Are you training for a marathon, or do you just like to run? Either way, here’s the solution to a known problem.

You know the drill: You’re feeling sporty, you go for a run, and you come home sweaty and feeling great. Sure, you got your pulse up in the meantime, but now you’re left with a nasty smell in your sneakers. How did that happen?

The culprit is bacteria. In fact, the same bacteria that make your armpits smelly are also making your running shoes stink. Our feet and hands are covered with sweat glands, but while sweat can evaporate from your hands, it gets trapped in our socks and shoes.

“Just as with all other organisms, bacteria needs 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 staphylococcus, micrococcus 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.

“I don’t worry that my running shoes smell because, luckily, there’s something you can do to fix that,” says Landvik.

Three steps to fresher running shoes
Freeze: Put your shoes in the freezer to kill the bacteria, as they cannot endure cold temperatures.
Dry: Microorganisms thrive in damp conditions, so keep your shoes dry, for example, by stuffing them with newspaper after a run.
Neutralize: Because the smell in your shoes comes from isovaleric acid, you can neutralize it with an alkaloid like baking soda. Sprinkle half to a whole tablespoon of plain baking soda into each shoe and leave them overnight.

What are bacteria?
Bacteria are microscopic single-celled organisms. They were among the first life forms to appear on Earth and are practically present everywhere. They inhabit soil and water and live in symbiotic relationships with humans, plants and animals. Bacteria are extremely important in ecosystems, where they are crucial to maintaining life and breaking down materials such as plants.

Bacteria can do much more than make your shoes smell. Companies like Novozymes utilize bacteria for their many benefits. For example, bacteria and other types of microbes are used as natural fertilizers in agriculture. Microbial solutions protect crops against diseases and help plants grow better.