Halitosis: unpleasant breath. can be due to poor oral hygiene, local factors, or systemic involvement. Effects about 10-30% US population. Patients make an attempt to hide it with mints, chewing gum, compulsive brushing, and mouth rinses. Cause by retention of anaerobic gram-negative bacteria, hydrogen sulfide, methanethiol, diphenylamine, pyridine, and others.