Background: Concerns about photosensitizing potential of alpha hydroxy acids have been expressed. A previous study, however, reported topical glycolic acid showing the opposite potential, that is, photoprotective. This study was designed to test the antiinflammatory and photoprotective capabilities of glycolic acid.
Objective: The effects of short-wave ultraviolet light (UVB) on skin treated with glycolic acid were evaluated in two different studies at two different locations.
Methods: In the first study the antiinflammatory potential of topical glycolic acid was tested on erythematous templates on the backs of human volunteers. Erythema was induced by exposure to three times the minimum erythema dose (MED) of UVB. Glycolic acid cream in an oil-in-water vehicle at 12% partially neutralized with ammonium hydroxide to a pH of 4.2 was applied to the template beginning 4 hours postirradiation four times a day. A second template on the same subject was used as a vehicle control. After 48 hours a marked reduction of erythema was noted when compared with the vehicle control site. In the second study, four test sites were exposed to UVB light in the following manner. Site 1 was a nontreated control site and was used to establish the MED for the subjects being tested; site 2 was also exposed to a MED series but was treated 24 hours postirradiation for 7 days with two glycolic acid-based products (cleanser and oil-free moisture lotion, both containing 8.0% glycolic acid at a pH of 3.25); site 3 was treated first with the two glycolic acid-based formulas for 3 weeks prior to being exposed to UVB light; and site 4 was treated as outlined in site 3, with the inclusion that the site was chemically peeled for 6 minutes (with a 50% glycolic solution at a pH of 2.75) 15 minutes prior to UVB exposure.
Results: When UVB-burned skin was treated with glycolic acid daily for 7 days (site 2), a 16% reduction in irritation was observed compared to nontreated skin (site 1), implying that skin healed sooner when treated with glycolic acid. When a comparison of nontreated skin was made to skin treated with glycolic acid for 3 weeks prior to UVB exposure (site 1 vs site 3), a sun protection factor (SPF) of 2.4 was achieved. When a comparison of skin treated for 3 weeks was made to skin treated for 3 weeks and chemically peeled (site 3 vs site 4) the data implied that the chemical peel reduced the SPF value of skin treated with glycolic by approximately 50%, however, an SPF trend of 1.7 was still obtained when compared with untreated skin. CONCLUSIONS. The studies demonstrated that topical glycolic acid provides a photoprotective effect to pretreated skin yielding an SPF of approximately 2.4. In addition, when glycolic acid is applied to irradiated skin, it accelerates resolution of erythema. The data obtained from both studies support the hypothesis that glycolic acids acts as an antioxidant.