One of the prime indicators of a tonsil stone is exceedingly bad breath, or halitosis, that accompanies a tonsil infection. One study of patients with a form of chronic tonsillitis used a special test to see if volatile sulfur compounds were contained in the subjects' breath. The presence of these foul-smelling compounds provides evidence of bad breath. The researchers found that 75% of the people who had abnormally high concentrations of these compounds also had tonsil stones. Other researchers have suggested that tonsil stones be considered in situations when the cause of bad breath is in question.