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Did you know that sweat itself doesn’t smell? The odor you find in your running shoes actually comes from bacteria: It comes out in the chemical process of bacteria on your skin breaking down acids in your sweat. Though the sweat glands in your arm pits vary from those in your feet, the process of breaking down acids is the same and can also leave behind an odor.
Along with the palms of the hands, the soles of the feet contain the greatest concentration of sweat glands with each foot containing 600 to 700 per square centimeter. In total, the human body has between 1.6 to 5 million sweat glands.
So it’s no wonder when all that sweat and bacteria get trapped in our running shoes and socks that our shoes would retain the smell after going unwashed day after day. On the other hand, our feet and socks get washed and disinfected regularly.
“Just as with all other organisms, bacteria need fluid to thrive, and your foot sweat does that job perfectly,” explains Sara Landvik, who works at Novozymes and is an expert in bacteria and other microorganisms.
Our skin is covered with bacteria, including staphylococci, micrococci, and corynebacterium—and that’s quite normal. When your feet sweat, corynebacterium and micrococci break down the sweat into a fatty acid called isovaleric acid, which causes the smell in your running shoes.
But bacteria can do much more than make your shoes smell—they can do good things, too. They are extremely important in ecosystems, where they are crucial to maintaining life and breaking down materials such as plants. Today, bacteria are used as a natural fertilizer in agriculture, for the production of flowers, vegetables, and crops such as soy. Microbial solutions protect crops against diseases and help plants grow better.
Deodorant companies have even started selling probiotic deodorants as a way of promoting the growth of good bacteria that don’t stink while thwarting the malodorous ones. (Though, the research behind this kind of microbiome magic is still in the early stages.)
And while we have a host of products and tactics to keep our pit odor under control, many of us don’t pay near enough attention to our feet. Here are 5 ways to keep the bacteria in your running shoes under control.
How to Get Smell and Bacteria Out of Shoes (And Keep It Out)
Deodorizing shoes is not just important for the social factor of not being the person with smelly shoes, but it is also a practice in foot health. Remember, smell comes from the combination of bacteria and sweat. According to this article in the Journal of Athletic Training, athletes are more susceptible to bacterial and fungal infections on their feet. And while bacteria-rich shoes are not the only cause of infections like athlete’s foot, giving them some TLC is just one more way to keep feet healthy.
1. Freeze them.
Although it’s been disproven that freezing textiles kills all bacteria, it does kill some. Put your shoes in the freezer to reduce the amount of bacteria and some odor. If you choose to go with this method, however, we recommend putting your shoes in some sort of plastic bin, container, or plastic bag to prevent your shoes from coming out smelling like frozen taco meat (and to keep your frozen taco meat from smelling like feet). That goes for any other foot product you store in your freezer, like yogatoes or special ice packs.
2. Keep them dry.
Bacteria and microorganisms thrive in damp conditions, so keep your shoes dry, for example, by stuffing them with newspaper after a run. Storing shoes out in the sun has also been proven to be an effective method of drying and sanitizing footwear.
3. Rotate which shoes you wear.
If you’re able to invest in more than one pair at a time, try not to run in the same pair of shoes two days in a row. Giving your shoes at least 24 hours to dry out will prevent any scents from lingering.
4. Neutralize the odor.
Because the smell in your shoes comes from isovaleric acid, you can neutralize it with an alkaline compound like baking soda. Sprinkle half to a whole tablespoon of plain baking soda into each shoe and leave them overnight. Or opt for a product designed to neutralize odors in shoes specifically. “Silica gel sachets can be kept in the shoe during storage and baking soda breathable pouches can also be kept inside to avoid smell,” says Preeti Arya, assistant professor of textile development and marketing at the Fashion Institute of Technology.
5. Wash them.
Running shoes can and should be washed at least once in their lifecycle. Arya recommends washing running shoes once every two months. The brand website for the specific pair of shoes that you run in will provide the best advice for washing that pair without damaging them (such as hand washing versus machine washing).
These methods should work wonders on the everyday sweat that runners build up, but if you have issues with chronic sweating (such as hyperhidrosis) or deal with fungal infections regularly, you may want to speak with a specialist.