Main chemical substances causing bad breath (volatile sulfur compounds):

 - Methylmercaptan (CH3SH)
 - Sulphydrate (SH2)
 - Dimethylsulphite (CH3)2S


Substances with a high potential of olfactory stimulation (usually produced during putrefaction):

 - Phenol
 - Indol
 - Skatole
 - Putrescine
 - Cadaverine
 - Hydrocarbons of the methane series

Substances produced by the putrefying effect of bacteria on protein compounds which are common in the human body:

PROTEOLITIC     +   SALIVA  +     PROTEIN    =       SULFUR
 BACTERIA                                   PEPTIDES         AMINO ACIDS

Systemically originated foul-producing substances, from blood circulation, as a result of changes in metabolism:

 - Ammonia;
 - Nitrogen compounds;
 - Ketoacids;
 - Fatty acids.