Which Bacteria Cause Foot Odor?

5 min read science

That last sentence is the reason most people run this search, so it goes near the top.

If you're here because something on your foot hurts, is broken, is changing colour, or is spreading, close this page and see a clinician. I make socks. Everything below is about the normal situation where healthy skin produces a smell.

The named organisms

Four species have been isolated by name in peer-reviewed work on foot odour specifically.

Staphylococcus epidermidis. The main one. Ara and colleagues, writing in the Canadian Journal of Microbiology in 2006, describe isovaleric acid as being "produced when Staphylococcus epidermidis, a resident species of the normal cutaneous microbial flora, degrades leucine present in sweat" (PMID 16699586).

Read that phrasing carefully: a resident species of the normal cutaneous microbial flora. The organism doing most of the work is one that belongs there.

Bacillus subtilis. Also identified in the same study, associated with intensified odour rather than with the base reaction.

Kytococcus schroeteri and Staphylococcus hominis. Isolated twenty years later by Sakai and colleagues in the Journal of Applied Microbiology, from Japanese subjects with foot malodour, performing the same conversion of L-leucine into isovaleric acid (DOI 10.1093/jambio/lxag121).

Two studies, two decades apart, different populations, same chemistry. Different organisms can run the same reaction, which is part of why this problem is so stubborn. It isn't one bug you can target.

More broadly, a 2015 survey in FEMS Microbiology Ecology found Staphylococcus making up nearly the whole bacterial population of the sole (DOI 10.1093/femsec/fiu018).

Nearly the whole population. The genus doing this is also the genus that lives there normally, in enormous numbers, on everyone.

No, it isn't an infection

I want to be direct about this because it's the unspoken worry behind the search.

An infection involves an organism that doesn't belong, or a normal organism in a place or quantity that causes damage. What the foot odour literature describes is different: normal resident flora, in normal quantities, doing normal metabolism, on intact skin.

The smell is a byproduct of ordinary skin ecology meeting an unusual environment. It isn't a sign that your skin has been colonised by something foreign.

The research language reflects this. Ara's paper doesn't describe eradicating a pathogen; it describes controlling a metabolic reaction. Nobody in this field is treating a disease.

Again, with the caveat above: pain, broken skin, discolouration or spreading changes are a different category and belong with a clinician.

Where they live on your foot

The 2015 FEMS study sampled eight sites across each foot, four on top and four on the sole, and the populations turned out not to be evenly spread.

The sole was dominated by Staphylococcus almost to the exclusion of everything else. The top of the foot carried far more diversity. The volatile measurements tracked the bacteria: the odour compound showed up on the sole and not on the top of the same foot.

The same paper flags that it could not sample the space between the toes at all, which is where the densest population is reported to be. I've written about what that does and doesn't prove, including the part where it proves less than I'd like, in the chemistry piece.

Should you try to kill them?

The instinct is obvious and the answer is more interesting than yes or no.

You can reduce skin flora temporarily. You cannot sterilise skin, and the population re-establishes. That's what resident flora means.

More telling is what the researchers themselves went looking for. Ara's 2006 team screened compounds for the ability to stop the smell, and what they reported finding were three, citral and citronellal and geraniol, that "inhibit the generation of isovaleric acid at low concentrations" while, in the study's framing, avoiding disruption of the normal skin microbiota.

That's worth dwelling on. Given the option, the people studying this did not set out to wipe out the bacteria. They went looking for something that would interrupt the reaction and leave the ecosystem intact.

The 2026 study took the same shape, testing botanical extracts of Sanguisorba officinalis and Eucalyptus globulus for inhibition of isovaleric acid generation from L-leucine. Again: interrupt the reaction, don't sterilise the skin.

Neither of those is a consumer product recommendation, and neither is anything we use. I'm describing what the field does, not selling you an extract.

What the research targets instead

Conditions.

A 2021 study in Scientific Reports measured the microclimate inside shoes against bacterial growth on plantar skin and found growth correlated positively with in-shoe temperature and humidity and negatively with ventilation rate, concluding that "ventilation rate seemed to be a more reliable indicator of bacterial growth" (DOI 10.1038/s41598-021-99865-x).

Same bacteria, everywhere, on everyone. What varies is how warm, how wet, and how still the air is where they're living.

Which is a more useful thing to be able to change than your own skin flora, and considerably easier.

Sources: Ara K, Hama M, Akiba S, Koike K, Okisaka K, Hagura T, Kamiya T, Tomita F. "Foot odor due to microbial metabolism and its control." Canadian Journal of Microbiology 52(4):357-64, 2006, PMID 16699586. Sakai M, et al. "Kytococcal and staphylococcal strains isolated from Japanese subjects with foot malodor and their control." Journal of Applied Microbiology 137(6), 2026, DOI 10.1093/jambio/lxag121. Stevens D, et al. FEMS Microbiology Ecology 91(1), 2015, DOI 10.1093/femsec/fiu018. Miao T, et al. Scientific Reports, 2021, DOI 10.1038/s41598-021-99865-x.

Related: Why feet smell: the actual chemistry · Sweat is odorless · Why your feet sweat more in leather shoes

Common questions

What bacteria make feet smell?
Staphylococcus epidermidis is the principal one identified, with Bacillus subtilis linked to intensified odour (Ara et al., 2006). A 2026 study also isolated Kytococcus schroeteri and Staphylococcus hominis.
Is foot odour caused by an infection?
The organisms named in the research are normal resident skin flora rather than pathogens. Pain, broken skin, discolouration or spreading changes are a separate matter and warrant a clinician.
Can you get rid of the bacteria that cause foot odour?
Not permanently. Resident skin flora re-establishes after washing. Research has focused on inhibiting the odour-producing reaction rather than removing the organisms.
Why do the same bacteria smell on my feet and not my hands?
Conditions. Your hands are ventilated, dry quickly and aren't enclosed for nine hours. The 2015 FEMS study found isovaleric acid on the sole of a foot but not on the top of the same foot, which is the same principle at a smaller scale.
Do antibacterial socks work?
That depends entirely on what a given product does and what evidence it publishes, and it isn't something I can answer generically. What the literature points at most consistently is ventilation and moisture rather than antibacterial action.