3: Final Report on the Safety Assessment of Methylene Chloride

Abstract

MeCl2 is a volatile compound that, if applied as an aerosol, would not remain on the skin for an extended period of time. However, certain cosmetic products that contain MeCl2 are designed to remain on the skin and thus may expose the skin to MeCl2 for longer time periods. It has been estimated that the use of hair sprays containing MeCl2 could expose the user to MeCl2 concentrations ranging from 1 to 154 μg/liter of air. MeCl2 was irritating to the skin of animals; an antiperspirant and a deodorant containing MeCl2 were mildly irritating to the skin of humans. Limited data obtained from animal and human studies indicated that MeCl2 did not induce sensitization. No data were available on whether MeCl2, when applied in a medium designed to remain on the skin is or is not a sensitizer. MeCl2 does not absorb UV-A or UV-B light; therefore, it is unlikely to be a phototoxic agent. In seven different laboratory studies with sufficient animals to permit meaningful statistical analysis of the data, only the results from a chronic mouse study indicated that MeCl2 is a carcinogen. The results of pharmacokinetic and metabolism studies established that the metabolism of MeCl2 in the mouse differs quantitatively from that in the other species studied, and this difference in metabolism could account for the positive tumorigenic response in the mouse. The available epidemiologic studies did not indicate a difference in cancer rates between exposed and unexposed groups. To conclude that the one positive carcinogenicity study is of greater significance in safety evaluation than the six negative carcinogenicity studies, it would be necessary to exclude the results of the pharmacokinetic, metabolism, and epidemiologic studies that support the conclusion that MeCl2 is not a carcinogen for humans and other animal species. Considering all the data, in particular the pharmacokinetic and metabolism data, it is concluded that the data are insufficient to establish MeCl2 as a human carcinogen. Further, it is also concluded that the positive carcinogenic response obtained in the mouse study cannot be extrapolated to humans. The evidence is that MeCl2 is a carcinogen for mice but is not carcinogenic for rats, hamsters, or humans. Because of the lack of human skin irritation and sensitization data on cosmetic products containing MeCl2, the safety conclusion is restricted to aerosol products in which the duration of exposure (skin contact) is limited by the rapid evaporation of MeCl2 from the skin. On the basis of the data included in this report, it is concluded that MeCl2 is safe for use in cosmetic products designed for brief discontinuous use.