Skin color.

Quantitative measures of skin color were obtained by reflectance colorimetry with the use of the ChromaMeter 400 (CR-400; Konica Minolta). A measure of constitutive skin color was taken at the upper inner arm, midway between the axilla and medial epicondyle (17). Facultative skin color was measured at the posterior forearm, midway between the olecranon and the ulnar epicondyle, where skin color would consist of both the constitutive skin color and any tanning from sun exposure. Measurements were taken according to an established protocol (10, 15, 26), which further specified that measurements should avoid dense freckling or moles if present and should be repeated 3 times (4 measurements in total) at each site.

Skin color was measured along 2 axes: a lightness-darkness axis and a yellow-blue axis. Based on the mean of 4 measurements and these 2 variables, an individual typology angle (ITA) was calculated as an indicator of skin color (ITA = {[ArcTangent(L − 50/b)] × 180/π}), in which L represents degrees along the lightness-darkness axis, and b represents degrees along the yellow-blue axis) (27). Higher values of ITA correspond to lighter skin. The reliability of the ChromaMeter skin color readings has been verified in this study population previously (17). Tanning was calculated as the change in facultative skin color between pre-and post-summer time points.