Armpit body odor research

Armpit microbiome transplant

We have done a series of clinical trials on armpit microbial transplants in order to solve armpit body odor. We simply replace the malodorous armpit microbiome with a healthy non-odorous microbiome. The donor is usually a close family member. He/she stops washing the armpits for 3-4 days, so we have a large amount of donor bacteria. The donor bacteria are also screening using molecular techniques to verify if the ‘good’ microbes are there. The acceptor washes the armpits thoroughly for 1 week, using soaps, antibacterial washes, and sometimes topical antibiotics. The microbiome is transferred as fresh as possible. We have tested this on about 18 people thus far. Results look very promising – we found significant improvements in armpit body odor for minimum a month. Preliminary findings were reported in Experimental Dermatology.

Probiotic deodorant 

We are now developing a new way to apply to ‘good microbes’ in the armpit, so they can outcompete the ‘bad’ ones, in order to solve armpit body odor. We are doing this by applying the characterized non-odorous bacteria in a spray – and this can be applied on a daily basis. This gives a more sustained application of the ‘good’ bacteria, because we noticed that the effect of the transplant could go away after a couple of months. We have tested this on about 90 people and the last clinical trial was on 63 people. The first results look great! We are still developing and analyzing the results. If you wish to try out one of our testers, or if you want to receive updates on the developments, leave your email address below. We are constantly looking for people that want to participate.

Probiotic clothing

Together with designer Rosie Broadhead, we are exploring the benefits of encapsulated probiotic bacteria into the fibers of clothes. They become activate when they come in contact with moisture on skin. We have clinical data showing that these bacteria are very efficient to fight off body odor. For optimal results, the probiotics are strategically placed in key areas where there is more sweat. The encapsulated bacteria reduce body odor, encourage cell renewal, and improve the skin’s immune system. We are currently in the stage of development. Very excited about this!

Impact of skin care products on skin microbiome and metabolome

At the University of California San Diego, we have tested the impact of sunscreen (on face), skin moisturizer (on arms), foot powder (on feet), and antiperspirant (in the armpit) on the skin microbiome and chemistry.

Specifically the impact of foot powder and antiperspirants was huge on the skin microbiome. The bacterial diversity increased a lot during the use. The dominant bacteria Staphylococcus and Corynebacterium decreased a lot during use while other low-abundant (often malodorous) bacteria increased in abundance during usage. Most people’s skin microbiome went back to their initial skin microbiome after the experiments. Some participants, however, also had worse smelling armpits and feet after the whole experiment. The use of these products remains tricky: it is a biological murder. While most people will not have huge problems, for some people it has long-lasting and unpleasant consequences. The impact of sunscreen and skin moisturizers was very low on the skin microbiome, although the chemical diversity increased.

Many ingredients of skin cosmetics can persist on skin for days and weeks after its last use. Examples are: Polyethylene glycol (PEG) that persists for 0.5 weeks on skin; Polypropylene glycol (PPG) that persists for 1-3 weeks on skin; Skin lotion lipids persists for 1.2 weeks on skin, while the participants took a daily shower and used no cosmetics at all during the period of sampling. Skin hormones/steroids change with the use of antiperspirants. Almost all hormones decreased during the use of antiperspirants. The aluminum salts block the sweat pores, and as such no more steroids are excreted. Some hormones were also upregulated, because of the hugely shifted underarm microbiome. Examples include androsterone, androstenedione, androstanolone, androstenedione.

Skin care products are widely used, and some ingredients can have far-reaching impacts. For the most part and for most people, there is no problem to use them. The skin microbiome and metabolome is strong and resilient enough to endure these external perturbations.

The full article can be found here: BMC Biology.

Staphylococcus and Corynebacterium in the human axillary region

Until recently, the human armpit was a piece of mystery. Therefore, this research studied the bacterial flora in the armpit by sampling over 50 people and resampling some of them during a year. Two bacterial genera always occurred in the armpit: staphylococci and corynebacteria. About 77% of all sequences were assigned to those two bacterial groups. The corynebacteria are known to cause armpit body odor. The staphylococci are known to cause no significant malodor.

The research showed that, although the number of bacteria can go very high, the number of different bacteria was rather low. On average, about 100 different bacterial OTUs occur in the armpit. Which is much less than other body site, like the forearm, legs, face or hands. 

With use of more deodorant, the bacterial diversity increases in the armpit. How do I understand this? If you don’t use deodorant, and you don’t wash yourself too often, very few different bacteria will occur there. If you do not have smelly armpits: keep it like that and don’t overuse deodorants. Because, if you’re using a lot of deodorants, more different bacteria will occur, and if one of those bacteria is an odor-causing bacterium, and he can suddenly take over, smelly armpits will be the results.

Female armpits contain more staphylococci, while males are likely to have more corynebacteria in the armpit. This is due to the fact that males have a thicker skin and sweat more fatty substances in the armpit, which is the favorite dish for the lipophilic corynebacteria.

It is likely that your left armpit is not identical to your right armpit. Small bacterial differences occur between left and right armpit in the half of the studied people. Only in some cases, this can express in a different odor between left and right armpit. The bacterial community is quite stable over time, although a total shift was seen for both armpits for two people. The reason for this shift is still unknown, however, this implies that the armpit microbiome is able to reconfigure to another stable microbiome, and maybe into a less odorous armpit. Our research team is doing anything within our power to make this possible for other people and to find solutions for armpit body odor.

The full article can be found in Plos One

The effect of deodorants and antitranspirants on the armpit microbiome

The majority of the people use or have an underarm deodorant or antiperspirant. We studied the effect of deodorants and antiperspirants on the armpit microbiology. Significant changes are seen when deodorants and especially antiperspirants are used. We asked eight people, who used underarm cosmetics on a daily basis, to restrain from using any deodorant/antiperspirant during one month. Another person, who did not use any underarm cosmetics was asked to start using a daily deodorant during one month. When deodorant/antiperspirant is used in a stable manner, the microbiome is quite stable over time. When the usage is stopped or resumed, we saw big changes in the axillary microbiome. Especially antiperspirants have a significant effect on the microbiome. The diversity increases and an increase of the Actinobacteria phylum is seen, containing the odor-causing Corynebacterium species. If the Corynebacterium spp. become more dominant, the subjects armpit body odor can increase and change to a more sour/musky odor. Aluminum salts in the antiperspirants likely have a higher impact on the Staphylococcus spp. than the Corynebacterium spp. 

The full article can be found in Archives of Dermatological Research; or download pdf here; news stories about it can be found in RealClearSciencethe Huffington Post and the Washington Post.

The malodorous armpit microbiome

We have screened over 200 people with self-reported armpit body odor. We analyzed the microbiome, the odor and the effect of the malodor on their daily lives. The results are astonishing; we received a full and profound view on the the malodorous microbiome and its effects. Currently working on this paper. For now just remember: if you have armpit body odor, it is not your mistake: it is the cause of your bacteria.

The bacterial and odor profile of sport clothes

After sports, sport clothes can get quite smelly. Some people may have noticed that the type of clothing textile also has an influence on armpit body odor formation. Our research team investigated this and has identified the typical odor causing textile types, but also the bacterial strains responsible for this odor. Polyester clothes smell worse than cotton, following intensive exercise by their wearers, because bacteria that cause odor grow better on polyester. We collected t-shirts from 26 healthy individuals following an intensive, hour-long bicycle spinning session. These were incubated for 28 hours before having them inspected by a trained odor panel. We also investigated the taxonomy of the bacteria on the shirts and in the axillae.

Freshly secreted sweat has little odor, because the long-chain fatty acids the axillae secrete are too big to be volatile. Bacteria break these, as well as hormones and sulfur compounds, down to smaller, odoriferous molecules. We particularly found micrococci able to grow on the polyester clothing textiles. This finding was confirmed in an in vitro experiment. The below figure shows enrichment or inhibition off specific bacteria on different clothes.

Micrococci are known for their enzymatic potential to transform long-chain fatty acids, hormones, and amino acids into smaller, volatile, compounds, which have a typical malodor. Staphylococci, which inhabit both axillary skin and adjacent textiles (the latter with much less diversity), create a normal, non-malodorous armpit body odor. Interestingly, corynebacteria, which are the main cause for malodor in the armpits, were not able to grow on the textiles. Apparently, they need the more anaerobic environment of the human skin to grow. 

The article can be found in Applied and Environmental Microbiology; news stories can be found in Popular ScienceAAAS Science magazineNPRScientific American and nu.nl.

Artificial sweat composition 

In our armpit research we have succeeded in making an artificial sweat composition. Yeej! And why do we what to do that? Simple: every person is different, and we need an objective method that does not have the variations every human being has. Based on literature, we composed a sweat composition which permits all armpit bacteria to grow in equal manners as they would do on the armpit skin. The axillary bacteria still resemble the original community after growing them for 21 days in the artificial sweat composition. Even the formed odor and malodor molecules resemble the original odors. 

The full article can be found in Journal of Microbiological Methods; or download pdf here.

Bacterial exchange in washing machines

In the past decennia, there was an evolution towards lower washing temperatures and mild, eco-friendly washing detergents. This is good for the environment, but the impact on the bacteria was not yet known. Unpleasant odors can still be present even after washing your clothes in the laundry machine.

Bacteria stick to the clothes after washing at 30°C and with mild detergents, and are only partially removed. The laundry machine causes a microbial exchange, where the bacteria of the dirty laundry is transferred on other clothes. Washed clothes typically attracted specific skin- and clothes-related bacteria. Certain species have a higher affinity to adhere to the clothing textiles than others.

Up to 1 million living bacteria are found per milliliter of effluent water after laundering. Only low amounts of bacteria from the influent water were retrieved in the cotton pieces, even when recycled rainwater was used (known to contain large amounts of bacteria). The water-related bacteria are predominantly found in the effluent water.

Ever wondered why clothes always develop the same odor? This is because the clothes develop their own microbiome. The same odor-causing bacteria return after laundering, and can cause a specific odor when the clothes are used again. The odor-causing bacteria adhere very well to the clothes and are not washed out with the washing machine. 

The full open-access article is available at Frontiers in Microbiology

Other research

Algorithmic Learning for Auto-deconvolution of GC-MS Data to Enable Molecular Networking within GNPS

Nature Microbiology – Home chemical and microbial transitions across urbanization

Experimental Dermatology – Towards a bacterial treatment for armpit malodour

Nature Reviews Microbiology – Best practices for analysing microbiomes

Annual Review of Pharmacology and Toxicology – Impacts of the Human Gut Microbiome on Therapeutics

Annual Review of Genomics and Human Genetics – The Microbiome and Human Biology

mSystems – American Gut: an Open Platform for Citizen Science Microbiome Research

Journal of Investigative Dermatology – IL-4Rα Blockade by Dupilumab Decreases Staphylococcus aureus Colonization and Increases Microbial Diversity in Atopic Dermatitis

mSystems – A Microbiome-Based Index for Assessing Skin Health and Treatment Effects for Atopic Dermatitis in Children

New Biotechnology – Novel biocompatible nanocapsules for slow release of fragrances on the human skin

Full scientific résumé: Google Scholar