Microbiology and chemistry of oral halitosis

  • This is followed by further cleavage of certain amino acids to bad-smelling by-products of bacterial metabolism, predominantly volatile sulphur compounds (VSC) (hydrogen sulphide, methyl mercaptan and dimethyl sulphide), organic acids (butyric acid), aromatic compounds (indole, skatole) and amines (putrescine, cadaverine).

Formation of malodour products by oral anaerobic bacteria

  • The breakdown of the sulphur-containing amino acids cysteine and methionine produces the VSC hydrogen sulphide and methyl mercaptan, respectively.
  • VSC are significantly associated with oral malodour and usually decrease following successful treatment (Rosenberg 1996).
  • Amines are not considered to play an essential part in malodour formation because of their low volatility. Due to their basic pK level the amine groups of these compounds are present almost exclusively in protonated ionic form at the usually neutral pH in the oral cavity and thus kept in solution.