Effects of glycolic acid on light-induced skin pigmentation in Asian and Caucasian subjects

Background: Topical use of cx-hydroxy acid (AHA) may increase skin photosen sitivity, as demonstrated by increased numbers of sunburst cells. However, effects of AHA on tanning have not been studied. Objective: Our purpose was to study whether short-term use of glycolic acid hastens resolution of pre-existing light-induced pigmentation and whether the skin becomes tan more easily in Asian and Caucasian subjects after such treatment. Methods: Six Asian and six Caucasian volunteers received separate irradiati ons of UVB and Wh to both sides of the lower back. In a double-blind fashio n, patients then applied a 10% glycolic acid gel, pH 3.52, to one side of t he back, including the irradiated area, and the contralateral extensor fore arms once daily for 7 days and then twice daily for 2 weeks. A placebo gel, pH 5.75, was applied to the opposite sides. The subjects returned for meas urement of residual tanning with a colorimeter and received additional irra diation to forearms and a second site on the back. Resulting pigmentation was measured immediately after irradiation, at 2 hou rs, and at 1 week. Results: Increased UVB-induced skin tanning occurred on the forearm and the lower back in both races in areas pretreated with glyco lic acid. UVA also caused increased tanning, but only on the extensor forea rms in Asian subjects. Treatment with glycolic acid for 3 weeks had no effe ct on pre-existing light-induced pigmentation. Conclusion: Shore-term topical treatment of glycolic acid caused an increas e in UVB tanning as well as in UVA tanning in some subjects, even in the ab sence of overt irritation. The inclusion of UVB, and even UVA, sunscreen in AHA products may be warranted.