Skin injury and protection in sexual assault: How skin elasticity varies by color and age in females

Background and Purpose: We have recently demonstrated decreased ano-genital injury prevalence in female victims of sexual assault with dark as compared to light skin. These findings raise questions about the association of the mechanical properties of skin, skin color, and age. The purpose of this study was to determine if skin elasticity varies by skin color and age. We defined skin elasticity as the skin's ability to change shape and return to normal position when stretched. Methods: Measures of skin elasticity included r2 (gross elasticity; the closer to 1 the more elastic the skin) and r7 (biological elasticity; ratio of elastic recovery to total deformation). We enrolled a convenience sample of 37 females (16 White; 8 Asian; 6 Latina; 3 Black; 4 Other) with a mean age of 24.92 years. Participants had measures of skin color (spectrophotometery: L*=lightness/darkness) and skin elasticity (cutometry; r2 and r7) completed on the external surface of the upper inner arm. Results: The correlation between r2 and r7 was large and significant (r=.80, p<.001). A multiple regression of r2 on L* values and age was significant overall (F(2,34)=4.47, p=.019), with 21% of the variation in skin elasticity accounted for by these two predictors. The relationship between r2 and L* values was significant and negative (b=-.00002, p=.027). Age was a stronger predictor of r2 than r7 values. Conclusions: Skin elasticity varies indirectly with age and skin color lightness. Females with dark skin may have a protective mechanism that helps explain lower ano-genital injury prevalence after sexual assault.