Magnus S. Ågren, Khaled S.A. Ghathian, Amalie K.S. Frederiksen, Morten J. Bjerrum, Henrik Calum, Patricia L. Danielsen, Jyoti Menon, Merete Hædersdal, Lars N. Jorgensen
DOI: 10.2340/00015555-3499

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 1 axilla was treated with zinc oxide and the other with a placebo for 13 days. The microbiota and pH were analysed 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.

Corynebacterium spp. thrive in the intertriginous axilla, and can cause malodour. Zinc oxide is a mild antiseptic compound effective against Gram-positive organisms. In healthy volunteers, this study found that, compared with a placebo, zinc oxide formulated in an oil-in-water emulsion reduced the counts of aerobic microbiota, including corynebacteria, and decreased self-evaluated axillary malodour. The isolated Corynebacterium spp. showed reduced survival at pH 5.0 and susceptibility to zinc oxide in vitro. This study provides novel data that may prove useful for basic microbiome research and the development of efficient deodorant products for the axilla.