Research
Body Odor and the Skin Microbiome: The Science
Underarm sweat, as it leaves the body, is essentially odorless. The smell we recognize as body odor is made by the community of bacteria living on the skin, chiefly Corynebacterium and Staphylococcus species, which biotransform the odorless secretions of the apocrine glands into small, highly volatile molecules such as thioalcohols, short-chain fatty acids, and steroid-derived compounds. This page summarizes the verified microbiology of axillary (underarm) odor: which bacteria dominate the underarm, which molecules they produce, and what recent enzymology has revealed about how the smell is made.
By the Sweat Explained Editorial Team · Published 2026-07-13 · Last reviewed 2026-07-13 · Educational information, not medical advice.
Key statistics at a glance
76.7%
of underarm bacterial sequences belonged to just two genera: Corynebacterium and Staphylococcus
Callewaert 2013 (53 subjects)
3 classes
of malodour molecules from apocrine substrate: volatile fatty acids, 16-androstene steroids, and thioalcohols
James 2013 review
S. hominis
a key producer of the potent thioalcohol 3M3SH from an odorless precursor
Minhas 2018
87% / 39%
of women clustered in a Staphylococcus-dominated underarm community vs 39% of men in a Corynebacterium-dominated one
Callewaert 2013
Sweat itself is odorless: bacteria make the smell
Two things have to happen for underarm odor to form. First, the apocrine glands (concentrated in the underarm and groin) secrete a viscous, protein- and lipid-rich fluid that is itself effectively odorless. Second, bacteria living on the skin take up components of that fluid and enzymatically convert them into small volatile molecules that our noses detect. Without the microbial step, there is very little smell.
This is why body odor is best understood as a product of the skin microbiome rather than of sweat alone. The 2013 review by James and colleagues describes the process as "microbial biotransformation of odourless natural secretions into volatile odorous molecules," and identifies members of the genus Corynebacterium as the primary causal agents of underarm odor.
Association here is mechanistic, not incidental: specific bacterial species carry the enzymes and transporters needed to release specific odor molecules, and the composition of a person's underarm community shapes the character of their odor.
Who lives in the underarm
The underarm is a warm, moist, nutrient-rich niche colonized by a relatively small set of bacterial groups. In a study of 53 healthy adults, the great majority of sequences belonged to just three bacterial phyla, dominated by the Actinobacteria (which include Corynebacterium).
| Group | Value |
|---|---|
| Actinobacteria (incl. Corynebacterium) | 59.7% |
| Firmicutes (incl. Staphylococcus) | 23.2% |
| Proteobacteria | 16.7% |
Source: Callewaert et al., PLoS One 2013;8(8):e70538. Chart is an original rendering of the cited data.
The three main classes of odor molecules
Underarm odor is not one chemical but a blend. Reviews of the axillary odor literature consistently group the key contributors into three molecular classes, each generated by bacterial action on a different apocrine substrate.
| Molecule class | Character | Bacteria implicated |
|---|---|---|
| Thioalcohols (e.g. 3-methyl-3-sulfanylhexan-1-ol, 3M3SH) | Sulphurous, onion-like; extremely potent | Certain Staphylococcus species (e.g. S. hominis) |
| Short- and medium-chain volatile fatty acids (e.g. 3-methyl-2-hexenoic acid) | Sour, pungent | Corynebacterium species |
| 16-Androstene steroids (e.g. androstenone, androstenol) | Musky, urinous | Corynebacterium species |
Compiled from James 2013 (review) and Minhas 2018 (thioalcohol pathway). The same person's odor reflects a mix of these classes.
Thioalcohols: how one potent smell is made
The most striking recent advances concern the thioalcohols, the sulphurous compounds responsible for much of the sharp, oniony note of underarm odor. One of the main ones, 3-methyl-3-sulfanylhexan-1-ol (3M3SH), is so potent that it can be detected at picogram-per-litre concentrations, an order of magnitude lower than many other volatile chemicals.
The apocrine gland does not release 3M3SH directly. Instead it secretes an odorless conjugate that is delivered to the skin surface as a cysteinylglycine dipeptide precursor (S-Cys-Gly-3M3SH). Work by Minhas and colleagues (2018) showed that only a small set of skin bacteria (Staphylococcus hominis, and to a lesser extent S. haemolyticus and S. lugdunensis) carry a dedicated membrane transporter that imports this precursor, after which the bacterium cleaves it to liberate the malodorous 3M3SH. The researchers reported "a strong correlation between S. hominis and body odour production."
This matters because it locates a specific, targetable step in the odor pathway: without bacterial uptake and cleavage of the precursor, the potent thioalcohol is never released.
Everyone's underarm community is a little different
Underarm microbiomes are individual. In the Callewaert (2013) study, samples fell into two broad community types (one dominated by Staphylococcus and one by Corynebacterium) and these were distributed differently by sex: about 87% of the women clustered in the Staphylococcus-dominated type, while roughly 39% of the men clustered in the Corynebacterium-dominated one. Because Corynebacterium is more strongly linked to intense odor, this partly explains reported sex differences in odor character.
The same study found each person's community was largely unique and fairly stable over time, that left and right underarms differed in about half of people, and that more frequent deodorant use was associated with greater bacterial diversity, a reminder that everyday hygiene products reshape the community they act on. These are observational associations from a single cohort, not proof of cause and effect.
What this means in plain terms
Body odor is a collaboration between glands and microbes. The glands supply raw material that has almost no smell; the bacteria, mainly Corynebacterium and specific Staphylococcus species, do the chemistry that produces the smell. That is why odor varies so much between people and body sites, and why it can change when the skin community changes. This page describes the biology only; persistent, distressing, or sudden changes in body odor are worth discussing with a clinician.
Methodology and limitations
This page draws on a peer-reviewed cohort study of the underarm microbiome (Callewaert 2013, n=53), a mechanistic study of thioalcohol production (Minhas 2018, eLife), a biochemistry study of the odor precursor pathway (Martin 2010), and a review of axillary odor microbiology and chemistry (James 2013). Each figure was traced to its source and confirmed on the source page.
Limitations: microbiome composition figures come from a single cohort of 53 adults and will vary with population, sampling method, and sequencing technique. The classification of odor molecules into three classes is a simplification of a larger set of contributing compounds. Sex-based clustering is an observed association, not a deterministic rule. Nothing here is a diagnosis or medical advice.
Frequently asked questions
- Is sweat what actually smells?
- Not on its own. Fresh apocrine underarm secretion is essentially odorless. The smell comes from skin bacteria, mainly Corynebacterium and Staphylococcus species, converting components of that secretion into small volatile molecules (James 2013).
- Which bacteria cause body odor?
- Underarm odor is dominated by two genera: Corynebacterium, the primary driver of intense odor, and Staphylococcus. In one cohort about 77% of underarm bacterial sequences belonged to just these two groups (Callewaert 2013).
- What makes the sharp, onion-like underarm smell?
- Sulphurous thioalcohols such as 3M3SH. Certain Staphylococcus species (notably S. hominis) import an odorless precursor secreted onto the skin and cleave it to release the potent thioalcohol (Minhas 2018).
- Why do men and women sometimes smell different?
- Partly because their underarm communities differ. In one study about 87% of women clustered in a Staphylococcus-dominated community, while more men clustered in a Corynebacterium-dominated one, and Corynebacterium is linked to stronger odor (Callewaert 2013).
- Does deodorant change the underarm microbiome?
- In the Callewaert (2013) cohort, more frequent deodorant use was associated with greater bacterial diversity. This is an observational association from one study, not proof that deodorant use directly causes the change.
- Can body odor ever signal a health problem?
- This page is about normal microbiology. A sudden, persistent, or unusual change in body odor is best discussed with a clinician, who can consider causes beyond the skin microbiome.
Sources
Primary peer-reviewed studies and official sources first, then reviews and institutional framing (secondary).
- Callewaert C, Kerckhof FM, Granitsiotis MS, Van Gele M, Van de Wiele T, Boon N. Characterization of Staphylococcus and Corynebacterium clusters in the human axillary region. PLoS One. 2013;8(8):e70538. Full text
- Minhas GS, Bawdon D, Herman R, Rudden M, Stone AP, James AG, Thomas GH, Newstead S. Structural basis of malodour precursor transport in the human axilla. eLife. 2018;7:e34995. Full text
- James AG, Austin CJ, Cox DS, Taylor D, Calvert R. Microbiological and biochemical origins of human axillary odour. FEMS Microbiol Ecol. 2013;83(3):527–540. PubMed
- Martin A, Saathoff M, Kuhn F, Max H, Terstegen L, Natsch A. A functional ABCC11 allele is essential in the biochemical formation of human axillary odor. J Invest Dermatol. 2010;130(2):529–540. Full text
How to cite this page
Sweat Explained. Body Odor and the Skin Microbiome: The Science. Published 2026-07-13; last reviewed 2026-07-13. Available at: https://sweatexplained.com/research/body-odor-and-the-skin-microbiome
Please cite the original studies for the underlying figures. Journalists are welcome to link to this page; the charts are original renderings of the cited data.