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j. Cosmet. Sci., 53, 269-282 (September/October 2002) Comparative study of the effects of cosmetic formulations with or without hydroxy acids on hairless mouse epidermis by histopathologic, morphometric, and stereologic evaluation LOCIA HELENA TERENCIANI RODRIGUES and PATRICIA M. B. G. MAIA CAMPOS, Faculty of Pharmaceutical Sciences of Ribeiraio Preto, University of S•o Paulo, Av. do Caf s/n, 14040-903, Ribeiraio Preto, SP, Brazil. Accepted for publication March 15, 2002. Synopsis Hydroxy acids have been extensively used in cosmetic and dermatologic formulations because of their satisfactory results in terms of maintaining a young and healthy skin and in recovering aged skin. The purpose of the present study was to examine whether treatment with glycolic acid, lactic acid, a fruit acids mixture, malic acid ester, or salicylic esters of lipophilic acid produces different cosmetic results and produces changes in hairless mice epidermis. Histopathologic, morphometric, and stereologic studies were carried out to investigate the possible alter- ations caused by formulations containing hydroxy acids or derivatives. Statistical analysis from the results indicate that, under present experimental conditions, formulations containing glycolic acid or lactic acid or a fruit acids mixture or malic acid ester acted on the epidermis, causing a thickening of the epithelium where the basal and spinous layers also showed increased thickness. The cells reached the largest volume, and the nuclei were also more voluminous. The results demonstrate that cosmetic benefits from the use of hydroxy acids are caused by modification of the skin surface, the epidermis. The hydroxy acids were more effective when compared with the control and their derivatives in a mouse model. INTRODUCTION Hydroxy acids (HAs) constitute a class of compounds that exert specific and unique effects on skin structures. They have been shown to have profound effects on keratini- zation and corneocyte cohesion (1,2). The cosmetic effects of HAs on the stratum comeurn include normalization of stratum corneum exfoliation, resulting in an increased plasticization and a decreased formation of dry flaky scales on the surface of the skin (3-6). A thinner stratum corneum is more flexible and compact. Address all correspondence to Dr. Patrfcia M. B. G. Maia Campos. 269