Cheese and feet smell alike because they share the same bacteria. A microorganism called Brevibacterium linens thrives both on the surface of washed-rind cheeses and on human skin, particularly between the toes. In both places, it feeds on proteins, breaks down amino acids, and releases the same pungent chemical byproducts. The overlap isn’t a coincidence or a vague similarity. It’s the same biological process happening in two different locations.
The Bacterium Behind Both Smells
Brevibacterium linens belongs to a family of bacteria called coryneforms. On your feet, it feeds on dead skin cells in the warm, moist spaces between your toes. On cheese, it colonizes the damp, salty rind during aging. In both environments, it does the same thing: it breaks down amino acids and spits out sulfur-containing compounds that your nose detects as funk.
Two amino acids drive most of the smell. When the bacteria break down methionine, they produce methanethiol, a gas that smells like rotten cabbage and has an extraordinarily low odor threshold. Humans can detect it at concentrations as low as 0.0005 parts per million, which means even tiny amounts register as powerfully unpleasant. When the bacteria break down leucine, the end product is isovaleric acid, a compound officially described in chemical databases as having a “disagreeable, rancid, cheese-like odour.” That description is circular for a reason: isovaleric acid is one of the defining scent molecules of both strong cheese and sweaty feet.
How Cheese Makers Encourage These Bacteria
Not all cheeses smell like feet. The ones that do are typically washed-rind varieties, where the cheesemaker deliberately creates conditions that favor Brevibacterium linens growth. During aging, the surface of the cheese is periodically washed with a brine solution, sometimes mixed with beer, wine, or spirits. This process, called smearing, keeps the rind moist, restricts mold growth, and creates a salty, humid environment that these bacteria love.
The microbial succession on a washed-rind cheese is surprisingly orderly. First, yeasts colonize the surface and lower the acidity. That shift in pH opens the door for coryneform bacteria like Brevibacterium linens to take hold. As the bacteria multiply, they produce sulfur compounds, ammonia, and hydrogen sulfide, all of which contribute to the cheese’s intense aroma. They also produce carotenoid pigments, which is why the rind of these cheeses turns reddish-orange.
Limburger is the classic example, notorious enough that its name has become shorthand for stinky cheese. But the same bacterial ripening process happens in Epoisses, Münster, Taleggio, Brick, Appenzeller, and Trappist-style cheeses. Methanethiol is even a natural volatile component of Beaufort, a Gruyère-type cheese from the French Alps.
Why Leucine Creates That Specific Funk
The conversion of leucine to isovaleric acid follows a two-step process. First, bacteria strip the amino group from leucine through a reaction called transamination, producing an intermediate compound. Then enzymes convert that intermediate into isovaleric acid, the dominant end product regardless of conditions. Related amino acids like isoleucine and valine go through the same type of breakdown, producing their own branched-chain fatty acids that add layers to the overall smell profile of aged cheese.
Isovaleric acid is so strongly associated with cheese flavor that it’s actually used as a food additive in small amounts: around 14 parts per million in ice cream, 12 in candy, and 2.4 in processed cheese products. At low concentrations it reads as tangy and complex. At higher concentrations, or when you’re told you’re smelling feet, it becomes repulsive.
Your Brain Decides Whether It’s Delicious or Disgusting
Here’s the most fascinating part: the same molecule can smell appetizing or revolting depending entirely on what you think you’re smelling. Researchers at Oxford demonstrated this by having people sniff isovaleric acid mixed with cheddar cheese flavoring. When participants were shown the label “cheddar cheese,” they rated the smell as significantly more pleasant than when the exact same odor was labeled “body odor.” Brain imaging showed that the label changed activity in regions involved in emotional processing and reward. The cheese label activated pleasure-related areas more strongly, while the body odor label suppressed them.
This means the overlap between cheese and feet isn’t just a fun fact. It reveals something real about how smell works. Your nose detects the same molecules either way. It’s your brain, armed with context, that decides whether you’re experiencing something appetizing or something you want to get away from. A wedge of Époisses on a cheese board and a pair of gym socks after a long run are, at the molecular level, broadcasting remarkably similar signals. The difference is entirely in your head.
Not All “Stinky” Cheeses Use the Same Bacteria
While Brevibacterium linens gets most of the attention, the surface of a washed-rind cheese is a complex ecosystem. Researchers have identified that dairy strains and skin strains of Brevibacterium are actually distinct species. The cheese isolates were classified as Brevibacterium casei, while those from human skin were named Brevibacterium epidermidis. They’re close relatives doing similar metabolic work, but they’re not genetically identical. Other bacteria on the cheese surface, including Corynebacterium, Arthrobacter, and Staphylococcus species, also contribute sulfur compounds and other volatile molecules to the overall aroma.
On your feet, the same family of coryneform bacteria works alongside Staphylococcus epidermidis. Together, they convert methionine into methanethiol and leucine into isovaleric acid. The warm, enclosed, slightly damp environment inside a shoe is, from a bacterium’s perspective, not so different from a cheese cave: a protein-rich surface, consistent moisture, and limited competition from other organisms. Both environments select for the same types of microbes, which produce the same smelly outputs. That’s why the resemblance is so uncanny.