Dental and gum problems — such as decayed teeth, tartar buildup, bleeding gums, and poor oral hygiene — are common causes of bad breath.
Another potential cause is esophageal diverticula. These are pouch-like structures that sometimes form on the walls of the esophagus. Food particles can become trapped in these "pockets," where they decompose and produce a foul odor.
ENT (Ear, Nose, and Throat) conditions like chronic sinusitis, tonsillitis, and adenoiditis are also known to cause persistent bad breath.