268 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS specimens were taken from the injected sites of each animal. Two additional control specimens were obtained from each animal. Metabolites were extracted from each specimen with 4 ml of chloroform in a vial for two days at -20øC in order to avoid decompositions of labelled compounds. After the extract was filtered with cotton wool, the flitrate was dried up quickly. Then the residue was redissolved in 1 ml of chloroform. A 0.1 ml aliquot part of this solution was used for liquid scintillation counting with Aloka LSC-601, and the remainder was spotted on a silica gel plate. After developing, the plate was scanned with a radiochromatogram scanner Aloka TLC-2D in order to identify metabolites. After extraction, the specimen was digested and counted for ra- dioactivity by the method of Petroffet a/. (19). RESULTS WHOLE BODY AUTORADIOGRAPHY WITH HAIRLESS MICE The distribution of •4C-labelled IPM, DD, HDO, GTO and OD was assessed by whole body autoradiography with hairless mice sacrificed at 1, 6, 24 and 48 hr after topical ap- plication. Neither neat oils nor those in hydrophilic ointments penetrated into body organs. The oils were still localized on the applied regions 48 hr after application. The autoradiograms at 48 hr after application of oil-containing ointments are shown in Figure 1. MICROAUTORADIOGRAPHY WITH GUINEA PIGS The distribution of five •4C-labelled oils was observed by microautoradiography in the skins of guinea pigs sacrificed at 6 and 24 hr after topical application. Each oil had a characteristic pattern of distribution in the skin depending on application time. The microautoradiograms of these oils are shown in Figure 2. IPA/I. After 6 hr, the transfollicular penetration was observed, which resulted in the concentration of silver grains into the sebaceous glands. The silver grains are derived from and show the distribution of radioactive substance. The grains were distributed in the stratum spinosum. After 24 hr, the grains were distributed densely in the hair in- fundibula, the follicles, the stratum spinosum and particularly the sebaceous glands. Also, the dermis adjacent to them had a slight distribution of grains. GTO. After 6 hr, the silver grains were distributed from the stratum corneum to the sebaceous glands, but not so marked as those in IPM. After 24 hr, however, the grains spread up to the hair bulges and concentrated considerably in the sebaceous glands. The grains were observed slightly in the dermis under the basal layer and around the hair follicles and the sebaceous glands. OD. After 6 hr, the silver grains were distributed a little from the hair infundibula to the sebaceous glands. After 24 hr, those were concentrated in the sebaceous glands and spread to the dermis around them. DD. After 6 hr, the silver grains did not appear in the skin. After 24 hr, the grains were observed slightly from the hair infundibula to the sebaceous glands. This substance was found to be absorbed at a slow rate.

PERCUTANEOUS ABSORPTION OF COSMETIC OILS 269 I PM m HDe GTO m Figure 1. Whole body autoradiograms showing the distribution of radioactivity in hairless mice at 48 hr after topical application of •4C-oil-containing hydrophilic ointments. No oils were penetrated into body organs. The radioactivities of oils were localized on the applied regions. The right of figure is head and the left is tail HDO. The silver grains were not observed in the skin even after 24 hr. It was thought to be absorbed little or at an extremely slow rate. From the results above, the absorbability of the oils was found reasonably in the following order from greatest to least: IPM, GTO, OD, DD and HDO. Therefore, percutaneous absorption on IPM as the highest penetrant and HDO as the lowest was then examined in Angora rabbits by means of microautoradiography more deeply, simultaneously with skin irritation potential by histological method.