Most scientists think that tonsils are responsible for bad breath in about 3-6% of cases.

Although tonsils sometimes have foul odor (for example when pressed), it is not clear to what extent this causes bad breath.

In some individuals, small deposits of calcified material (bacteria and their debris, in particular) accumulate in small cavities (crypts) on the surface of the tonsils. These deposits break away from the tonsils, and are coughed up as little stones. The medical term for these stones is "tonsillolith". These stones smell like hell (in fact their odor is similar to that coming from deep periodontal pockets). People who cough up these stones and then smell them are sure that their breath smells as bad as these stones. According to my experience, this is not the case. Rather, having smelly tonsilloliths often causes people to spend years, wrongly assuming that they must have bad breath. In any case, tonsilloliths can be alleviated by a medical treatment known as laser cryptolysis, in which the crypts are lased. However, since in almost all cases the tonsilloliths themselves do not necessarily constitute a medical problem, I am not convinced that everyone with tonsilloliths needs to undergo this procedure. Please keep in mind that I am not a medical doctor, and that if you are concerned about this problem, you should speak to a qualified physician.