 to 87 years) were compared. A total of 349 nevi was found on the lateral aspects and only 116 on the medial aspects of arms. Nevi were found on the lateral aspects of the arms in 23.4% (234) of the subjects and on the medial aspects in but 10.9% (109) of the subjects. These differences are highly significant in both men and women. Nevi were found in 30.2% (281) of the 930 whites but in only 9.1% (5) of the 55 blacks included in the study. Also, blacks did not show greater prevalence of nevi on the lateral as compared to the medial aspects of their arms. One explanation for the greater prevalence of nevi on the lateral over that on the medial aspects of the arms is that sunlight plays a role in the induction of acquired nevocytic nevi.