Does Your Breath Smell? It May Be Genetic

A stack of black garlic in France THIERRY ZOCCOLAN/AFP/Getty Images

Most people would tell you that bad breath is brought on by a combination of bad luck and garlic. According to a new study in Nature Genetics, genes may play a direct role as well. Researchers at U.C. Davis have found that a the gene for a protein known as a SELENBP1 may be implicated in bad (specifically cabbage-scented) breath, Gizmodo reports. The protein may also play a rule in a few kinds of cancers, so the stakes may be a little higher down the line.

The researchers looked at five human patients from three different families who had "cabbage-like breath odor." Turns out, they all had mutations in the gene that codes for SELENBP1.

After eliminating other possible causes of bad breath, the researchers had each participant breathe through a machine that was able to separate out the source of the smell: the culprits were methanethiol and dimethylsulfide, two compounds that contain sulfur.

The kinds of sulfur compounds found in organic matter can smell pretty bad, as anyone who's ever sniffed a rotten egg can attest to. (The Minnesota Department of Health warns that the smell of rotten eggs coming from a faucet can be a tipoff to the presence of hydrogen sulfide gas in a person's water supply).

Once the scientists figured out that the five stink-breathed humans had this trait in common, they wanted to get a better sense of what SELENBP1 did. So, they bred some mice who didn't have the gene. And, lo and behold, the mice had higher levels of sulfur compounds in their blood (the researchers, as far as Newsweek can tell, did not smell the breath of each mouse).

With that evidence, the researchers make the case that lack of SELENBP1 can cause bad breath. But other than providing fodder for a fun science experiment, why would the human body have a gene whose absence makes people's breath smell?

"The function of SELENBP1 might possibly be keeping the breath methanethiol concentration low, thus enabling the human nose to detect foul smells from environmental volatile sulfur compounds," the researchers write.

As Gizmodo points out, this is a single research study, and the gene-knockout piece was carried out in mice, not human beings. So, handle with caution. All the same, according to a study from the BMJ published in 2006, 8 to 50 percent of people in the "developed world...perceive that they have persistent recurrent episodes of oral malodor." Now, there's a chance at least some of them may one day know why.