Most bad breath is caused by an overgrowth of anaerobic bacteria (strains that don't need oxygen to survive) in saliva that produce foul-smelling, sulfurous compounds. The bacteria - which coat the mouth, teeth, and tongue - release the compounds as they feed on food residue. Postnasal drip or infections such as sinusitis can also make your breath reek from bacteria, as can dry mouth, which leaves less saliva to wash away the food particles bacteria feed on and less moisture to mask odour. If you suspect your breath is a little less than fresh, lick the back of your hand, then smell it: If it has an odour, you know your breath does, too. The following steps can help.