The distinctive odor of feces is due to bacterial action. Gut flora produce compounds such as indole, skatole, and thiols (sulfur-containing compounds), as well as the inorganic gas hydrogen sulfide. These are the same compounds that are responsible for the odor of flatulence. Consumption of foods prepared with spices may result in the spices being undigested and adding to the odor of feces.

The perceived bad odor of feces has been hypothesized to be a deterrent for humans, as consuming or touching it may result in sickness or infection.[4] Human perception of the odor may be contrasted by a non-human animal's perception of it; for example, an animal who eats feces may be attracted to its odor.