Skin Surface Topography and Texture Analysis of Sun-Exposed Body Sites in View of Sunscreen Application.

BACKGROUND/AIMS: To determine the roughness of the surface of human skin at highly sun-exposed anatomical sites in a wide age range in order to derive consequences for sunscreen application. METHODS: The forehead, cheek, nose, shoulder, and dorsal hand of 4 age groups (0-9, 20-39, 40-59, and >60 years) were investigated by replica formation, and areal topography was determined by confocal chromatic imaging. The arithmetic mean height as a roughness parameter and the void volume of the surface profile were calculated. RESULTS: Age and site had a significant effect on roughness. Both the dorsal hand and nose exhibited the greatest roughness over the age of 40, and the forehead of the youngest age group exhibited the smallest roughness. Differentiation between sites progressed with age, whereas roughness increased significantly with age for the dorsal hand and nose but not for the other sites. The void volume was smaller than the volume corresponding to the typically recommended amount of sunscreen application except for the cases of largest roughness. CONCLUSIONS: Different site-age combinations show significant variation of skin surface roughness. The application of sunscreen may in some instances need to be adjusted to take into account the increased roughness of highly sun-exposed anatomical sites.

Porcine ear skin as a biological substrate for in vitro testing of sunscreen performance.

PURPOSE: The purpose of the study was to examine the use of skin from porcine ears as a biological substrate for in vitro testing of sunscreens in order to overcome the shortcomings of the presently used polymethylmethacrylate (PMMA) plates that generally fail to yield a satisfactory correlation between sun protection factors (SPF) in vitro and in vivo. PROCEDURES: Trypsin-separated stratum corneum and heat-separated epidermis provided UV-transparent substrates that were laid on quartz or on PMMA plates. These were used to determine surface roughness by chromatic confocal imaging and to measure SPF in vitro of 2 sunscreens by diffuse transmission spectroscopy. RESULTS: The recovered skin layers showed a lower roughness than full-thickness skin but yielded SPF in vitro values that more accurately reflected the SPF determined in vivo by a validated procedure than PMMA plates, although the latter had in part roughness values identical to those of intact skin. Combination of skin tissue with a high roughness PMMA plate also provided accurate SPF in vitro. CONCLUSIONS: Besides roughness, the improved affinity of the sunscreen to the skin substrate compared to PMMA plates may explain the better in vitro prediction of SPF achieved with the use of a biological substrate.