While halitosis isn't exactly visible, it has a few hallmarks that are. If one's tongue is coated with a white, yellow or brown substance, bad breath may be likely.
The tongue can turn white for a number of reasons. Most of them have either dehydration or bacteria in common, or in some cases both, according to the Mayo Clinic. A coating on the tongue is caused by inflammation of the taste buds. As they swell and redden, the buds will collect food debris, dead cells and bacteria, giving it a whitish color.
The health authority says that a white coating may indicate dehydration, fever, excess alcohol consumption or smoking, all of which can cause bad breath by drying up the mouth's saliva supply. Without saliva to cleanse the palate, microbes begin to multiply on the tongue, creating a foul smell.
Infections like thrush or syphilis may also give the tongue a white appearance.
What if the tongue is brown or even black? If halitosis occurs with a tongue that appears dark or furry, this may be a condition known as lingua villosa nigra, in which the buds of the tongue overproduce a substance called keratin, causing them to grow unusually long.
While it is not a disease and is relatively harmless, just like tongue coatings of any color lingua villosa nigra can result in pungent bad breath.
Cleansing the smell of halitosis from the tongue and the palate may be as simple as using a specialty breath freshener after brushing.