J. Cosmet. Sci., 61, 247–258 (May/June 2010) 247 Comparative in vivo study of the effi cacy and tolerance of exfoliating agents using refl ectance spectrophotometric methods LUISA RIZZA, GIUSEPPINA FRASCA, CLAUDIA BONINA, and CARMELO PUGLIA, Department of Pharmaceutical Science, School of Pharmacy, University of Catania, Viale A Doria 6, 95125 Catania, Italy. Accepted for publication November 16, 2009. Synopsis The aim of the present study was to compare the effectiveness and the safety of different topical agents (gly- colic acid, mandelic acid, and grape juice acid mixture) in skin exfoliation by objective instrumental meth- ods. To evaluate the exfoliating effects of these substances, a new experimental in vivo protocol based on DHA (dihydroxyacetone)-induced skin pigmentation was used. Skin acceptability towards acid application was investigated by the evaluation of skin erythema induced by topical application of these substances at in- creased concentrations. Furthermore, their photosensitizing effects were evaluated by determining the in- crease in sensitivity to UV-light exposure in cutaneous sites previously treated with acids. These in vivo evaluations were monitored by refl ectance spectophotometry. From the results obtained, we observed the differing capacities of the tested acids to increase the rate of skin regeneration, with a signifi cant reduction in the time required to obtain skin renewal. The study pointed out that glycolic acid (10% w/w) induced a faster skin exfoliation, a more intense erythema, and a higher photosensitizing effect in comparison with the mandelic acid and grape juice acid mixtures. Further evi- dence showed that the mandelic acid and grape juice acid mixtures were able to induce a slower and safer peeling action in comparison with glycolic acid. Finally, our results suggest that the methodologies and protocols used in this study may help in choosing the most appropriate topical agents for skin exfoliating treatments. INTRODUCTION Despite new and emerging modalities in the fi eld of dermatology, chemical peeling holds its own as an effi cacious technique available for treatment of cutaneous diseases and con- ditions and for aesthetic improvement (1,2). Chemical peeling involves the application of one or more chemical exfoliating agents to the skin, resulting in a wound-healing process that can regenerate the epidermis and restore photodamaged, wrinkled, blemished, acne- scarred, or blotchy skin to its original appearance (3,4). A variety of chemical peeling agents are available, such as glycolic acid, trichloroacetic acid, salicylic acid, pyruvic acid, resorcinol preparations, and solid carbon dioxide (5), and new agents are being researched to create new ways of peeling (1).