What’s The Chemistry of Smelly Feet?

Few things can clear out a room faster than a bad case of smelly feet. While universally reviled, smelly feet are also extremely common – most people will deal with foot odor at some point in their lives. But what causes feet to smell so bad? The science behind stinky feet reveals that a few key chemical compounds are to blame.

The main culprit behind foot odor is isovaleric acid. This organic acid is produced naturally by bacteria that live on the skin of the feet. These bacteria feast on sweat and particles of dead skin. As they digest these substances, the bacteria release isovaleric acid as a waste product.

Isovaleric acid has a very strong, cheesy type of smell. Even small amounts of isovaleric acid can make feet smell quite potent. The same compound is partly responsible for the smell of certain cheeses like Parmesan. Bacteria on the skin produce even more isovaleric acid in hot weather when feet sweat more profusely.

Another potential source of foot odor is propionic acid. Like isovaleric acid, propionic acid is generated when bacteria on the skin process sweat. However, propionic acid has more of a vinegar-like smell. The smell of propionic acid is most noticeable in cases of hyperhidrosis – excessive sweating of the feet.

In addition, smelly feet frequently result from wearing shoes and socks that are not breathable enough. Feet sweat quite a bit, producing up to half a pint of perspiration per day. If this sweat cannot evaporate, it accumulates in shoes and socks, making an ideal breeding ground for odor-causing bacteria. The dark, moist environment inside shoes promotes bacterial growth and isovaleric acid production.

Going without shoes for too long can also lead to foot odor issues. Regular wear and tear plus contact with dirt and bacteria roughens the skin on the soles and toes. This creates additional surfaces for bacteria to colonize. A buildup of dead skin cells in these areas provides food for the bacteria.

While smelly feet are linked to excess isovaleric acid, propionic acid, and sweat, other factors can make the problem worse. People with hyperhidrosis are more prone to foot odor. The fungal infection athlete’s foot can lead to increased bacteria on the feet. Wearing certain synthetic materials like nylon allows more sweat to accumulate versus natural materials like cotton. Even hormonal changes can increase foot sweating and odor.

The good news is foot odor can usually be controlled with good hygiene. Washing the feet daily with antibacterial soap followed by thorough drying can help decrease bacteria. Changing to moisture-wicking cotton socks and breathable leather or mesh shoes provides less opportunity for sweat buildup. Using antiperspirant or powder on the feet can cut down on sweating. In severe cases, prescription antiperspirants or antibiotics may be used to control excessive foot sweating and odor.

So the next time a suspicious smell fills the room, isovaleric acid produced by sweat-loving foot bacteria may be the culprit. With vigilance and proper foot hygiene, smelly feet can be kept in check. Just be sure to go easy on the Parmesan cheese at dinner.