Bacterial flora: the origin of the scent of our armpits

The bacteria of the axillary cutaneous flora are thought to influence the odor which emanates from our armpits... Scents which might have less to do with quality than quantity, and perhaps linked to age, according to a Japanese study.

 

Tell me how your armpits smell and I will tell you which bacteria live there. Sweat does not have an odor, but enzymes produced by the bacteria which populate our underarm area transform various bodily substances (proteins, fatty acids, lactic acid, skin lipids…) into sometimes foul-smelling aromas.

Milk or cumin: two Japanese types

Researchers attempted to characterize this axillary cutaneous flora in some twenty Japanese men with an average age of 37, divided into two groups according to the odor emanating from their armpits: C for “cumin”, a strong spicy smell; and M for “milky”, a more neutral odor, close to that of milk or skin. Note that this classification was performed by four experts charged with the task of carrying out a direct olfactory assessment–sometimes science is a matter for the passionate. The participants were subsequently subjected to a protocol that was quite rigorous: no use of deodorant during the three days preceding the collection of samples of flora, no bath, or spicy food, or alcoholic drink the evening before, no cigarettes on the day itself.

A particular case

The researchers observed that the axillary flora of these two groups was similar, with a predominance of the genera  Anaerococcus, Corynebacterium, Staphylococcus, Moraxella and Peptoniphilus. Except for one individual in group C, the youngest (18 years old) in this small cohort, who presented with a flora composed mostly of Staphylococcus. Enough to suggest that age could influence the microbial composition–and therefore the odor–of male armpits. As French tragedian Pierre Corneille said “In souls nobly born, valor does not depend upon age”: the same happens to spicy axillary odor, much to the displeasure of those with sensitive noses.

A public health issue

In reality, the odors emanating from the axillae are likely to depend less on bacterial composition than on volume: subjects with a cumin-like odor hosted more bacteria than subjects with a more neutral odor. Although these results partially agree with those of recent studies conducted in Germany, Belgium and Switzerland (Japan is not the only country interested in this subject), the authors call for this type of research to be extended to identify any determining factors of axillary odor linked to ethnic origin or gender. A research theme that is far from being trivial for the cosmetic and hygiene products industry, particularly in the Land of the Rising Sun, where the war against odors verges on being a national sport.

 

Sources:

Okamoto H et al., Characterization of the Axillary Microbiota of Japanese Male Subjects with Spicy and Milky Odor Types by Pyrosequencing, Biocontrol Sci 2018 ;23(1):1-5