Zinc Oxide Inhibits Axillary Colonization by Members of the Genus Corynebacterium and Attenuates Self-perceived Malodour: A Randomized, Double-blind, Placebo-controlled Trial

Malodour from the axilla is commonly caused by specific microbes, and may be inhibited by zinc oxide. The aim of this study was to determine the effects of zinc oxide on the axillary microbiota, odour and pH in a randomized, double-blind, placebo-controlled trial in 30 healthy volunteers. In each participant one axilla was treated with zinc oxide and the other with a placebo for 13 days. The microbiota and pH were ana-lysed before and during treatment. At the final visit, the participants judged their own axillary odour for comparison. With zinc oxide treatment total bacterial growth and, specifically, that of odour-producing Corynebacterium spp. and Staphylococcus hominis, decreased (p<0.05), despite an increase (p<0.0005) in skin-surface pH. Compared with the placebo, zinc oxide treatment reduced (p = 0.005) self-perceived malodour. In vitro, Corynebacterium spp. (19 isolated strains) survival was reduced (p<0.0005) at pH 5.0 compared with pH 6.0; growth inhibition by zinc oxide occurred at ≤400 mg/l, and cell death occurred at ≤10,000 mg/l for 12 (63%) of the strains. In conclusion, application of zinc oxide reduced malodour and the counts of causative bacteria, but increased the pH of the axilla.