Are you one of those hosts who are immediately gripped by this conundrum as your guests step across the threshold into your home: Should you, or shouldn't you, ask them to remove their shoes?
身為主人的你，有沒有這種困擾：客人要進家門了，該不該請他脫鞋呢？
On the one hand, it makes you look like a fussy host. On the other, what about the legions of disease-causing bacteria that will gleefully leap off their shoes and inevitably infest your home?
請他脫鞋，顯得自己很麻煩；不說的話，致病「菌團」從鞋子上掉落，不可避免地把家裡弄髒怎麼辦？
Avoiding bacterial invasion at the risk of a little social awkwardness seems like a no-brainer. But are shoe bacteria something we should really be worried about in our homes? Here's what science tells us about how to navigate this conundrum.
以微小的社交尷尬來避免細菌侵襲，顯得簡單可行。可是，我們真的需要擔心室內從鞋底掉落的細菌嗎？就讓科學來告訴我們怎樣解決這個煩惱。
To start with, there's no point in sugarcoating the pill: the average shoe harbors "hundreds of thousands of bacteria per square inch", according to Jonathan Sexton, an environmental microbiologist and research specialist at the University of Arizona.
讓我們從亞利桑那大學環境微生物學家和研究專家喬納森·塞克斯頓開始。他說花言巧語毫無意義，因為普通鞋子的「每一平方英寸都有數十萬的細菌。」
The soles of our shoes are essentially a meet and greet for these microbes, and with each step we take, we pick up new attendants. "Pretty much wherever you go, you're going to be picking up stuff," Sexton told Live Science.
我們的鞋底基本上是微生物的聚集地。每走一步，都會吸納新成員。塞克頓斯告訴趣味科學：「不論你走到哪裡，鞋底都會沾到細菌。」
Beware, however: Some places like bathrooms do harbor more bacteria and a greater diversity, he said.
然而他還提醒，像浴室等地方聚集著更多更密的細菌。
But exactly what types of bacterial communities are hanging out on our shoes, and do they pose a legitimate health threat?
確切來說，我們鞋底的細菌群落是哪一種呢？它們真的威脅健康了嗎？
Well, previous studies have shown that (prepare yourself) almost all shoes in some research samples were coated with fecal bacteria, including one prominent bug called Escherichia coli (E.coli), which researchers discovered on 96 percent of shoe soles.
之前的研究表明，幾乎所有鞋子的研究樣本都帶有糞便細菌，其中包括家喻戶曉的大腸桿菌，發現於96%的鞋底下。
While many types of E.coli are harmless to humans, some strains can cause severe diarrhea, urinary tract infections and even meningitis. "Not necessarily on every shoe, but on a good majority, you can find some type of E.coli there," Sexton said.
雖然許多類別的大腸桿菌對人類是無害的，但也有一些菌株能引起嚴重腹瀉，尿路感染，甚至腦膜炎。塞克頓斯說：「不是每一雙鞋子都有大腸桿菌，但在大部分鞋上，你可以發現某一類。」
Apart from this ubiquitous germ, other studies have also found evidence of things like Staphylococcus aureus, which underlies a wide range of skin infections, and more worryingly, infections of the blood and the heart.
除了大腸桿菌外，另一些研究也發現了金黃色葡萄球菌。這一病原菌能引起大面積的皮膚感染，更令人擔憂的是，它能引發血液和心臟感染。
Another prominent study published in 2014 in the journal Anaerobe sampled 30 households in Houston, Texas, for the presence of Clostridium difficile (C. difficile), a bacterium with a long lifespan that commonly causes bowel problems like diarrhea.
另外一項重要研究發表於2014年的《厭氧菌》期刊上。該研究以休斯頓的30戶家庭為樣本採集艱難梭菌。這是長壽命的菌種，通常引起如腹瀉等腸道疾病。
Of all the household items they sampled, the researchers found that shoes harbored more C. difficile than even the surface of a toilet — underscoring the power that grubby shoes could have to spread germs through a home.
在所有的家居用品樣本中，研究者們發現，艱難梭菌在鞋底的含量比馬桶表面還要多，因此我們低估了骯髒的鞋底在家中傳播細菌的能力。
But despite the horrifying picture this paints of microbe-infested interiors, the research doesn't actually give us anything too serious to worry about.
不過除了令人驚悚的微生物滋生的室內圖片，研究並未告訴我們其它太嚴重需要擔心的事。
While many of us might want to launch into a house-cleaning frenzy at the thought of a wayward shoe, the reality is that the load of bacteria our shoes bring indoors isn't typically high enough to make the average healthy person very sick.
一想到「任性」的鞋子，我們可能就想要瘋狂的大掃除。但說句實話，鞋底帶進屋子裡的細菌還不足以讓一個健康的普通人生病。
"For a healthy individual, bacteria on shoes likely pose no or minimal risk," said Kevin Garey, the author on the 2014 C. difficile study and professor at the University of Houston College of Pharmacy.
2014年艱難梭菌研究作者、休斯頓大學醫藥學院教授凱文·加裡說：「對於一個健康的個體，鞋底的細菌通常不會有影響，就算有也微乎其微。」
Usually, a person would need to come into contact with thousands of microbes from one harmful bacterial strain to actually become infected with something, Sexton added.
塞克斯頓補充說，通常一個健康的人需要接觸一種有害菌種的數千種微生物後，才會真正感染某種疾病。
Another point is that most of us don't spend a lot of time on the ground, where shoe bacteria dwell. "The exposure makes the poison. So if you're not exposed to it, you're not going to get sick from it," Sexton said.
另一個方面，大多數人們不會長時間站在鞋底細菌居住的地面上。塞克斯頓說：「接觸細菌會產生毒素。因此，如果你沒有暴露在細菌環境中，就不會因此生病。」
In some cases, layers of bacteria coating the floor can become "re-aerosolized" and enter the air we breathe, lifted by the draft from a window, for instance, Sexton explained.
根據塞克斯頓的解釋，在某些情況下，細菌像外套一樣穿在地板上，一陣風從窗戶中吹來，使得細菌重新霧化，進入呼空氣中。
That might increase infection risk. But the greatest threat really lies on the ground. "I'd be more worried about a child crawling around on the floor. For a healthy adult, it's not too big of an issue," Sexton said.
這會增加感染的風險，但最大的風險依然在於地面。塞克斯頓說：「我更擔心的是在地上爬行的小孩。因為對健康成年人來說，這都不是大事兒。」
Another group of people who may need to take extra precautions are those who are immunocompromised, meaning their defences against infection are lower than usual. "In a person who is at risk for infections — usually someone recently hospitalized — attention to good household cleaning can be important," said Garey.
另一類需要預防的是免疫功能低下人群，他們對感染的抵抗力比普通人低。加裡說：「對於有感染風險的人群，特別是近期住過院的人，注重家庭衛生很重要。」
This is also why hospitals filled with vulnerable patients are much riskier environments to go venturing into with shoes, as there are more harmful germs there that can glob onto your soles.
這也是為何在充滿易受感染病人的醫院環境，穿著鞋子進去更加危險。因為更多有害細菌會粘在鞋底上。
In summary, if you're at risk of infection, or have a small child, "it would be a good idea to take your outdoor shoes off when you enter your home," Garey told Live Science.
加裡告訴趣味科學，總的來說，如果有感染風險或家裡有小孩，「進門脫鞋是很好的做法。」
"For most healthy persons, however, you can make the decision as much based on preference and habit, as potential health concern."
「對於大多數健康人來說，可以依據自己的偏好習慣，或對潛在健康問題的考慮基礎上做決定。」
For those whose health is at risk — or those simply too grossed out by the idea of uninvited bacteria in their homes — simply taking off your shoes, cleaning them once in a while and keeping houses clear of dust (a favorite food for bacteria) are good steps to take, Sexton said.
薩克斯頓說，對那些存在健康威脅，或十分厭惡家裡存在細菌的人，進門前脫鞋子，偶爾清洗鞋子，以及保持屋子纖塵不染（灰塵是細菌的摯愛）都是很好的辦法。
"It's always good to take precautions. But I don't recommend people go overboard with it."
「提前預防是很好的措施，但也不能過火。」
The consensus, then, is that for the average household, shoe bacteria don't pose an immediate risk.
有一個共識：鞋底的細菌並不會立刻影響一個普通家庭。
And it's worth remembering that bacteria exist elsewhere than on our shoes: They're in the air, on our skin, in our hair and inside our very guts.
有必要記住一點：細菌存在於任何地方，不僅是在鞋底，還在空氣，皮膚表面，頭髮以及我們的腸道中。
In fact, we live in a constantly swirling bacterial soup that would be impossible to completely disinfect. And would we want to, when we consider that thousands of these microbes are actually important for our well-being?
實際上，我們生活在不斷打旋的細菌濃湯中，因此想要完全不被感染是不可能的。但當我們想起上千種微生物對我們的健康十分重要時，我們還會這麼想嗎？
"Healthy bacteria in our gut, skin and elsewhere keep us healthy and protect us from other bacteria that can cause us illness," Garey said. "I don't think everyone appreciates that some bacteria are also good for us."
加裡說：「健康的菌種生活在我們的腸道、皮膚和其它身體部位，保衛我們的健康，保護我們遠離其它細菌引起的疾病。在我看來，並不是所有人都認同一些細菌對人體有益。」
Editor: Zhang Xi
Intern: Chen Xianglan
Click here for audio and translation of the story