The hairless mouse as a model for quantitating skin deposition of 3,4,4'-trichlorocarbanilide in bar soap

A method is described for quantitating the deposition of the germicide 3,4,4'-trichlorocarbanilide (TCC) via direct application of bar soap to the skin. The soap contained 1.5% [14C]TCC. Quantitating the skin deposition of biologically active materials is important in the safety evaluation of these ingredients as well as the finished products. In the case of rinse-off products such as soaps, the residue remaining after rinsing constitutes the major portion of material available for penetration. The hairless mouse and the clipped albino Sprague-Dawley rat were evaluated as models for human skin deposition. Little TCC remained on the skin of either species following the wash and rinse procedure. The amount deposited on rat skin was 1.5% of the applied dose or 0.87 micrograms TCC/cm2 while the amount deposited on hairless mouse skin was 1.1% or 0.18 micrograms TCC/cm2. The greater deposition of TCC onto rat skin was likely to be due to the presence of a greater amount of hair. Results obtained using the hairless mouse were consistent and reproducible. The hairless mouse does not require shaving and is easy to handle. Since, like man, it has little hair, it appears to be an excellent model for use in predicting the deposition of TCC on human skin.