322 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS surface and were not readily removed by the wiping procedure. These oils acted as adsorbers for the weak beta particles emitted from the carbon 14 and the radioassay taken after wiping was low due to this adsorption. This effect of the oils is illustrated in Fig. 1. Consequently the formulation containing the oils appeared to be a better cleanser. Other formulas, not possessing materials which would act as adsorbing layers for the radioactive particles, gave a performance rated in proportion to their actual cleansing efficiency. There have been other instances in advertising literature where experimental techniques have cast doubt on the validity of the results. It is obviously very necessary that good experimental design be used and the limitations of the studies be fully realized before attempts are made to draw broad conclusions on results obtained. COSMETIC RESEAr•CH With proper experimental design radiotracer techniques can bc very valuable in furnishing solutions to existing problems. Use of carbon-14 and other radioisotope tagged compounds has aided in determining the meta- bolic fate of additives to formulations in order to facilitate clearance of the materials by the Food and Drug Administration (2). This procedure of metabolic tracing is becoming common practice in the Pharmaceutical and Chemical Industries, and the F.D.A. generally desires the procedure as part of the evidence necessary before condoning the internal use of a com- pound by the general public. Closely related to metabolic tracing are studies conducted on the lower animals to obtain information on products or product ingredients for substantiation of advertising claims or acquisition of knowledge. To illustrate, the amount of retention of formulation additives such as tooth decay inhibitors as well as formulations themselves with respect to time and concentration of material used, has been followed (2, 3). An illustration is given in Fig. 2, showing the use of tracers to study the reten- tion of this type of compound. In this case the carbon-14 tagged additive was incorporated into a dentifrice formulation and by use of a trimmed mascara brush, the teeth of white rats were brushed with the formula in a manner similar to that used by humans. At specific intervals after treat- ment the animals were sacrificed, the oral tissues were cornbusted and sub- sequent radioassay showed the amount of retention of the test material. Another example of this type of experiment is the tracer study conducted for a manufacturer of a vaporizing ointment used as a cold medication (4). Using tritium (radioactive hydrogen) tagged camphor and menthol in the ointment, experiments were conducted on dogs to determine the rate of inhalation of the vaporizing ointment. Also studied was the duration of volatilization of the aromatic oils from the ointment base.

RADIOISOTOPES IN DETERGENT AND COSMETIC RESEARCH 323 ":?•:'• •, •:g• ."-,,..•'...::: '. "'•':"' :-• .. . .,} •,• •,:t, })2 ,• -- •t}}•.'½ ........ (' ,.• . ,..,..•.:.,,. ::. t• •v• :."..?'":" ::•' :q ,•T.. a• :..• ... :•"' -:: '" "• .... :. ... •:i•,.•:•.-----• ...... : ..... • ....... . . •..:•, .•..•. -• .5' ..• ..- .- ,:27'•" ..... . :•: .• ...... :-a .:. ...... . .. ::,..: •... .•. •-•.• ' •: .... .?•': _ ...... .,... :" , . ..... :- ,..,.,. ' • 3. •" :'•"•' ':•& ?-:3, .V ß • ":' :•-i: ' '"' :?- .:• ..... Figur%•. In studies conducted with carbon-14 tagged detergents on human hair, casein and gelatin, the effect of pH, solution concentration and exposure time as well as condition of the substrate (as altered by chemicals) has been determined (5). By exposing hair fibers to solutions of tagged detergents with subsequent preparation of autoradiographs, the mode of penetration of these compounds into the hair fiber has also been followed (5). It is pertinent here to point out that extreme care must be taken in the preparation of autoradiographs associated with human hair or skin. It is possible to cause "exposure" of the film by the hair fiber itself with no radioactivity present, because of chemical reaction between the sulfur