Some people can run miles and barely smell, while others develop strong body odour within minutes. Surprisingly, this contrast is not just about hygiene or the amount of sweat—it largely comes down to microbes. Tiny bacterial communities living on the skin transform odourless sweat into the characteristic scents that differ from person to person.
Fresh sweat itself carries no significant odour. The unpleasant smell develops only after bacteria metabolise the compounds in human secretions. In other words, body odour is less about sweat and more about the microbes that live on us.
The Hidden World on Our Skin
The human skin is home to an enormous microbial ecosystem—roughly a trillion microorganisms, including bacteria, fungi, and other microbes. Collectively, this makes up the skin microbiome, which varies between individuals and even across different areas of the same body (James et al., 2013).
Why, then, do underarms smell stronger than arms or legs? The difference lies in sweat gland type. Apocrine glands, found in hair-bearing regions like the armpits, produce a protein-rich fluid. Certain microbes, particularly Corynebacterium species, metabolise amino acids such as leucine and isoleucine into volatile fatty acids—sharp-smelling compounds that give armpit odour its intensity.
Interestingly, some people’s microbial populations actually work to their advantage. For example, Staphylococcus hominis can inhibit odour-causing bacteria naturally, acting almost like a built-in deodorant system.
The Chemistry Behind Personal Scent
The transition from odourless sweat to recognisable body odour involves complex chemistry. Underarm secretions contain sulfur-rich precursors, which by themselves are scent-free. When bacteria secrete enzymes such as C–T lyase, these compounds are broken down into molecules like 3-methyl-3-sulfanylhexan-1-ol—a sulfur compound with a striking onion-like smell detectable at very low concentrations (James et al., 2013).
Genetics also shapes this process. Variations in the ABCC11 gene influence what substrates apocrine glands release, in turn dictating which types of bacteria thrive there (Martin et al., 2010). This explains why odour profiles differ by ancestry and why certain populations exhibit little to no underarm odour.
Elsewhere on the body, similar processes occur. The feet, for example, often host Brevibacterium linens, the same bacterium involved in cheese ripening. In the humid, enclosed environment of a shoe, it manufactures sulfur compounds responsible for the familiar smell of sweaty feet. This is why dry socks and well-ventilated footwear are so effective in odour prevention.
Recent Discoveries About Individual Differences
Advances in microbiome research have shed new light on why some people smell less than others. One important finding is that microbial diversity plays a central role. Individuals with more varied bacterial communities on their skin tend to produce milder odours because no single odour-causing pathway dominates (Callewaert et al., 2014).
Age and ethnicity add further complexity. Studies have shown that bacterial composition in the armpit changes significantly across the lifespan and differs between populations (Li et al., 2019). This explains phenomena such as the sudden onset of strong body odour during puberty—triggered not only by hormones but also by shifts in microbial balance.
What This Means for Odour Control
Viewing body odour as a microbial phenomenon opens the door to new approaches in odour management. Current antiperspirants and deodorants mainly work by either masking the smell or eliminating bacteria altogether. However, emerging research is exploring gentler and more targeted strategies.
One promising avenue is probiotic deodorants, which introduce beneficial bacteria that outcompete odour-causing strains. Another is prebiotics, which selectively feed “good” microbes while starving the ones that generate odour. These approaches aim to reshape the microbial ecosystem rather than suppress it indiscriminately.
From a skin health perspective, balance rather than eradication of microbes seems ideal. Complete elimination of bacteria may disrupt skin ecology, whereas encouraging the right microbial mix could reduce unpleasant odours naturally and maintain skin health.
Conclusion
Body odour is not merely a hygiene problem—it reflects a complex interplay between sweat chemistry, microbial activity, and human genetics. Each person’s scent is shaped by factors ranging from the ABCC11 gene to the specific microbes on their skin, making body odour as unique as a fingerprint.
As research continues, we may move away from simply masking odours toward cultivating a healthier microbial balance. Ultimately, the way we smell offers a window into the intimate partnership between humans and the microbes we carry. Appreciating this relationship allows us to see odour not as a flaw, but as a reflection of individuality on a microscopic scale.
References
- Callewaert, C., Hutapea, P., Van de Wiele, T., & Boon, N. (2014). Deodorants and antiperspirants affect the axillary bacterial community. Archives of Dermatological Research, 306(8), 701–710.
- James, A. G., Austin, C. J., Cox, D. S., Taylor, D., & Calvert, R. (2013). Microbiological and biochemical origins of human axillary odour. FEMS Microbiology Ecology, 83(3), 527–540.
- Li, M., Budding, A. E., van der Lugt-Degen, M., Du-Thumm, L., Vandeven, M., & Fan, A. (2019). The influence of age, gender and race/ethnicity on the composition of the human axillary microbiome. International Journal of Cosmetic Science, 41(4), 371– 377.
- Martin, A., Saathoff, M., Kuhn, F., Max, H., Terstegen, L., & Natsch, A. (2010). A functional ABCC11 allele is essential in the biochemical formation of human axillary odour. Journal of Investigative Dermatology, 130(2), 529– 540.