EVALUATION OF ANTIBACTERIAL SOAP BARS 347 this reason alone, MIC data do not offer a means of judiciously selecting any one antibacterial bar soap as being superior. Furthermore, the MIC test completely neglects to take into account the effect of the en- vironment in which the product will be expected to perform its function. Pillsbury (1), one of the pioneers in the field of skin degerming, stated that he was unable to demonstrate that in vitro studies were of value in predicting the antibacterial action of an agent on the skin. The way to determine the degerming effectiveness of a skin degerming product is to measure the reduction in the number of bacteria on the skin of panels of people using the product. Such in vivo methods are feasible and, if properly designed and conducted, can give reproducible and precise results. In Vivo Testing A reliable method for determining the size of the bacterial flora of the skin following various types of surgical scrub regimens was developed by Price (2). The procedure involved a sequence of standardized hand- washings (with brush) and the estimation of the number of bacteria re- moved after each washing. Variations of the basic Price method have been reported (3-5). For the laboratory evaluation of the skin de- germing effectiveness of antibacterial soap bars, a further modification of the basic handwashing method has been developed in this laboratory, which over a period of five years has proved to be a precise and practical investigative tool. A pool of subjects is maintained by supplying individuals with soap bars containing no added antibacterial agents for their hygiene when they are not participating as members of a handwashing panel. Suffi- cient time is allowed between participation in different handwashing tests to permit the bacterial flora of the hands of each individual to return to its normal level. From this pool, test panels of 10 individuals (5 males, 5 females) are drawn as required. During a test, each subject is given a bar of test soap to use at home for all handwashing and bathing and a second bar to keep with him for use during the day. In addition, the panelists wash their hands with the test soap under supervision in the laboratory three times daily according to a prescribed routine. In order to minimize possible extraneous factors, panelists are requested not to expose their hands during the test period to other soap solutions (which might remove the antibacterial compounds from the skin) such as in dishwashing, car

348 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS washing, shampooing, etc. Rubber gloves are provided for use by those participating in such activities. At the beginning of the test on Monday morning, before using the test product, and on the following Friday morning, after exclusive use of the test product for four days, an estimate of the number of bacteria on the skin is made. Four successive standardized handwashings are per- formed in a stream of warm tap water, using a bar soap containing no antibacterial additives. The fifth handwashing (fifth basin) is per- formed using the same procedure, except that it is done in a basin con- taining one liter of sterile distilled water rather than in running tap water. The hands are carefully washed and rinsed into the water in this basin. Aliquot samples of the wash water are immediately taken for bacterial enumeration. Pour plates or filter membrane procedures can be used for enumeration. Raw count data are transformed to logarithms for statistical analysis. Data presented in Table III show the constancy of counts deter- mined over a three-year period when using this handwashing procedure as the analytical tool. The soap used by the panelists was the bar previously described as antibacterial Soap A containing the 2% mixture of BSA, TFC, and TCC. Nine different panels were subjected to the same four-day testing procedure. The number, 1.3 X 106, was included in the table as a reference figure. This bacterial count was obtained from nonantibacterial soap bar users and is an average based on more than 500 individual fifth basin handwashings. Data showing the skin degerming effectiveness of various concentra- tions of the antibacterial ingredient, hexachlorophene, incorporated into a milled soap matrix are presented in Fig. 1. With an increase in con- centration of the antibacterial ingredients, a progressive decrease in the mean number of bacteria recovered in the fifth basin was evident. Figure 2 shows the mean number of bacteria recovered in the fifth basin after use of bar soaps containing as antibacterials the following agents: 2.0% Mercuric iodide 1.0% Hexachlorophene 0.5% 3,4,4'-trichlorocarbanilide plus 0.5% hexachlorophene 0.75• Brominated salicylanilides 1.0% 3,4,4'-trichlorocarbanilide Considerable difference was evident as to their relative effectiveness in reducing the number of bacteria found on the skin.