Is a bad smell, lots of molecules of bacteria going into our lungs and landing on the furniture? Should we worry about hygiene when there's a whiff in the air?
In order to smell something there must be molecules in the air that can get into our nasal passages (not the lungs). Bad smells are not usually harmful, for example, when you smell bad meat it is the breakdown products of the meat you are smelling not the bacteria. By the way, many harmful substances (cyanide for example) have very pleasant smells.