你的床单多长时间洗一次呢？两星期？一个月？还是半年？
科学家给出了答案：一星期。
你的肉眼看不见，不代表你的床单不脏。如果床单超过一星期不洗，落在上面的各种细菌和真菌就会让你过敏甚至生病。
We spend more than a third of our lives in bed - but that place can quickly blossom into a "botanical park" of bacteria and fungus, according to New York University microbiologist Philip Tierno.
纽约大学的微生物学家菲利普·缇艾诺指出，我们有超过三分之一的人生都是在床上度过的，而我们的床可以迅速发展成细菌和真菌的“植物园”。
If left for too long, the microscopic life within the wrinkles and folds of our bed sheets can even make us sick, Tierno told Business Insider.
缇艾诺告诉商业内幕网说，如果床单太久不洗，床单皱褶里的微生物就会让我们生病。
To stem the invisible tide, he said sheets should be washed once a week.
为了防范于未然，他表示床单应该每周洗一次。
Humans naturally produce roughly 26 gallons of sweat in bed every year. When it's hot and humid outside, this moisture becomes what scientists call an "ideal fungal culture medium."
人类每年在床上自然分泌的汗液达26加仑。如果外面炎热潮湿，床上的湿度就会变成科学家所说的“理想的真菌培养基”。
In a recent study that assessed the level of fungal contamination in bedding, researchers found that feather and synthetic pillows between 1.5 and 20 years old can contain between four and 17 different species of fungus.
最近的一项研究评估了床上用品的真菌污染水平，研究人员发现，使用年限在1.5年和20年之间的羽绒和化纤枕头含有4到17种不同的真菌。
And it's not just your own microbial life you're sleeping with. In addition to the fungi and bacteria that come from your sweat, sputum, skin cells, and vaginal and anal excretions, you also share your bed with foreign microbes.
和你一起睡觉的不光是你身上的微生物。除了你的汗液、唾液、皮肤细胞、私处和肛门分泌物中的真菌和细菌，你还和外来微生物共享你的床。
These include animal dander, pollen, soil, lint, dust mite debris and faeces, and finishing agents from whatever your sheets are made from, to name a few.
这些外来微生物包括动物毛屑、花粉、泥土、线头、螨虫尸体和粪便，以及生产你的床单所用的整理剂，这些还只是其中一部分而已。
Tierno says all that gunk becomes "significant" in as little as a week. And unclean bedding still exposes you to materials that can trigger the sniffing and sneezing, since the microbes are so close to your mouth and nose that you're almost forced to breathe them in.
缇艾诺说，在短短一周的时间里，这些污物就会变得“严重”起来。不清洁的床单被罩会让你暴露在这些物质中，从而引发鼻炎和喷嚏，因为微生物离你的嘴和鼻子太近了，你几乎是被迫将它们吸进去。
"Even if you don't have allergies per se, you can have an allergic response," Tierno said.
缇艾诺说：“即使你本人不是过敏体质，你也可能产生过敏反应。”
Another reason your sheets get dirty quickly has little to do with your behaviour or sweat patterns - the issue is simply gravity.
你的床单迅速变脏的另一个原因和你的行为或流汗模式没有太大关系，问题主要在于重力。
"Just like Rome overtime was buried with the debris that falls from gravity, gravity is what brings all that material into your mattress," Tierno said.
缇艾诺说：“就像罗马随着时间的流逝最终会被重力拉垮，被碎片掩埋，重力也将所有这些物质带到了你的床上。”
One to two weeks of this build-up is enough to leave anyone with a scratchy throat - especially those with significant allergies or asthma.
这些物质在床上累积一到两周就足以让任何人喉咙发痒，尤其是那些有严重过敏或哮喘病史的人。
"If you touched dog poo in the street, you'd want to wash your hands," said Tierno. "Consider that analogous to your bedding. If you saw what was there - but of course you don't see it - after a while you have to say to yourself, 'Do I want to sleep in that?'"
缇艾诺说：“如果你在街上碰了狗屎，你会想洗手。如果你的床单上粘上了不干净的东西呢？如果你看到了床单上的那些物质——当然你看不到——你得问问自己：‘我想睡在那张床上吗？’”