Deodorants and the Microbiome: 9 Common Myths

There are many misconceptions about deodorants, our microbiome and body odour. Together with our partners at Cosmetics Cluster UK (CCUK), we’ve put together 9 common myths surrounding deodorants and the microbiome to explain why they are false!

Myth #1: Our bodies are symmetrical – our microbiome at the left and right part of our body is the same.

False. There can be a difference between the bacterial ecosystem of your left and right armpits. Identical twins do not have the same armpit odour either.

Are you right or left-handed? German and Danish researchers found that bacteria affiliated with Peptoniphilus sp. seems to be active in the right axillae, possibly owing to right handedness causing different environmental conditions – for example aeration, mechanical agitation and secretion of sweat.

Myth #2: Our ‘signature’ armpit odour cannot change.

False. Armpit microbiomes can be transplanted from another person – microbiome transplantation is an emerging new area for treatment of armpit malodour.

Woman in bath towel applying deodorant on armpit

Enjoying this blog? Our webinar with CCUK in April looked at innovation trends and market opportunities in deodorants, translational research in skin microbiome/biofilms, in vitro alternatives to animal testing, new tech and small brand perspectives promoting consumer health and sustainability.

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A researcher in the US decided to see if he could replace the bad BO of one of a pair of twins by ‘transplanting’ the microbial community from his twin. It worked, the twin with BO now smells much better – even after a year! The scientist repeated this procedure with 17 other pairs of close relatives, one sweet smelling one stinky! Before and after the bacterial transplants, the offensiveness of the previously smelly people was judged by a “trained odour panel” of eight people.

Myth #3: There are only a few bacterial species living in the underarm.

False. There are 5 phyla and 99 known species in the microbial community in axilla. Firmicutes (cute name!) are the predominant phylum, accounting for 79.7% of the total bacteria

Staphylococcus and Corynebacterium are the most dominant genera, representing 63% and 3%
hominis (52.4%), S. epidermidis (37.5%) and S. aureus (3.8%) are the three most dominant species within the Staphylococcus genus.

Myth #4: The underarm microbiome stays the same during our lives.

False. Microbiome diversity increases with age! This explains why very old people have a distinct smell!

Colgate-Palmolive investigated this smell, commonly referred to “nursing home smell” or “old people smell”. It seems to be attributed to more than increased diversity of Corynebacteria, the microbe responsible for normal body malodour. Researchers now also understand that underarm odour is ‘unique’ for different age groups.

Myth #5: Sweat always smells.

False. Fresh sweat does not smell. Bacteria break down the compounds, and those ‘breakdown products’ smell. Female sweat is more ‘oniony’ and men’s more ‘cheesy’ – according to a study by the perfume company Firmenich.

Underarm sweat is called apocrine sweat. Apocrine secretions in the armpit contain long‐chain fatty acids, fatty acids bound to amino acids, sulphur‐containing amino acids and hormones, which are too large to become volatile. The bacterial degradation of these compounds leads to smaller compounds, which become volatile and have an odour. Apocrine glands secrete sweat directly into the hair follicle openings in periodical spurts. This sweat mixes with sebum and that is why it comes out as thick, viscous and milky and is the cause of the yellow stains on your white shirt!

Myth #6: Bacteria live on the skin surface in the underarm.

False. Bacteria mostly live, not on the skin’s surface, but are resident inside sweat glands and hair follicles.

Our cultural norm to have neat underarms can lead to frequent shaving or waxing with associated irritation of the moist and warm microbe-rich axilla. Heat and rubbing (hot tubs, excess weight) as well as the use of some deodorants can result in bumps, redness and itching or even infection in the follicles and inflammation in the underarm area.

Myth #7: Underarm hair serves no purpose.

False. Armpit hair may actually help catch you a mate. The hair allows for the odour to linger and the armpits release an odour containing pheromones, a naturally producing chemical that plays a role in sexual attraction. Emotional stress selectively stimulates sweat glands, which is why emotion leads to sudden axillary malodour – this is thought to have been an evolutionary advantage.

Myth #8: Underarm odour is part of modern life.

False. Researchers at the University of York traced the source of underarm odour to a particular enzyme in a certain microbe that lives in the human armpit and it’s there because of an evolution event 60 million years ago, implying that body odour production in humans is an ancient process and has some advantages. You can find out more about emerging technologies in our Deodorant Innovation blog.

Myth #9: Underarm cosmetics do not change the microbiome.

False. The use of underarm cosmetics leads to an increased diversity!

The overall bacterial density is decreased, which opens up space for new species and more diversity – but not all newcomers are beneficial!
It is hypothesized that over usage of underarm products leads to a selective colonization of malodour‐causing microbiota.
Aluminium salts work on eccrine sweat glands but cannot block the apocrine sweat glands and can thus only minimally influence the malodour production.