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Why do our feet smell worse in the winter?

Summer is all sweat and exposed toes, so you'd think foot odor would be at its peak in that season. Not so. As the weather turns cooler, feet often turn smellier; at least, that's what anecdotal evidence suggests.

Blame shoes and socks. Enclosing the foot increases heat and traps sweat, said Robert Kornfeld, a doctor of podiatric medicine who runs a holistic and restorative foot and ankle practice in New York.

"If the foot is allowed to [air out] efficiently, you don't build up the breeding ground for bacteria," Kornfeld told Live Science.

Related: Do you really need to buy aluminum-free deodorant?

Stinky feet

Feet on their own don't stink. The real culprits are the bacteria that live on the skin, feeding off the compounds in sweat. A 2006 study in the Canadian Journal of Microbiology found that Staphylococcus epidermidis, a common resident of the skin, creates a compound called isovaleric acid when feeding off an amino acid in sweat called leucine. Isovaleric acid happens to smell rather like pungent cheese.

Another bacteria species, Bacillus subtilis, was also associated with strong odor, the researchers found. These rod-shaped bacteria thrive in the human gastrointestinal tract as well as on the skin.

Depending on the materials you wear, you may be providing these bacteria and others a chance to flourish. Cotton tends to absorb and wick away moisture; synthetic fabrics don't absorb moisture, but instead trap it between fibers. A 2007 study published in the Textile Research Journal found that polyester fabrics are stinkier than cotton or wool. In another study, this one published in 2014, researchers came to the same conclusion after asking subjects to get sweaty by bicycling in either synthetic or natural shirts. Polyester clothing was rated significantly smellier, less pleasant, mustier and more sour than cotton clothing.

Thus, podiatrists tend to give fashion advice to patients who come in complaining of foot stink.

"I tell them to make sure they wear a cotton sock as opposed to a nylon sock," said Rondrick Williamson, a podiatrist in Atlanta. "Cotton is going to breathe a little more."

Defeating the stink

Other steps in preventing foot odor also involve banishing moisture and preventing bacteria from gaining a toehold (sorry). Williamson said he tells his patients to sprinkle shoes with a little anti-fungal powder at the end of each day; this keeps down moisture and prevents nasty infections like athlete's foot, caused by a fungus, from gaining ground. For bad cases, a spritz of Lysol in the shoes can help, too, he said. He also recommended that people with particularly sweaty feet change their socks once or twice during the day, giving bacteria less time to grow.

Kornfeld said he advocates dietary changes, including getting rid of refined sugars, to strengthen the immune system and keep pathogenic bacteria at bay. He also suggested a roll-on antiperspirant applied to the foot. People who are chronically stressed also tend to sweat more, he said, so foot odor is sometimes a sign of a wider systemic issue.

"What's interesting about foot odor is a lot of people are so embarrassed they won't even go to a doctor," Kornfeld said. "But there's help out there."  

Originally published on Live Science.

Stephanie Pappas

Stephanie Pappas is a contributing writer for Live Science covering topics from geoscience to archaeology to the human brain and behavior. A freelancer based in Denver, Colorado, she also regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.