It might not be the garlic or onions, coffee or alcohol. Rather, a new study links it to the types of bacteria that dominate the back portion of the top of your tongue.

Some bacteria protect against halitosis, the formal name for really bad breath, while others cause the pungent odor, says a team of researchers from The Forsyth Institute in Boston.

"I think there's a definite smoking gun here -- that it's a strong association," says lead researcher Bruce Paster. "There are the good bacteria and the bad ones."

The study, reported in the February issue of the Journal of Clinical Microbiology, relied on gene sequencing to compare bacteria found on the tongues of those with halitosis and those with fresh breath.

Researchers reported species of the same three bacteria were prevalent among five people with fresh breath. The most common of these germs found on these subjects' tongues, Streptococcus salivarius, appeared in only one of six people with halitosis -- and at extremely low levels.

Six species of bacteria were linked to halitosis, and several of those germs were not found in those with fresh breath.

About 65 million Americans suffer from halitosis at some point in their lives, the National Institute of Dental Research has estimated.

研究发现，口腔异味并不一定是因为大蒜、洋葱、咖啡或酒精引起的，罪魁祸首有可能是位于舌尖背部的几种特殊类型的细菌。

来自波士顿福塞斯研究所的一个研究小组发现，口腔内有一些细菌可以防止口臭，也就是口腔异味的产生，而另一些的作用则刚好相反。

研究小组的领导者布鲁斯·帕斯特说："我们有确凿的证据表明--口气和这些细菌之间是有联系的。有的细菌能令口气清新，同时也有能引起口臭的细菌。"

这一研究结果发表在二月的《临床微生物学》杂志上。文中，研究人员是通过基因序列比较口气有异味和无异味人群口腔内的细菌种类来论证这一结论的。

研究人员发现，在五名没有口臭的试验对象口腔中，都有同样的三种细菌，其中含量最高的是唾液链球菌。而在六名有口臭的人士中，只有一个人的口腔中有这种细菌，而且含量很低。

研究人员共发现了六种能引起口臭的细菌，其中几种是口气清新的人口中所没有的。

据美国国家牙科研究所估算，约6千5百万美国人有不同程度的口臭。