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j. Cosmet. sci., 50, 159-170 (May/June 1999) Histopathological, morphometric, and stereologic studies of dermocosmetic skin formulations containing vitamin A and/or glycolic acid PATRICIA MARIA BERARDO GON(•ALVES MAIA CAMPOS, GISLAINE RICCI, MARISA SEMPRINI, and RUBERVAL A. LOPES, Faculty of Pharmaceutical Sciences of Ribeira7o Preto (P.M. B. G. M.C., G.R.) and Dental School of Ribeir•o Preto (M.S., R.A.L.), University of Sa7o Paulo, Sa7o Paulo, Brazil. Accepted for publication April 3 O, 1999. Synopsis Among the many active agents for dermocosmetic purposes that have been described, marketed, and prescribed, vitamins (vitamin A palmitate among them) and alpha-hydroxy acids such as glycolic acid have been gaining scientific importance. Vitamin A palmitate contributes to the maintenance of skin softness and smoothness, improving the water barrier properties of the tissue. Glycolic acid has yielded highly satisfac- tory results in terms of recovery of aged skin. The combination of low concentrations of glycolic acid with vitamin A palmitate has been extensively used in dermocosmetic formulations. The objective of the present study was to investigate the histopathological alterations caused by formulations containing vitamin A and/or glycolic acid in guinea pig skin, determined by appropriate stereologic techniques. The following formulations were applied to specific shaved areas of guinea pig skin: gel alone (used as the dermocosmetic base), gel with vitamin A added, gel with glycolic acid added, and gel with both vitamin A and glycolic acid added. After application of the formulations for one week, skin biopsies were obtained from the animals and we investigated the histopathological alterations. Under the present experimental conditions, both the formulations containing vitamin A and glycolic acid caused increased epidermal thickness, with cells of larger volume due to intra- and extracellular edema (hydration). This epithelial thickening was not limited to the upper cell layers but was also present in the basal and spinous layers. These alterations were even more evident with the use of the formulation con- taining a combination of vitamin A and glycolic acid. INTRODUCTION Among the countless active principles used for dermocosmetic purposes, vitamins (and vitamin A palmitate among them) and alpha-hydroxy acids (such as glycolic acid) have gained notoriety due to their pharmacodynamic properties (1). Alpha-hydroxy acids, a group of natural substances found in fruits and in other foods, have been widely used by the cosmetics industry for the preparation of anti-aging skin formulations. 159