There is a curse that has plagued humanity since ancient times.
自古以来，人类一直被一个诅咒缠绕。
The Greeks fought it by chewing aromatic resins, while the Chinese resorted to egg shells.
古希腊人以咀嚼有芳香的树脂对抗它，而中国人则依靠蛋壳。
In the ancient Jewish Talmud, it's even considered legal grounds for divorce.
在古犹太教的《塔木德》文献，它甚至是合法离婚的一个条件。
This horrible scourge is halitosis, otherwise known as bad breath.
这个可怕的灾祸就是口臭，也叫口腔异味。
But what causes it, and why is it so universally terrifying?
但它是怎么样来的？为什么它被所有人害怕着呢？
Well, think of some of the worst odors you can imagine, like garbage, feces or rotting meat.
那么想像一下世界上你觉得最臭的气味，例如垃圾、粪便或者腐烂的肉。
All of these smells come from the activity of microorganisms, particularly bacteria,
所有的这些气味来自微生物的活动，特别是细菌，
and, as disgusting as it may sound, similar bacteria live in the moisture-rich environment of your mouth.
虽然听起来不能再恶心，跟那些相似的细菌正住在你湿润的口腔里。
Don't panic. The presence of bacteria in your body is not only normal,
不要慌张。你身体里有细菌不但是再正常不过的事，
it's actually vital for all sorts of things, like digestion and disease prevention.
而且它们其实在很多方面上都必不可缺，比如消化和预防疾病。
But like all living things, bacteria need to eat.
但跟其他生物一样，细菌也需要食物。
The bacteria in your mouth feed off of mucus, food remnants, and dead tissue cells.
在你口里的细菌以吃黏液、食物残渣和死的组织细胞生存。
In order to absorb nutrients through their cell membranes,
为了从细胞膜吸收养分，
they must break down the organic matter into much smaller molecules.
它们必须将有机物质变成小一点的分子。
For example, they'll break proteins into their component amino acids
例如，它们会把蛋白质打碎成它的要素胺基酸，
and then break those down even further into various compounds.
然后再把它们变成更小的其他化合物。
Some of the foul-smelling byproducts of these reactions,
有些从这个反应产生的臭的副产品，
such as hydrogen sulfide and cadaverine, escape into the air and waft their way towards unsuspecting noses.
像硫化氢和尸胺，逃放到大气里，然后飘到没有毫无防备的鼻子里。

Our sensitivity to these odors and interpretation of them as bad smells
我们对于这些味道的敏感度和恶臭气味的解读，
may be an evolutionary mechanism warning us of rotten food and the presence of disease.
可能是一种进化机制，警告我们腐烂食物与疾病的存在。
Smell is one of our most intimate and primal senses, playing a huge role in our attraction to potential mates.
嗅觉是我们最亲密的主要感觉之一，它扮演着吸引潜在伴侣的重要角色。
In one poll, 59% of men and 70% of women said they wouldn't go on a date with someone who has bad breath,
一个调查显示，有59%的男性和70%的女性不愿与有口臭的人约会，
which may be why Americans alone spend $1 billion a year on various breath products.
这可能是为什么仅仅美国人每年就花费十亿美元在各式改良口腔气息的产品上。
Fortunately, most bad breath is easily treated.
还好，大多数口臭很容易处理。
The worst smelling byproducts come from gram-negative bacteria
最糟糕的副产品气味来自革兰氏阴性菌，
that live in the spaces between gums and teeth and on the back of the tongue.
它存在于牙龈和牙齿的间隙以及舌头的后面。
By brushing and flossing our teeth, using antibacterial mouthwash at bedtime,
刷牙，用牙线清洁牙齿，睡前使用抗菌漱口水，
gently cleaning the back of the tongue with a plastic scraper and even just eating a healthy breakfast,
用塑料刮板轻轻清洁舌头的后部以及吃健康的早餐，
we can remove many of these bacteria and their food sources.
我们就可以去除许多细菌和它们的食物来源。
In some cases, these measures may not be enough
在某些情况下，这些做法还不够，
due to dental problems, nasal conditions, or rarer ailments, such as liver disease and uncontrolled diabetes.
由于牙齿的问题、鼻腔的状况或是罕见疾病，例如肝病和失控的糖尿病。
Behaviors like smoking and excessive alcohol consumption also have a very recognizable odor.
抽烟或过量饮酒也会产生可明显的气味。
Regardless of cause, the bad smell almost always originates in the mouth and not the stomach or elsewhere in the body.
无论什么原因，臭味几乎都来自嘴巴，而不是胃或身体其他部位。
But one of the biggest challenges lies in actually determining how our breath smells in the first place, and it's unclear why.
但最大的挑战之一在于确任我们的口腔气息如何及其原因。
It may be that we're too acclimatized to the smell inside our own mouths to judge it.
或许我们太习惯自己口腔的气味，以致无法判断。
And methods like cupping your hands over your mouth, or licking and smelling your wrist don't work perfectly either.
而像是用手掩盖嘴巴自闻或是舔闻手腕，这些方法都不准确。
One study showed that even when people do this,
一项研究显示，当人们如此做时，
they tend to rate the smell subjectively according to how bad they thought it was going to be.
他们倾向于主观地根据他们自己想像中气味来评价那气味。
But there's one simple, if socially difficult, way of finding out how your breath smells: just take a deep breath and ask a friend.
但是有一种简单的，但是在社交场合中很困难的方法来知道你的口气闻起来怎样：只要深呼吸然后问你的朋友。