Halitosis isn't an odor in the usual sense — it's a measurable group of gases. The three primary culprits are volatile sulfur compounds (VSCs): hydrogen sulfide (H₂S), methyl mercaptan (CH₃SH), and dimethyl sulfide ((CH₃)₂S). Each is produced by anaerobic bacteria breaking down sulfur-containing amino acids in the mouth, and each tells us something different about where the breath odor is actually coming from.
The three VSCs and what they signal
- Hydrogen sulfide (H₂S) — rotten-egg smell. Most commonly produced by tongue-coating bacteria on the dorsum of the tongue. Often the first VSC to drop with effective tongue scraping.
- Methyl mercaptan (CH₃SH) — sulfurous, cabbage-like smell. Strongly associated with periodontal disease and subgingival bacterial activity. Elevated methyl mercaptan in the absence of obvious tongue coating points to gum disease as the dominant source.
- Dimethyl sulfide ((CH₃)₂S) — sweet or onion-like smell. Often associated with sinus or systemic sources, including liver dysfunction. Elevated dimethyl sulfide warrants a sinus or medical workup beyond the dental exam.
How we measure them
A halimeter is a portable sulfide monitor that measures VSCs in parts per billion. The patient breathes through a disposable straw into a sensor; the device reads in real time. We take baseline readings at the diagnostic visit and re-test at 6 weeks to confirm the treatment protocol is working — objective progress, not patient self-report.
What the numbers mean
- Below 75 ppb — normal range. Halimeter readings at this level indicate breath that is unlikely to be detectable by others.
- 75 – 150 ppb — mild halitosis. Often responds well to home-care reform alone.
- 150 – 300 ppb — moderate halitosis. Almost always requires clinical treatment alongside home care.
- Above 300 ppb — severe halitosis. Periodontal, sinus, or systemic source is highly likely.
Why this matters for treatment
Halitosis treatment without measurement is guesswork. Two patients with the same subjective complaint can have different dominant VSCs and need different protocols — one targeting tongue bacteria, one targeting periodontal pockets, one referred to ENT or a physician. The halimeter is what makes that distinction visible.
Read more about our halitosis treatment programs or schedule a diagnostic exam to get your baseline reading.
Last reviewed by Dr. Teah Nguyen, DDS — May 2026.