We’ve all caught a whiff of someone’s smelly feet before. While it may be unpleasant, smelly feet are very common. But what causes that noxious foot odor in the first place? As it turns out, there are a few key chemicals and biological processes that contribute to making feet stink.
Sweat itself is odorless. The main culprit behind smelly feet is bacteria. Our feet contain more sweat glands per square inch than any other part of our body. When your feet sweat, that moisture gets trapped inside your shoes, creating an ideal environment for bacteria to thrive. There are over 250,000 sweat glands in each foot, producing nearly a pint of sweat per day. When the sweat mixes with dead skin cells and bacteria, the chemistry taking place produces the telltale odor we recognize as stinky feet.
One of the most common bacteria found on our skin and responsible for foot odor is Bacillus subtilis. This hardy bacteria produces acidic byproducts as it breaks down the proteins and salts found in sweat. These byproducts include chemicals like isovaleric acid and butyric acid. Have you ever noticed the same cheesy, vinegary type of smell coming from both feet and certain aged cheeses? That’s because the same acids produced by the bacteria Brevibacterium are found in each—its the acids that create that distinctive scent.
Another type of bacteria frequently found on the skin of sweaty feet is Staphylococcus epidermidis. This microbe generates even more types of smelly organic acids including isoletic acid, propionic acid, and acetic acid. Because these naturally occurring acids have very low pH levels and potent odors, they vaporize easily. When pressure is applied inside shoes, gases get released and the acids can spread, making feet smell even worse.
Meanwhile, yeast and fungi thrive by feeding on dead skin cells. A common type of fungus connected to foot odor is Trichophyton rubrum. Dermatophytes like these contain specialized enzymes to dissolve keratin—the key protein that makes up skin, hair, and nails. The byproducts of this digestion accumulate and contribute to the overall stench coming from feet. Yeast-related foot infections like athlete’s foot can make odors even more pronounced.
The main components of foot sweat itself are water, minerals like potassium and sodium chloride, fats, proteins, and waste products including urea, uric acid, and ammonia. Ammonia is actually odorless, but certain bacteria will break it down into chemicals like pyridine and putrescine, both of which have very strong, unpleasant smells associated with decaying tissue.
When all these smelly organic acids, sulfur compounds, fatty acids, and products of skin cell decay accumulate, they produce what is perceived as unpleasant foot odor. Odor intensity can range from mild cheese-like smells to putrid garbage scents if certain bacteria and fungi populations are allowed to grow unchecked.
In addition to bacteria and fungi populations on the skin, there are a few other factors that can make feet more likely to smell:
Excessive Sweating: Those with hyperhidrosis produce much more sweat, providing extra food for microbes. This can worsen foot odor.
Wearing Closed Shoes and Tight Hosiery: Trapping sweat and bacteria promotes their multiplying numbers.
Poor Foot Hygiene: Infrequent cleaning gives bacteria and fungi more time to grow and generate smelly metabolic waste.
Genetics: The microbiome of the skin naturally varies person to person. Some people simply harbor more odor-causing microbes.
Diet and Lifestyle: Consumption of strong foods containing garlic, onions, curry, or caffeine can lead to those scents manifesting when sweat breaks particular compounds down. Smoking can also intensify foot odor.
Of course, prevention is key when it comes to keeping foot odor at bay. Letting your feet air out when possible can help. Washing feet daily with antibacterial soap, exfoliating to remove dead skin cell buildup, wearing moisture wicking socks, using foot powders and deodorants, and frequently changing into clean shoes can all help combat smelly feet. Seeing a doctor to address excessive sweating or possible fungal infections may also be warranted.
The microbes naturally living all over our bodies serve important protective roles, but when allowed to overpopulate in warm, moist environments like our feet inside shoes, their metabolic byproducts and waste generates some less-than-pleasant smells. But understanding what’s behind foot odor can help develop better strategies to keep our feet fresh. With vigilance about foot hygiene and antibacterial intervention when needed, smelly feet don’t have to be an embarrassing inevitability.
