Sulfur producing bacteria is the main cause for bad breath. Bad breath or halitosis usually develops slowly over time, and you may not even notice you have it.
Plaque and calculus
The plaque and calculus contain odor producing bacteria that causes the smell associated with bad breath.
The plaque forms around the teeth but can form on the tongue especially if there are grooves and fissures on the tongue surface.
Tonsils are another culprit for bad breath. Tonsils tend to have grooves and fissures where tonsil stones form from the minerals in the saliva and the bacteria in the mouth.
If you often get tonsillitis you need to visit your family physician to have an assessment.
Fungal and viral
Fungal and viral infection can form in the oral cavity, and this can relate to a certain smell. Denture wearers are more prone to fungal infection.
Food ingested will have a lingering odor, certain foods such as garlic, onions and fish have a dominant scent.
While certain habits such as smoking will also leave a residual odor. Acid reflux has a sour odor and putrid smell and is very noticeable.
Brushing is the best way to remove the plaque. Plaque can spread onto the tongue and gingiva and therefore gentle brushing and scraping is necessary.
A fungal or viral infection may require medication to clear.
Calculus is very tenacious and does not come off with regular brushing. A dental hygienist can remove it scalers.