There is a curse that has plagued humanity since ancient times. The Greeks fought it by chewing aromatic resins, while the Chinese resorted to egg shells. In the ancient Jewish Talmud, it's even considered legal grounds for divorce. This horrible scourge is halitosis, otherwise known as bad breath. But what causes it, and why is it so universally terrifying? Well, think of some of the worst odors you can imagine, like garbage, feces or rotting meat. All of these smells come from the activity of microorganisms, particularly bacteria, and, as disgusting as it may sound, similar bacteria live in the moisture-rich environment of your mouth. Don't panic. The presence of bacteria in your body is not only normal, it's actually vital for all sorts of things, like digestion and disease prevention. But like all living things, bacteria need to eat. The bacteria in your mouth feed off of mucus, food remnants, and dead tissue cells. In order to absorb nutrients through their cell membranes, they must break down the organic matter into much smaller molecules. For example, they'll break proteins into their component amino acids and then break those down even further into various compounds. Some of the foul-smelling byproducts of these reactions, such as hydrogen sulfide and cadaverine, escape into the air and waft their way towards unsuspecting noses. Our sensitivity to these odors and interpretation of them as bad smells may be an evolutionary mechanism warning us of rotten food and the presence of disease. Smell is one of our most intimate and primal senses, playing a huge role in our attraction to potential mates. In one poll, 59% of men and 70% of women said they wouldn't go on a date with someone who has bad breath, which may be why Americans alone spend $1 billion a year on various breath products. Fortunately, most bad breath is easily treated. The worst smelling byproducts come from gram-negative bacteria that live in the spaces between gums and teeth and on the back of the tongue. By brushing and flossing our teeth, using antibacterial mouthwash at bedtime, gently cleaning the back of the tongue with a plastic scraper and even just eating a healthy breakfast, we can remove many of these bacteria and their food sources. 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. Behaviors like smoking and excessive alcohol consumption also have a very recognizable odor. Regardless of cause, the bad smell almost always originates in the mouth and not the stomach or elsewhere in the body. But one of the biggest challenges lies in actually determining how our breath smells in the first place, and it's unclear why. It may be that we're too acclimatized to the smell inside our own mouths to judge it. And methods like cupping your hands over your mouth, or licking and smelling your wrist don't work perfectly either. One study showed that even when people do this, they tend to rate the smell subjectively according to how bad they thought it was going to be. 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.
自古以来, 人类一直被一个诅咒缠绕。 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。 在古犹太教的《塔木德》文献, 它甚至是合法离婚的一个条件。 这个可怕的灾祸就是口臭。 但它是怎么样来的? 为什么它被所有人害怕着呢? 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。 所有的这些气味 来自微生物的活动, 特别是细菌, 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。 不要慌张。 你身体里有细菌 不但是再正常不过的事, 它们其实在很多方面上都必不可缺, 比如消化和预防疾病。 但跟其他生物一样, 细菌也需要食物。 在你口里的细菌以吃黏液、 食物残渣 和死的组织细胞生存。 为了从细胞膜吸收养分, 它们必须将有机物质 变成小一点的分子。 例如,它们会把蛋白质 打碎成它的要素胺基酸, 然后再把它们 变成更小的其他化合物。 有些从这个反应产生的臭的副产品, 像硫化氢和尸胺, 逃被释放到大气里 然后飘到 没有毫无防备预备的鼻子里。 我们对这些味道的敏感度和 辨别为臭味的举动 可能是一种进化的途径来 警告我们有腐烂的食物 和疾病。 气味是我们其中一个 最本质和原始的感官, 而它是未来伴侣的吸引中非常重要。 投票显示,59% 的男人和 70% 的女人 说他们不会跟一个有口臭的人约会, 那这就可以解释为什么美国人民 可以用上一亿美元来 买不同的口臭产品。 幸运的是,大部分的口臭 都能容易地解决。 最臭的副产品 来自格兰仕阴性的细菌, 它们住在牙床和牙齿之间的空隙 和舌头的底下。 刷牙和用牙线清洁牙齿、 睡觉前用抗菌的嗽口水、 用塑胶刮片轻轻地清洁舌头的底下 和甚至只吃一个健康的早餐, 我们可以除去很多这种细菌和 它们的食物来源 在某些情况,这些措施可能还不够 因为牙齿问题、鼻子的情况 或者旱见的病, 像肝病和没被控制的糖尿病。 生活习惯,例如吸烟和酗酒 都会有一股非常容易分辨的气味。 无论什么原因, 臭味差不多都是来自于口腔 而不是胃或身体的其他部分。 可是其中一个最大的挑战就在 实际决定我们的口气怎样变臭, 还有为什么。 可能我们对自己口里的气味太习惯了 所以才不能判断。 方法像把手盖在口上, 或者舔然后闻你的手腕 都不怎么有效。 研究显示即使人们这样做, 它们倾向于主观地 根据他们自己想像中气味 来评价那气味 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。