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j. Soc. Cosmet. Chem., 34, 351-359 (November 1983) Application of a new microbiological technique to the study of antiperspirant and deodorant soap efficacy R. F. THEILER, C. L. SCHMIT, andJ. R. ROHEIM, Armour Research Center, New Science and Technology Department, 15101 N. Scottsdale Road, Scottsdale, AZ 85260. Received January 10, 1983. Synopsis A new technique for sampling cutaneous microorganisms has been used to study the effects of deodorant products on aerobic axillary microbial populations. Initially the Thran spray gun was compared to the mechanical scrub method and was found to compare favorably in terms of reproducibility and sensitivity. When a commercial stick antiperspirant was evaluated, both methods demonstrated similar log reductions in axillary bacteria when compared to controls. The Thran spray gun was also used to study the efficacy of a commercial deodorant soap containing 3,4,4'-trichlorocarbanilide. A 55% reduction in aerobic axillary microorganisms was demonstrated 24 hours after washing with the soap. INTRODUCTION Many locations on the surface of human skin emit distinctly different odors. However, of all the human scents, those emanating from the axilla are regarded by society as some of the most offensive. In recent years the accumulation of a significant body of scientific evidence has traced the source of axillary odors to the action of bacteria on secretions from the apocrine gland (!-4). In a number of recent publications it has been suggested that a class of Gram positive microorganisms, the diphtheroids, are responsible for the selective generation of the distinctly pungent axillary odors, while the micrococci are responsible for the generation of sweaty, acid odors (2-4). Therefore, numerous manufacturers of deodorant products have marketed formula- tions with an active ingredient which reduces axillary microbial populations for the purpose of reducing the intensity of axillary odor. Since bacterial reduction is related to a product's deodorant efficacy, numerous methods have been developed for qualitatively and quantitatively monitoring the distribution and population of skin flora. Among these are mechanical scrub techniques (5-6), swabbing procedures (7-9), tape stripping and contact plates (7-13), as well as basin scrubbing methods (14-15). Among these techniques, a widely employed procedure for quantitating aerobic skin micro flora has been the mechanical scrub technique which involves a timed scrub of the skin surface with a blunt teflon scrubber 351