Which gases make bad breath bad?

When you smell someone's bad breath, your nose detects and your brain takes note of thousands of different compounds, most of which have little or no odor. However, it only takes a few notorious gases - or even just one, really - to give a person some seriously repulsive halitosis.

Below are the gases that make your bad breath a pungent reality. Not to worry: you can always use alcohol-free specialty breath freshening products to neutralize these smelly compounds, as well as oral care probiotics to prevent bacteria from cranking them out in the first place.

Here are the usual suspects:

Hydrogen sulfide - As far as bad breath goes, this molecule might as well be considered Public Enemy Number One. When the microbes in your mouth multiply, they emit many volatile sulfur compounds (VSCs), and hydrogen sulfide is possibly the most plentiful. The name may not ring any bells, but get one whiff of the stuff, and your nose will remind you that, yes, you you're quite familiar with the gas.

You see, hydrogen sulfide is responsible for the scent of rotten eggs, according to the Occupational Safety and Health Administration. The agency states that other names for this gas include "swamp gas" and "sewer gas." The latter being fairly apropos, since that is essentially what microorganisms are using your mouth as - namely, a sewer. What they deposit are VSCs.

Dimethyl sulfide - This is another common VSC in bad breath, one that specialty breath fresheners can eliminate by neutralizing it on contact. Dimethyl sulfide has a distinct odor of its own. According to the Good Scent Company (GSC), this aromatic compound gives cabbage and seafood its distinct smell.

Methyl mercaptan - This molecule creates quite a stink, whether it's in garlic, seafood or cabbage (all common source of the compound). The GSC laconically describes its smell as "stench."

The organization also characterizes it as "slightly skunk-like" or smelling like asparagus. In fact, methyl mercaptan gives your body's effluvia the unmistakable smell of asparagus, perhaps the gas's most potent source. How do we know this? In the 1980s, a team of researchers asked 100 French men and women to eat asparagus. The ultimate result, as described in the British Journal of Clinical Pharmacology, was lots of methyl mercaptan.

This gas packs quite a wallop. Methyl mercaptan is possibly the most pungent, if not the most common, of all the gases in bad breath, according to a study published in the Kathmandu University Medical Journal.