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.
人類自古以來即苦於此詛咒 希臘人咀嚼芳香樹脂來對付它 中國人則是用蛋殼 依據古猶太法典 這可以是離婚的合法理由 這可怕的禍害是口臭 也就是口氣難聞 造成原因是什麼? 為何口臭普遍被認為可怕呢? 想像一些最難聞的氣味 如垃圾、糞、腐肉 這些氣味都來自微生物的活動 尤其細菌的活動 儘管聽起來噁心 類似的細菌就住在口腔 這類潮濕的環境裡 不要驚慌 身體裡有細菌存在,不僅正常 而且事實上對於生命諸事 例如消化、預防疾病等等 都非常地重要 如同所有的生物 細菌需要吃東西 口中的細菌進食黏液 食物殘渣 和死掉的細胞組織 為了透過細胞膜吸收養分 細菌必須把有機物 分解為更小的分子 例如把蛋白質分解成氨基酸 然後更進一步 分解成各種化合物 這些反應產生一些 帶著惡臭的副產物 例如硫化氫和屍胺 逸到空氣中 飄向毫無防備的鼻子 我們對於這些味道的敏感度 和惡臭氣味的解讀 可能是一種進化機制 警告我們腐爛食物 與疾病的存在 嗅覺是我們最親密的主要感覺之一 它扮演著吸引 潛在伴侶的重要角色 一個調查顯示 有59%的男人和70%的女人 不願與有口臭的人約會 這可能是為什麼僅僅美國人 每年就花費十億美元 在各式改良口腔氣息的產品上 還好,大多數口臭很容易處理 最糟糕的副產品氣味 來自革蘭氏陰性菌 存在於牙齦和牙齒的間隙 以及舌頭的後面 刷牙、用牙線清潔牙齒 睡前使用抗菌漱口水 用塑料刮板輕輕清潔 舌頭的後部 以及吃健康的早餐 我們就可以去除許多細菌 和它們的食物來源 在某些情況下,這些做法還不夠 由於牙齒的問題、鼻腔的狀況 或是罕見疾病 例如肝病和失控的糖尿病 抽煙或過量飲酒 也會產生可明顯的氣味 無論什麼原因 臭味幾乎都來自嘴巴 而不是胃或身體其他部位 但最大的挑戰之一在於 確任我們的口腔氣息如何 及其原因 或許我們太習慣 自己口腔的氣味 以致無法判斷 而像是用手掩蓋嘴巴自聞 或是舔聞手腕 這些方法都不準確 一項研究顯示 當人們如此做時 他們傾向於以 自認為會有多糟 主觀地判斷氣味程度 有一個做起來容易 但社交上卻不適切 能夠確知你的口氣聞起來如何 大大的呼出一口氣 然後詢問朋友