Why Feet Smell: The Actual Chemistry

6 min read science

That's the whole thing in four sentences. Below is where each piece comes from, including the part where the research admits it hasn't measured the most interesting spot.

I want to be upfront about something. I sell socks, so I have an obvious interest in you believing a particular story about your feet. The defence against that is citations you can check, so everything on this page is attributed and most of it is one click from the abstract.

Sweat has no smell

Start here, because it reframes everything else.

Eccrine sweat is mostly water with salts and a small amount of organic material, including amino acids. It comes off your skin with essentially no odour. If you could sweat into a sterile container you would have a faintly salty liquid and nothing else.

Your feet produce a lot of it. Eccrine glands are distributed across the body but not evenly, and according to StatPearls, the clinical reference on the NCBI Bookshelf, they sit "throughout the body, most numerously on the soles of the feet."

So: the highest concentration of sweat glands you own, producing a liquid that doesn't smell.

Something else has to happen.

The reaction, specifically

What happens is bacterial metabolism.

Bacteria on your skin take the amino acid L-leucine from your sweat and convert it into isovaleric acid, a short-chain fatty acid with a distinctive cheesy smell. That's the reaction. Foot odour is, chemically, mostly that one compound and a few relatives.

Kanda and colleagues documented the process in the Canadian Journal of Microbiology in 2005, in a paper titled "Foot odor due to microbial metabolism and its control" (PMID 16699586).

The finding has held up and been sharpened since. A 2026 paper in the Journal of Applied Microbiology by Sakai and colleagues isolated the organisms from Japanese subjects with foot malodour and confirmed the same conversion of L-leucine to isovaleric acid (DOI 10.1093/jambio/lxag121).

Two things follow from this that most foot odour advice gets backwards.

The smell is produced, not released. It isn't sitting in your sweat waiting to escape. It's manufactured, on your skin, over hours, by something alive.

And the raw material is a normal component of normal sweat. There is nothing wrong with your sweat. There is nothing unusual about you having amino acids in it.

Which bacteria

The 2026 paper named two: Kytococcus schroeteri and Staphylococcus hominis.

That second one matters more than it sounds. Staphylococcus is not an infection or an invader here. It's ordinary resident skin flora, present on essentially everyone.

A 2015 study in FEMS Microbiology Ecology by Stevens and colleagues sampled eight sites across the foot and found that Staphylococcus species "were dominant across different foot sites and comprised almost the entire bacterial population on the plantar surface" (DOI 10.1093/femsec/fiu018).

Almost the entire population. On the sole.

So the organisms responsible are the ones that live on everybody's feet all the time. This is worth sitting with if you have ever concluded that your feet smell because there is something wrong with you specifically. The cast is the same on everyone. What differs is the conditions.

Why the sole and not the top of your foot

The Stevens study produced one result I think about a lot.

They sampled dorsal sites, on the top of the foot, and plantar sites, on the sole. Then they measured the volatiles.

Their finding: "isovaleric acid was not detected on the dorsal surface but was present on the plantar surface," which they attribute to the high numbers of Staphylococcus residing there.

Same foot. Same person. Same day. Two centimetres apart, and one surface is producing the compound while the other isn't.

That tells you the variable isn't your body. It's local conditions: which skin is enclosed, which skin is damp, which skin has air moving across it.

The part the research hasn't measured

Here's where I have to be careful, because this is the bit my product is about and I'd rather you heard the limitation from me.

The Stevens paper includes this line: "The inter-toe web space is reported to sustain the highest microbial populations on the foot; however, due to the absence of a suitable sampling method...this site was not evaluated in the present study."

Read that twice.

The space between your toes is reported to have the highest microbial population anywhere on the foot. And they could not sample it, because there wasn't a good method for getting at a surface that is pressed flat against another surface.

So the place with the most bacteria is the place that is hardest to measure, for exactly the same reason it has the most bacteria: two skin surfaces in contact, no air, nothing gets in there. Not a swab, not a spray, not a powder.

I think that's the single most useful fact on this page, and I'm not going to overstate it. It is a statement about sampling difficulty and a reported population, not a controlled comparison of toe web versus sole. If someone runs that study properly I'll link it here, whichever way it comes out.

What actually controls it: airflow

If the bacteria are a constant, the conditions are the lever.

A 2021 study in Scientific Reports by Miao and colleagues measured the microclimate inside shoes and matched it against bacterial growth on plantar skin (DOI 10.1038/s41598-021-99865-x). In-shoe temperatures ran between 27 and 37 °C.

Their result: bacterial growth at the distal plantar skin "showed a positive linear correlation with the in-shoe temperature and absolute humidity, and a negative linear correlation with the ventilation rate."

And their conclusion about which factor to watch: "ventilation rate seemed to be a more reliable indicator of bacterial growth."

Ventilation. Not heat, not humidity, not hygiene. How much air is moving.

That single sentence explains why perforated shoes beat closed ones, why sitting at a desk all day is worse than walking, and why the most enclosed space on your foot is the one with the most bacteria living in it.

Why washing doesn't hold

Not because washing is useless. Because it isn't durable.

You wash, you dry, you put a sock on and close a shoe around it. Within minutes the inside of that shoe is warm and humid again, and the resident flora, which was never fully removed and shouldn't be, starts back up with fresh sweat and fresh leucine.

The reaction doesn't need long. It needs the conditions, and you rebuilt them when you tied your laces.

Keep washing. Just stop treating it as the thing that failed, because it was never the variable that was going to hold.

Sources: Kanda F, et al. "Foot odor due to microbial metabolism and its control." Canadian Journal of Microbiology, PMID 16699586. Sakai M, Mori I, Kawasaki A, Takigawa H, Kinoshita K, Aosaki T, Sakasai M, Sugai Y. "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. "Spatial variations in the microbial community structure and diversity of the human foot is associated with the production of odorous volatiles." FEMS Microbiology Ecology 91(1), 2015, DOI 10.1093/femsec/fiu018. Miao T, Wang P, Zhang N, Li Y. "Footwear microclimate and its effects on the microbial community of the plantar skin." Scientific Reports, 2021, DOI 10.1038/s41598-021-99865-x. "Anatomy, Skin Sweat Glands," StatPearls, NCBI Bookshelf.

Related: Why your feet sweat more in leather shoes · Toe socks with dress shoes: a complete guide · Foot odor at the office

Common questions

Does sweat itself smell?
No. Eccrine sweat is largely water and salts and comes off the skin essentially odourless. The smell is produced afterwards by bacteria converting amino acids in it.
What chemical makes feet smell?
Mainly isovaleric acid, a short-chain fatty acid produced when skin bacteria convert the amino acid L-leucine. Kanda et al. documented this in the Canadian Journal of Microbiology in 2005.
Which bacteria cause foot odour?
A 2026 paper in the Journal of Applied Microbiology isolated Kytococcus schroeteri and Staphylococcus hominis. These are ordinary resident skin bacteria rather than an infection.
Why do my feet smell when other people's don't?
The bacteria are common to nearly everyone. What differs is conditions: enclosure, moisture and airflow inside your footwear, rather than anything unusual about your skin.
Does killing the bacteria fix it?
The resident flora on your skin returns, and removing it entirely isn't a goal worth having. Research points at conditions rather than eradication: the 2021 Scientific Reports study found ventilation rate to be the more reliable indicator of bacterial growth.
Do plant extracts work against foot odour?
The 2026 Sakai paper found that extracts of Sanguisorba officinalis and Eucalyptus globulus inhibited generation of isovaleric acid from L-leucine in their testing. That's a laboratory result on the reaction, not a finished consumer product, and it isn't something we use.