A non-invasive computational method to determine the directionality of skin tension lines

The topography of human skin surface has cutaneous lines or skin tension lines whose orientation depends on factors like age, cosmetic use, environmental conditions, etc. Characterizing the orientation of these lines is of immense importance for the cosmetics industry, medical technology and applications like haptics. In this study we propose a simple method based on the ratio of the correlation length to the root mean square roughness along several profiles to characterize the directionality of these lines. This ratio is then normalized across all the profiles leading to a polar plot that varies between 0 and 1, with the major orientation appearing at a value of 1. Our results show that this non-invasive computational approach can be applied to skin roughness data or image intensities. As a practical application of the approach, we demonstrate its ability to capture changes in skin tension line orientation with age, using roughness data from the literature.