Everybody’s familiar with stinky feet. Most of us have a friend or relative — or maybe it’s you — who can clear out a room when they kick off their shoes.
Even the sweetest-smelling person can do a decent job stinking up a pair of shoes by running a few miles in them. So what’s going on here? Why do your feet have a stronger odor than, say, the palms of your hands, or other parts of your body? After all, isn’t body odor about sweat?
Eau de foot is about sweat, yes. A stinky foot may also be a sweaty foot. Each of your feet has 26 bones, 33 joints, 107 ligaments, and 19 muscles — and as a pair your feet have 250,000 sweat glands that make about one cup (about half a pint) of sweat every day. That means your feet produce more sweat per square inch of skin than any other part of your body. But most of the time sweat itself actually isn’t the problem, at least not when it comes to the kind of sweat you find on your feet. You see, there are two types of sweat glands on your body: apocrine glands and eccrine glands.
Apocrine glands are found near hair follicles (so you’ll find them in abundance on your scalp and in your armpits, as well as the groin region). The sweat they secrete — a yellowish, thick fluid — happens in response to stresses. Body odor is the byproduct of bacteria on your skin digesting the sweat produced by apocrine glands. But there are no apocrine glands on your feet.
Eccrine glands, on the other hand, are located in the skin all over your body, including your feet. This sweat is intended to cool you down. On its own, the sweat produced by the eccrine glands on the soles of your feet is pretty much just water and salt, and really doesn’t have any odor at all.
It’s bacteria that’s the real culprit behind foot odor; well, that and whether or not you wear socks.
The Bacteria Behind Foot Odor
Staphylococcus epidermidis and Bacillus subtilis, for example, are two types of bacteria that naturally live on the skin of your feet. Yes, they like living in the moist, warm environment your sock provides, but they also like life on a sweaty bare foot — and they really like to eat an amino acid, leucine, found in the sweat the eccrine glands in your feet produce. When these bacteria eat leucine they produce their own gassy byproduct: isovaleric acid. This isovaleric acid is what gives both stinky cheese and stinky feet their malodorous scent. Foot odor can be particularly pungent if you happen to be a person who has a lot of B. subtilis living on your feet; as it turns out, they’re naturally a bit stinkier (with a hint of vinegar) than other bacteria living off your leucine.
Different bacteria produce different odors, though, and if your feet tend to have a sulfuric or ammonia-like aroma, you can blame a different microorganism: Meet Brevibacterium linens.
B. linens is the bacteria that gives the notoriously stinky Limburger cheese its odor, and it’s also the culprit behind most foot odor.B. linens flourish in environments that are salty, and that are about 70 to 85 degrees Fahrenheit (20 to 30 degrees Celsius). Sound a bit, perhaps, like a sweaty foot? It’s pretty close, but while B. linens like this climate, they don’t really care so much about your sweat. B. linens like to eat the dry, dead skin cells on the soles of your feet — they don’t care if your soles are sweaty or not — and as they digest your skin they produce rotten-egg odors (sulfur), a byproduct that happens as they convert amino acids in your skin into methanethiol.
