272 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 4. Light micrographs showing the histological feature in the skin of Angora rabbits after topical ap- plication of •4C-IPM. A) intact skin, B) 2 hr, C) 6 hr, D) 24 hr. The changes of cells in the epidermis and collagen fibers in the dermis and the infiltration ofpolymorphonuclear leucocytes were observed the hair bulges became concentrated during the period of application and, further, the distribution was spread to the deep regions of the hair follicles. Simultaneously, the surrounding dermis had an increasing distribution of grains. Also, the diffusion of grains from the epidermis down to the dermis appeared increased (Figure 5). 2. Histology: marked changes in the epidermis and the dermis were scarcely observed at 2 and 6 hr. The epidermis was composed of two or three layers and each cell became swollen and round. Weak edema was seen at 24 hr together with slightly increasing infiltration of small mononuclear leucocytes in the upper layers of the dermis. Vasodi- latation or hemorrhage were not observed (Figure 6). The results indicated that the irritation potential of HDO was extremely low. OBSERVATION OF FATE WITHIN SKIN The patterns of the distribution and the skin irritation potentials of •4C-labelled IPM and HDO were observed by microautoradiography and histological method in the skins of Angora rabbits sacrificed at zero, one, three, six and ten days after 24 hr topical application. IPM. 1. Microautoradiography: IPM was distributed into the skin both transeptider- mally and transfollicularly immediately after 24 hr application. The density of grains in the epidermis and the hair follicles was maximal at one day after the finish of applica-

PERCUTANEOUS ABSORPTION OF COSMETIC OILS 273 Figure 5. Microautoradiograms showing the distribution of radioactivity in the skin of Angora rabbits after topical application of •4C-HDO. A) 2 hr, B) 6 hr, C) 24 hr. Note the concentration in the sebaceous glands and epidermis