February 2022 • Vol. 28 • Issue 2
Underarm Products and the Skin Microbiome
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by Phil Klepak and Barbara Schmidt
oday, everyone is talking about the skin microbiome—scientists, product formulators, doctors, consumers, beauty editors, and more. But the skin microbiome is a relatively new term to most people. Even in the scientific and medical fields, it has only become a hot topic in recent years. The cosmetics industry has now begun serious research into the skin microbiome, using this knowledge to change how we protect our skin and overall health. Why is studying the skin microbiome important? In simple terms, the skin microbiome is defined as the collection of all microorganisms living on the skin. Studying the microbiome at different body sites can elucidate the aetiology of common disorders, which are often site-specific, such as acne, eczema, psoriasis, underarm malodor, etc. Also, a balanced microbiome is believed to be critical and integral to maintaining normal skin barrier function, thereby allowing the skin to appear and feel healthy. The cosmetics industry is leveraging the skin microbiome concept from the point of view of developing new products that foster healthy skin, but clinical support for the efficacy of these products still needs to be generated. This article is a review of the axillary microbiome, focusing on the positive and negative effects of underarm products and ingredients.
n The Axillary Microbiome and Malodor
Human axillary odor is commonly attributed to the bacterial degradation and metabolization of odorless eccrine, apocrine, and sebaceous gland secretions into volatile odorous compounds or odor agonists. The chemical classes implicated in axillary malodor (AKA body odor) are short chain volatile fatty acids (e.g., 3-methyl-2-hexenoic acid), steroidal compounds (e.g., androstenone), and thioalcohols.1 Human axilla microbiology and its relationship to malodor have been studied for at least 50 years. Early work showed the axillary flora was a stable mixture of micrococci, aerobic diphtheroids (e.g., corynebacteria), and propionibacteria, with the aerobic diphtheroids recovered in high numbers in all subjects having typical body odor.2 Others have also performed detailed characterization of the underarm microflora, and confirmed four principal gram-positive groups (staphylococci, aerobic coryneforms, micrococci, and propionibacteria), and the yeast genus Malassezia.3 Subsequent work showed that no one group of organisms continuously dominates the population, but changes in the population density of Corynebacterium spp. was dominant especially for the detection of odor. Further, there were colonization differences between the right and left axillas possibly due to difference in nutrient availability.4 It is generally believed that the microbial flora is quantitatively stable with a high or low count being an inherent individual characteristic. Mapping studies of the axillary microbiota using rRNA gene sequencing showed significant variations between males and females. Male armpits were characterized with more Corynebacterium spp. and less Staphylococcus spp. compared to female armpits.5,6 The overall evidence correlates “bad” underarm odor with Corynebacterium spp., while “good” odor levels are associated with a (continued on Page 6) predominance of Staphylococcus spp.1,7
ARTIFICIAL INTELLIGENCE AND ITS APPLICATION IN PERSONAL CARE ...see pages 4-5 for more information.