O6 
The occurrence and cause of extra‐oral halitosis

Objective  Oral malodor is now generally accepted to be the main cause (about 90%) of bad breath. Bacterial formation of the volatile sulfur compounds hydrogen sulfide (H2S) and methylmercaptan (MM, CH3SH) within the oral cavity is the main cause of oral malodor. The objective was to study the occurrence and cause of the less well‐known extra‐oral halitosis.Methods  We investigated the mouth‐ and nose‐breath of 59 subjects complaining of bad breath and visiting our bad breath clinic. The methods used were gas chromatography and organoleptic scoring (OLS).Results  Six of 59 patients (10 %) were found to have extra‐oral halitosis. The concentrations of H2S and MM in mouth‐breath of patients with extra‐oral halitosis were very low and below critical odorous levels. H2S and MM were absent in nose‐breath of all patients. The concentration of dimethylsulfide (DMS, CH3SCH3) in mouth‐ and nose‐breath in the six patients with extra‐oral halitosis amounted to 1.57 ± 1.31 (s.d.) and 1.64 ± 1.29 nmol l−1 (range: 0.50–4.50), respectively, compared to 0.29 ± 0.19 and 0.21 ± 0.12 nmol l−1, respectively, in patients with oral malodor. The critical odorous concentration of DMS is about 0.5 nmol l−1. Simulated DMS gas‐mixtures had the same smell as observed in the extra‐oral halitosis patients. In these six patients good to perfect correlations were found between the OLS of mouth‐ and nose‐breath (simple correlation coefficient r = 0.840, P < 0.05), between mouth‐OLS and the concentration of DMS in mouth‐breath (r = 0.794, P < 0.05) and in nose‐breath (r = 0.824, P < 0.05) and between nose‐OLS and the concentration of DMS in mouth‐breath (r = 0.963, P < 0.001) and in nose‐breath (r = 0.955, P < 0.001). A perfect correlation was obtained between mouth‐ and nose‐DMS (r = 0.994, P < 0.001), indicating that DMS does not originate in the mouth . The origin of DMS must be found elsewhere, most probably in the blood.Conclusions  About 5–10% of patients with chronic halitosis has extra‐oral halitosis. In all patients with extra‐oral halitosis seen thus far, DMS was always the cause of bad breath. Other causes known, such as trimethylamine in the fish‐odor syndrome, are very rare.