Our body’s ability to sense chemicals is another chemosensory mechanism that contributes to our senses of smell and taste. In this system, thousands of free nerve endings especially on the moist surfaces of the eyes, nose, mouth, and throat identify sensations like the sting of ammonia, the coolness of menthol, and the heat of chili peppers.
The medical condition dry mouth (also called xerostomia) also can cause bad breath. Saliva is necessary to moisten the mouth, neutralize acids produced by plaque, and wash away dead cells that build up on the tongue, gums, and cheeks. If not removed, these cells decompose and can cause bad breath. Dry mouth may be a side effect of various medications, salivary gland problems, or continuous breathing through the mouth. In fact, morning breath is worse for people who sleep with their mouths open.

Bad breath is often evaluated by a dentist. In addition to patient history and physical examination of the mouth, tests may be needed to diagnose the cause of bad breath, such as: Organoleptic testing: assesses the strength of bad breath Sulfide monitors to measure mouth-air volatile sulfur compound (VSC) content, which are produced by anaerobic bacteria from food debris in the mouth that cause bad breath Gas chromatography to measure VSCs X-rays of the mouth Periodontal charting if gum disease is suspected Brush and floss twice daily Mouthwash Can help kill bacteria or neutralize and mask bad breath Mouthwash is only a temporary solution Clean dentures regularly and thoroughly Keep saliva flowing Chew sugar-free gum or suck on sugar-free hard candy Eat healthy foods that require a lot of chewing, such as carrots or apples Use artificial saliva if your dentist recommends it Don’t smoke See your dentist regularly https://www.mouthhealthy.org/en/az-topics/b/bad-breath https://www.uptodate.com/contents/bad-breath?search=bad%20breath&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H2120250223 https://www.healthgrades.com/right-care/oral-health/6-surprising-causes-of-bad-breath#:~:text=A%20diet%20very%20high%20in,unpleasant%20odor%20from%20your%20mouth.&text=There%20are%20many%20types%20of,turn%20leads%20to%20bad%20breath
Gum disease, also known as periodontal disease, is another common cause of halitosis. When plaque builds up on the teeth and gums, it can lead to inflammation and infection. This can result in an unpleasant odor coming from the mouth. Certain medical conditions such as dry mouth, sinus infections, and respiratory tract infections can also contribute to bad breath.