What causes foot odour?

Sweat is odourless. Staphylococcus epidermidis, which lives naturally on the skin, breaks down the amino acid leucine in sweat and produces isovaleric acid; this acid is the main component of foot odour.

How do you use Air Biotics on shoes?

Spray inside the shoes and onto the inner lining of your gym bag, and let it dry before wearing.

Shoes · 4 min read · 3 October 2026

What causes smelly shoes?

Sweat has no smell. We explain what produces the odour inside your shoes and how to reduce it.

C₅H₁₀O₂Isovaleric acid

In short

1The main component of foot odour is isovaleric acid.
2Bacteria living on the skin produce this acid by breaking down an amino acid in sweat.
3Letting shoes dry out is the most important thing for reducing the smell.

Sweat doesn't smell, bacteria do

The soles of the feet have the densest concentration of sweat glands in the body. Sweat itself is odourless. A study in Japan showed that the main component of foot odour is isovaleric acid. It is produced by Staphylococcus epidermidis, which lives naturally on the skin, when it breaks down the amino acid leucine in sweat.

A closed shoe is warm and humid. Bacteria multiply there, and the shoe's inner lining holds on to the smell. Even after the shoe comes off, production continues until the fabric dries.

Same with your gym bag

Leave a wet towel, worn socks and training kit in a closed bag overnight and the same process happens there too.

What can you do?

The aim is to keep the inside of the shoe dry and not give sweat-feeding bacteria a favourable environment.

01Don't wear the same shoes two days in a row; give them a day's rest.
02When you take your shoes off, remove the insoles and dry them in the open air.
03Apply a probiotic spray inside and let it dry before wearing.
04Empty your gym bag when you get home; don't leave wet things sitting in it.

Questions

What causes foot odour?: Sweat is odourless. Staphylococcus epidermidis, which lives naturally on the skin, breaks down the amino acid leucine in sweat and produces isovaleric acid; this acid is the main component of foot odour.
How do you use Air Biotics on shoes?: Spray inside the shoes and onto the inner lining of your gym bag, and let it dry before wearing.

Sources

All literature →

01
Foot odor due to microbial metabolism and its control
Ara K, Hama M, Akiba S et al. (2006). Canadian Journal of Microbiology 52(4): 357-364
doi:10.1139/w05-130
Finding · Laboratory studyThe main component of foot odour is isovaleric acid. Staphylococcus epidermidis, found naturally on the skin, produces this acid by breaking down the amino acid leucine in sweat.

These studies were not carried out with Air Biotics. What we say about the product is limited to what is written on its packaging; Air Biotics is not a disinfectant.

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