Skip Navigation

How bad is your breath?

October 21, 2005 By Mark Peplow This article courtesy of Nature News.

A bioelectronic sensor can now tell you to three decimal places.

Hot date tonight... but how's your breath? To find out, you could soon be reaching for a trusty 'electronic nose' that can sniff out the smelliest chemical in your mouth.

"Humans are sensitive to halitosis in others but unable to assess the halitosis in their own breath," says Kohji Mitsubayashi, a bioengineer at Tokyo Medical and Dental University in Japan. It's a problem that is all too familiar to anyone who has ever exhaled into their cupped hands in a vain attempt to gauge their own oral hygiene.

But Mitsubayashi and his colleagues have now developed a sensor that can deliver precise readings of a sulphurous chemical called methyl mercaptan (CH3SH), a major cause of bad breath.

True halitosis is not simply a case of garlic breath or early morning dry-mouth. Methyl mercaptan is produced by bacteria, explains Jeffrey Coil, a halitosis expert from the University of British Columbia in Vancouver, Canada. The nasty niff is released as the microbes in your mouth munch proteins from food and your own dead cells.

Mitsubayashi's sensor relies on an enzyme called monoamine oxidase A, which digests methyl mercaptan in a chemical reaction that consumes oxygen. An oxygen-sensitive electrode monitors the reaction to reveal how much methyl mercaptan is in a patient's breath.

The sensor can detect concentrations of methyl mercaptan down to less than 1 part in ten million: that's more than twice as sensitive as the human nose. The team presents the device in the current issue of The Analyst1.

Sweet smell of success

The sensor will not only help would-be Romeos. The characteristic smell of methyl mercaptan can be a warning sign for gum disease, so dentists are keen to monitor halitosis in their patients. "But there are not many clinics in the world set up to measure these chemicals," says Coil.

Although halitosis can be reduced with a variety of antibacterial mouthwashes, Coil explains that the sensor would help to monitor the effectiveness of a particular treatment.

Some dentists already use machines that measure the concentration of all the sulphurous chemicals in your breath, but Coil points out that some patients may exhale high levels of less pungent sulphides, which can mask the true levels of methyl mercaptan itself.

Mitsubayashi adds that previous gas sensors have suffered from poor sensitivity, because of the moisture in a patient's breath. "Our biosniffers have good gas selectivity for medical and dental applications," he says. Their enzyme strongly prefers to feast on methyl mercaptan rather than other breath chemicals, and it is indifferent to exhaled water.

Coil agrees that Mitsubayashi's device could definitely be a boon. "Breath freshening is a billion-dollar industry," he says, "and any device that can differentiate this particular mercaptan would be beneficial."

Daily breath

It's all very well to know how bad your breath is, but how best to deal with it? "A lot of people think that brushing their teeth is important," says Coil. "But one of the most important places to clean is the back of the tongue," he advises, although he admits that many people find it difficult to overcome the gag reflex when brushing there.

Mitsubayashi thinks that the sensor will be used in dental hospitals at first, but in principle "the sniffer could be used for convenient halitosis assessment any time and anywhere in daily life".

The nose that knows could even become part of the relentless hybridization of the mobile telephone. "In the far future, the main system could be built into a cellphone, with a disposable sensitive tip supplied by the drugstore," Mitsubayashi suggests.


  1. Minamide T., et al. Analyst, 130. 1490 - 1495 (2005).


Need Assistance?

If you need help or have a question please use the links below to help resolve your problem.