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 (B asque Country, Spain). Measurements were taken at the upper inner arm and f orehead by means of an EEL DS29 Digital Unigalvo reflectance spectrophotome ter fitted with filters 601, 605, and 609, The reflectance data were intern ally standardized according to sex and age of the individuals, and the anal ysis of the degree of similarity between siblings was based on the calculat ion of intraclass correlation coefficients. All 3 filters gave fairly high and statistically significant correlations regarding forehead skin color (b etween 0.28 and 0.45) for all types of siblings under consideration. Howeve r, with respect to filter 609 the arm reflectance values did not reveal cor relation either between brothers (0.01) or between siblings (0.02), even th ough it did reveal correlation between sisters (0.29). When other filters o r type of sibling were considered (also for arm), all coefficients happened to be statistically significant and relatively high (0.35-0.43). This stud y confirms that the degree of sibling resemblance with regard to skin pigme ntation is influenced by growth factors and that the upper inner arm and th e forehead skin patterns change with age in the sense that, during and espe cially after puberty, the coefficients of correlation are higher for arm re flectance than for forehead reflectance; the forehead is a site that is mor e influenced by environment.