We’ve all caught a whiff of them before – those nauseatingly pungent feet that assault your nostrils and make your stomach churn. Stinky feet have an unmistakable funk that once smelled, is never forgotten. So what causes feet to reek so badly and what exactly does that stench consist of?
Stinky feet are typically the result of wearing tight, non-breathable shoes and socks that create a hot, sweaty environment where bacteria thrive. Feet alone don’t usually smell bad. In fact, sweat itself is virtually odorless. The funk arises when the sweat on our feet mixes with bacteria, causing a chemical reaction that produces foot odor.
Our feet contain over 250,000 sweat glands and on average, produce a pint of sweat per day. When feet are confined in shoes and socks all day, that sweat doesn’t have a chance to evaporate. Damp, dark environments allow bacteria to rapidly multiply. Two of the biggest offenders are Staphylococcus and Corynebacterium species. As the bacteria feast on the dead skin cells and oils on our feet, they release waste products called volatile organic compounds. These are what give stinky feet their eye-watering smell.
Other factors can also contribute to extra smelly feet like hyperhidrosis (excessive sweating), fungal infections like athlete’s foot, wearing the same shoes over and over, poor hygiene, open wounds or blisters, and certain medications and diseases like diabetes that can increase sweating.
The Main Culprits
When it comes to the science behind stinky feet, there are two main chemicals responsible for that noxious odor:
Isovaleric Acid – This smelly substance is produced by Staphylococcus bacteria eating away at your sweat. Studies show that isovaleric acid is found in unusually high concentrations on the feet of people with foot odor issues. It gives off a funky, cheesy scent reminiscent of sweaty socks.
Methanethiol – This sulfur compound is released as a byproduct when Corynebacterium feed on fatty acids and skin cells between the toes. Methanethiol is known for its potent “rotten egg” odor and is a major contributor to stinky feet. Even the smallest amounts can be detected due to its extremely low odor threshold.
Other volatile organic compounds like propionic acid, butyric acid, and acetic acid are also associated with foot odor, though isovaleric and methanethiol are the primary culprits.
Describing the Stench
So how best to describe the unique stench of particularly pungent feet? Smelly feet harbor an assaulting funk that permeates the air and cannot be ignored. Here are some of the most common descriptions of how stinky feet smell:
- Like moldy cheese – The isovaleric acid gives sweaty feet a rancid, cheesy quality. Feet sometimes even smell like parmesan cheese that’s been left out too long.
- Rotten eggs/sulphur – Methanethiol is responsible for those unpleasant rotten egg and sulphur notes. This odor really hits the nose.
- Vinegar/acetone – Notes of vinegar or acetone can come through. Vinegar is produced by acetic acid built up on the feet.
- Corn chips/Fritos – Stinky feet often have a musty, corn chip-like smell similar to Fritos. Propionic acid is the source of this scent.
- Locker room funk – The overall sweaty, bacterial aroma of unwashed feet is reminiscent of a high school locker room. An unpleasant musk that you can almost taste.
- Dead fish – In severe cases, the smell of feet can mirror that of old, stale fish. The concept of foot “freshness” no longer applies.
- Burning rubber – Putrid foot odor also can take on a hot, burning rubber scent. This likely comes from methanthiol.
- General body odor – Stinky feet produce a strong body odor smell mixed with sweat that’s hard to pin down. The overall stench is just foul and dirty.
- Barnyard – Offensive feet sometimes even emit farm-like smells like cows, horses, and manure. Powerfully unpleasant.
So in summary, stinky feet generate a complex funk that can’t be tied to just one aroma. Notes of cheese, eggs, vinegar, corn chips, locker rooms, and burning rubber all blend together to create that universally pungent foot smell we all dread. If you detect any of those scents, odds are there are some stinky feet in the vicinity.