Quantitative and qualitative effects of chemical peeling on photo-aged skin: An experimental study

Chemical peel reverses the visible stigmata of photo aping in human skin. T he qualitative and, in particular, the quantitative changes in the dermis t hat effect this transformation are unclear. This study used a recognized ph oto-aged animal model, the Skh:HR-1 hairless mouse, to quantify and qualify the changes that occurred in collagen and glycosaminoglycan content after chemical peel. One hundred Skh:HR-1 hairless mice were photo-aged by use of chronic ultraviolet B irradiation for 14 weeks. After irradiation the anim als were randomly distributed into five groups of 20 mice each: group 1, co ntrol; group 2, 50% glycolic acid peel; group 3, 30% trichloroacetic acid p eel; group 4, 50% trichloroacetic acid peel; group 5, phenol peel (Baker-Go rdon formula). The respective peeling agent was applied to the dorsal skin of each animal while it was fully anesthetized. Punch biopsies were taken a t several times after peel for histological and biochemical analysis. Glyco saminoglycan content was assessed at 14, 28, and 60 days using a colorimetr ic assay. Collagen content per unit volume increased initially 3 days after the procedure in all chemical peel groups, declining on day 7, and peaking again on day 28. Significant elevations (p < 0.84) were seen in the 30% tr ichloroacetic acid, 50% trichloroacetic acid, and phenol peels on days 3 an d 28 in comparison with controls. This increase in collagen content was not maintained and returned to control values bu 60 days. Glycosaminoglycan co ntent per unit volume was elevated initially after peel with significant el evation (p < 0.02) in the 50% trichloroacetic acid and phenol groups on day s 14 and 28. This increase in glycosaminoglycan content was not maintained beyond 28 days and declined to control Values by day 60 in all groups. Hist ological examination demonstrated an increase in dermal thickness in the 50 % trichloroacetic acid and phenol groups in comparison with controls by day 60. Under polarized Light all chemical peel groups at day 60 demonstrated a reorganization of collagen in the reticular and papillary dermis. The ela stotic masses that are pathognomonic of photo aging were present in the con trol group but were absent in the peer groups and demonstrated a reorganiza tion of the elastic fibers in the dermis. This effect was deeper in the der mis in the deeper peel groups (50% trichloroacetic acid and phenol peel). T he beneficial effects of chemical peel were due to a combination of two fin dings; a reorganization in dermal structural elements and an increase in de rmal volume. These effects were more pronounced in the deeper peer groups.