Sibling correlations of skin pigmentation during growth

The present study is focused on the analysis of skin color correlations in a sample of 1039 siblings aged 4 to 20 years from the province of Biscay (Basque Country, Spain). Measurements were taken at the upper inner arm and forehead by means of an EEL DS29 Digital Unigalvo reflectance spectrophotometer fitted with filters 601, 605, and 609. The reflectance data were internally standardized according to sex and age of the individuals, and the analysis of the degree of similarity between siblings was based on the calculation of intraclass correlation coefficients. All 3 filters gave fairly high and statistically significant correlations regarding forehead skin color (between 0.28 and 0.45) for all types of siblings under consideration. However, with respect to filter 609 the arm reflectance values did not reveal correlation either between brothers (0.01) or between siblings (0.02), even though it did reveal correlation between sisters (0.29). When other filters or type of sibling were considered (also for arm), all coefficients happened to be statistically significant and relatively high (0.35-0.43). This study confirms that the degree of sibling resemblance with regard to skin pigmentation is influenced by growth factors and that the upper inner arm and the forehead skin patterns change with age in the sense that, during and especially after puberty, the coefficients of correlation are higher for arm reflectance than for forehead reflectance; the forehead is a site that is more influenced by environment.