Roaches cause sweet, musty, unpleasant odors. A full infestation in an area like a basement will produce a pungent sweet smell, but even a single German cockroach can cause this unpleasant smell. Roaches use chemicals, found on their legs and bodies, to communicate with other roaches about shelter, food, and mates. These chemicals release a musty scent which can linger in shed skins and feces. Dead roaches contribute to this odor as well—the oleic acid released during decomposition makes the sweet scent even stronger.