FUNCTIONAL-CHANGES IN HUMAN STRATUM-CORNEUM INDUCED BY TOPICAL GLYCOLIC ACID - COMPARISON WITH ALL-TRANS-RETINOIC ACID

The effects of topical glycolic acid and all-trans retinoic acid on st ratum corneum barrier function and hydration of human skin were invest igated in 6 healthy volunteers utilizing non-invasive techniques. In a ddititon, changes in stratum corneum turnover time induced by the subs tances were examined using the dansyl chloride fluorescence test. Twel ve percent glycolic acid in water and 0.1% retinoic acid in ethanol, r espectively, were applied for 60 min once daily, over a period of 2 we eks (5 consecutive days weekly) on dansyl chloride-labelled skin and o n untreated skin. During a 10-day application period, both glycolic ac id and retinoic acid similarly induced a significant increase in TEWL. However, after discontinuing treatment, TEWL in retinoic acid-exposed skin remained increased, Glycolic acid significantly reduced stratum corneum hydration from day 11 to day 18 (p<0.05), while retinoic acid induced skin dryness after 9 days of treatment, which persisted until day 18 (p<0.005). Whereas glycolic acid rapidly induced an intense ery thema implying a direct non-specific inflammatory response, the retino ic acid exposed skin gradually developed erythema. Retinoic acid cause d scaling to a greater extent than did glycolic acid, even after treat ment cessation. Both glycolic acid and retinoic acid significantly dec reased stratum corneum turnover time and stratum cor neum turnover tim e(50) (the time in days from labelling until approximately 50% of fluo rescence disappeared), compared with the vehicle controls. However, gl ycolic acid shortened stratum corneum turnover time (12.8 +/- 0.9 days ) as well as stratum corneum turnover time(50) (7.3 +/- 0.7 d) signifi cantly more than did retinoic acid (15.8 +/- 0.7 d and 9 +/- 0.8 d, re spectively). While ethanol (vehicle of retinoic acid) slightly but sig nificantly decreased stratum corneum turnover time (p<0.05), water (ve hicle of glycolic acid) did not. This study showed that both glycolic acid and retinoic acid induced certain functional changes in stratum c or neum, mirroring their irritation potential. However, changes at ret inoic acid exposed sites appeared longer-lasting, implying a distinct mode of action. An increase in stratum corneum turnover induced by the substances may be, in part, linked with their irritation properties.