HYDROXY ACIDS IN COSMETIC FORMULATIONS 275 RESULTS The results obtained in this investigation are shown in Tables I and II and Figures 2 and 3. GROUP I (CONTROL) The lining epithelium of the hairless mice epidermis is of the keratinized stratified pavement type. The basal layer is clearly visible, resting on the basement membrane and consisting of low cells with scarce cytoplasm and an ovoid nucleus more lightly stained than the nuclei of more superficial layers. The cells of this layer are well organized and arranged in such a way that the long axis is perpendicular to the basement membrane. .A .. Figure 2. Photomicrographs of skin from a hairless mouse. (A) Control. (B) Application of cream formu- lation. (C) Application of cream formulation containing glycolic acid. (D) Application of cream formulation containing lactic acid. Magnification: x960. Stain: H.E.

276 JOURNAL OF COSMETIC SCIENCE ½ D Figure 3. Photomicrographs of skin from a hairless mouse. (A) Control. (B) Application of cream formu- lation containing fruit acids mixture. (C) Application of cream formulation containing malic acid ester. (D) Application of cream formulation containing salicylic esters of lipophilic acid. Magnification: x960. Stain: H.E. The spinous layer, located above the basal layer, consists of more voluminous cells with nuclei containing sparse chromatin and clearly visible nucleoli. These cells tend to be arranged in such a way that the long axis is parallel to the surface. Above this layer is the granulous layer, whose cells contain keratin-hyaline granules in the cytoplasm. The horny layer is located in the outermost portion and consists of keratin filaments firmly adhering to the granulose layer. The dermis, located immediately below the epidermis, consists of a layer of connective tissue (Figures 2A, 3A). GROUP II (CREAM ONLY) Histology. The horny layer was ortho-keratotic, that is to say, the cells were completely