And for 10% to 15% of people, the smell is really bad. Why? Because their feet are extra sweaty and become home to bacteria called Kyetococcus sedentarius (say: kite-oh-KAH-kus SEH-den-tair-ee-us). These bacteria produce more than just stinky organic acids — they also produce stuff called volatile sulfur compounds. Sulfur compounds usually are powerful and awful smelling. If you've ever smelled a rotten egg, you know what volatile sulfur compounds smell like.