Smelly shoes are an all-too-common issue. It can be annoying; no matter how clean your feet are, they still end up making your sneakers smell. At worst, it can be downright unpleasant, forcing you to ask, “How can I remove the smell from my shoes?”

Bacteria are the culprit of stinky shoes. They grow in large numbers on your feet, producing organic acids — methanethiol, isovaleric acid, and propanoic acid — as waste products. While these types of bacteria aren’t harmful, they can leave a lingering stink.

For example, methanethiol is produced as a byproduct of Brevibacterium, the primary bacteria found on the feet. This organic acid has a distinct sulfuric stench that resembles rotting cabbages and smelly socks.

Even with the best foot hygiene, your feet may still smell. That's partly because your feet contain more sweat glands per square inch than anywhere else on your body. While sweat itself doesn’t smell, those bacterial waste products do. This makes shoes an ideal breeding ground for bacteria, because they trap sweat and moisture, creating an environment for bacteria to thrive.