There is a curse that has plagued humanity since ancient times.
从古代起就有一种“诅咒”一直让人类饱受折磨。
The Greeks fought it by chewing aromatic resins, while the Chinese resorted to egg shells.
古希腊人通过咀嚼芳香树脂来对抗它，而古代的中国人使用的则是鸡蛋壳。
In the ancient Jewish Talmud, it's even considered legal grounds for divorce.
在古犹太法典中，它甚至成为了合法的离婚理由。
This horrible scourge is halitosis, otherwise known as bad breath.
这种可怕的折磨就是口气异常，也被称为口臭。
But what causes it, and why is it so universally terrifying?
但是它是如何产生的呢？为什么它如此普遍地令人生畏？
Well, think of some of the worst odors you can imagine, like garbage, feces or rotting meat.
想一想你能想象到的一些最难闻的气味，比如垃圾、排泄物或者腐坏的肉。
All of these smells come from the activity of microorganisms, particularly bacteria, and,
所有这些味道都来自微生物，特别是细菌的活动，
as disgusting as it may sound, similar bacteria live in the moisture-rich environment of your mouth.
尽管听起来很恶心，但是相似的细菌就生活在你的嘴里这个湿润的环境中。
Don't panic. The presence of bacteria in your body is not only normal,
别慌。细菌存在于你的身体中不仅再正常不过了，
it's actually vital for all sorts of things, like digestion and disease prevention.
而且事实上，它对很多事情都是至关重要的，比如消化和疾病预防。
But like all living things, bacteria need to eat.
但是和所有活着的事物一样，细菌需要进食。
The bacteria in your mouth feed off of mucus, food remnants, and dead tissue cells.
你嘴里的细菌以粘液、食物残渣和死亡的组织细胞为食。
In order to absorb nutrients through their cell membranes,
为了通过它们的细胞膜吸收养分，
they must break down the organic matter into much smaller molecules.
这些细菌必须把有机质分解成更小的分子。
For example, they'll break proteins into their component amino acids
比如，它们会把蛋白质分解成氨基酸成分，
and then break those down even further into various compounds.
然后再把这些更进一步分解成各种化合物。
Some of the foul-smelling byproducts of these reactions,
这些反应中产生的一些难闻的副产品，
such as hydrogen sulfide and cadaverine, escape into the air and waft their way towards unsuspecting noses.
比如硫化氢和尸胺，会逃进空气中并一路飘到毫无戒备的鼻子里。
Our sensitivity to these odors and interpretation of them as bad smells may be an evolutionary mechanism
我们对这些气味的敏感度以及将它们认知为难闻气味的行为也许是一种进化机制，
warning us of rotten food and the presence of disease.
提醒我们注意腐坏的食物和疾病的存在。
Smell is one of our most intimate and primal senses, playing a huge role in our attraction to potential mates.
嗅觉是我们最私人和原始的感官之一，它在我们吸引潜在配偶时发挥着巨大的作用。
In one poll, 59% of men and 70% of women said they wouldn't go on a date with someone who has bad breath,
在一项民意测验中，59%的男性和70%的女性表示他们不会和有口臭的人约会，
which may be why Americans alone spend $1 billion a year on various breath products.
而这也许就是美国人一年在各种除口臭产品上的花费达十亿美元的原因。
Fortunately, most bad breath is easily treated.
好在大部分口臭问题都很容易对付。
The worst smelling byproducts come from gram-negative bacteria
最难闻的副产品是由革兰氏阴性菌产生的，
that live in the spaces between gums and teeth and on the back of the tongue.
它们生活在牙床和牙齿之间，以及舌头背面的位置。
By brushing and flossing our teeth, using antibacterial mouthwash at bedtime,
只要刷牙和用牙线洁牙，上床睡觉前使用杀菌漱口水，
gently cleaning the back of the tongue with a plastic scraper and even just eating a healthy breakfast,
用塑料刮板轻轻地清洁舌背，甚至只是吃一顿健康的早餐，
we can remove many of these bacteria and their food sources.
我们都能清除很多细菌及它们的食物来源。
In some cases, these measures may not be enough due to dental problems, nasal conditions, or rarer ailments, such as liver disease and uncontrolled diabetes.
在某些情况下，由于牙齿问题、鼻腔情况或像肝病和糖尿病这样的较罕见疾病，这些措施也许远远不够。
Behaviors like smoking and excessive alcohol consumption also have a very recognizable odor.
像抽烟和过度饮酒这样的行为也会产生一种非常明显的气味。
Regardless of cause, the bad smell almost always originates in the mouth
抛开原因不看，难闻的气味几乎总是在嘴巴里产生的，
and not the stomach or elsewhere in the body.
而不是胃或身体的其他部位。
But one of the biggest challenges lies in actually determining how our breath smells in the first place, and it's unclear why.
但是最大的挑战之一在于，真正决定我们口气是什么样的，其原因至今不明。
It may be that we're too acclimatized to the smell inside our own mouths to judge it.
也许是因为我们对自己嘴巴里的味道太过熟悉，以至于无法判断。
And methods like cupping your hands over your mouth,
像把双手合拢放在嘴前对着哈气，
or licking and smelling your wrist don't work perfectly either.
或者舔一下手腕然后闻一下味道这样的方法也不是很有效。
One study showed that even when people do this,
一项研究显示，即使在人们这么做的时候，
they tend to rate the smell subjectively according to how bad they thought it was going to be.
他们往往会根据自己觉得味道会怎么样来主观地判定口气的难闻程度。
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.
但是有一种方法能弄明白你有没有口臭，虽然这种方法在社交上有些困难，但非常简单，那就是：深呼吸然后问问你的朋友。