338 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 2. Photomicrograph of fine particle size (0.1 Ixm) zinc oxide. The zinc oxide particles aggregate to form a massive lump. products. It also has a fairly rough texture, which may feel uncomfortable when applied to sensitive skin. The whiteness of zinc oxide is often considered too vivid in contrast to skin color and may be emphasized when applied to exposed parts of the body. To overcome such shortcomings, we attempted to form a composite or "hybrid" powder, Table I Formulae of Body Odor Quenchers Formula Ingredients 1 2 3 4 AHC 0 0 3O 3O Talc 50 50 35 50 ZnO/nylon (20%) 0 30 15 0 ZnO 30 0 0 0 S. microbeads 20 20 20 20 The content of each ingredient in the powder is shown in weight percent.

NOVEL POWDER DEODORANT 339 which consists of a spherical nylon as the core powder, the surface of which is uniformly covered with fine-particled zinc oxide. To 80 parts of nylon 12 powder (average particle size 6.6 •xm, Nikko Rica Corp.), 20 parts of zinc oxide (average particle size 0.1 •xm, Sakai Kagaku Kogyo) were added and mixed together in a Henschel mixer (Mitsui Miike Machinery Co., Ltd., Model 10B) for five minutes. The mixture was placed inside a tumbling mill (Retsch, Model S2) charged with alumina balls (0.8-30 mm i.d.), where it was mixed and compressed for 30 to 60 minutes. EFFICACY OF QUENCHERS FORMULATED WITH HYBRID POWDER ON FOOT ODOR Efficacy of body odor quenchers in the form of aerosols was assessed. Four quenchers, whose powder parts formulae are shown in Table I, were prepared for the assessment. Our panel consisted of six subjects (six men, 20 to 30 years old) with fairly strong foot odor, all from our laboratory. For each formula the assessment was carried out in the following manner. First of all, the six subjects self-evaluated their right and left feet, based on a five-step foot odor intensity: 0, no foot odor 1, faint foot odor 2, medium foot odor 3, strong foot odor 4, extremely strong foot odor. After evaluation, the quencher was applied to the foot possessing the stronger foot odor, and the other foot was left untreated. The quencher was always applied only on the former foot during the assessment, and the latter was left as control. The quencher was applied twice a day for two days. Foot odor was self-evaluated just before applying the quencher. An example of such an assessment procedure is shown in Figure 3. As shown 8/9 9:00 8/9 13:00 8/10 9:00 8/10 13:00 selection of foot for applying the quencher (olfactory evaluation) • first applicatio olfactory evaluation second applicatio olfactory evaluation I--- third application olfactory evaluation fourth applicatio 8/10 16:00 Figure 3. Assessment procedure for body odor quenchers on foot odor. The assessment lasts for two days during which four applications and five evaluations are accomplished. olfactory evaluation