Cysteine challenge test as a novel diagnostic tool to distinguish oral halitosis

Aust Dent J. 2022 Mar;67(1):69-75. doi: 10.1111/adj.12884. Epub 2021 Nov 17.


Background: The cysteine challenge test is often used to check the H2 S production capacity of the mouth. Patients with oral halitosis group (n = 305) or non-oral halitosis group (n = 191) and healthy individuals (control group, n = 102) were compared with each other to identify any possible relationship between initial and cysteine-induced oral H2 S concentrations.

Subjects and method: The medical records of 598 participants were reviewed retrospectively. Oral H2 S concentrations before (pre-CR) and after cysteine rinse (post-CR) with 5 mL of 20 mmol L-cysteine solution for 30 s were compared.

Results: Pre-CR H2 S concentrations were >0.8 ppm in 75.1% of oral group patients but less than <0.8 ppm in 87.3% of the non-oral group and 86.9% of controls. After cysteine rinse, oral H2 S concentrations exceeded 12 ppm in 72% of the oral halitosis patients but were lower in 88% of non-oral group and 99% of controls. Whilst post-CR/pre-CR ratio was >12 in 74.5% of the oral group, it was <12 in 81.7% of the non-oral group and 83.4% of controls.

Conclusion: Cysteine challenge test can be used as a diagnostic tool to identify an individual's tendency to produce oral malodor, not only to quantify momentary halitosis level.

Keywords: Bad breath; differential diagnosis; halitosis; hydrogen sulphide; oral malodor.

MeSH terms

  • Cysteine*
  • Halitosis* / diagnosis
  • Humans
  • Mouth
  • Retrospective Studies


  • Cysteine