解密：手指被纸划伤为什么那么疼？Why paper cuts hurt so much?

We're reading a book or opening an envelope when, all of a sudden, there's a sharp pain on our finger.

我们正在读书或拆分信封，突然，指尖传来一阵刺痛。

You see a little bit of blood and realize you've just gotten a paper cut.

看见溢出的血丝，才意识到刚刚纸片割伤了手指。

Dr Hayley Goldbach, a resident dermatologist at UCLA Health, spoke about why paper cuts are so jagged, how the element of surprise leaves us in more pain and how to make sure they heal quickly.

美国加州大学洛杉矶分校的皮肤科住院医师海莉·哥德巴赫谈论了：为何纸张割破的伤口呈锯齿状；出乎意料的心理因素怎样加剧疼痛；伤口怎样才能快速愈合。

Dr Goldbach explained that one reason paper cuts hurt so much is where they occur: primarily on the finger.

海莉医生解释，纸张割伤会如此疼痛的一个主要原因是伤口在指尖上。

"We have nerve endings all over the body," she said. "In places where there is refined movement and sensation — like the lips or tips of the fingers — they have a high density of nerve endings."

她说：“我们全身都有神经末梢。而在功能复杂精细的运动和感觉部位里，比如嘴唇和指尖，神经末梢的密度更大。”

These nerve endings are known as nociceptors and they send signals to the brain about things that could cause a break in the skin, such as extreme hot or cold temperatures and chemicals. 

这些神经末梢称为伤害感受器。它们向大脑发送能引起皮肤破裂的信号，如极端的高温或低温以及化学物质。

Another reason why paper cuts hurt so much is that you're using your hands throughout the day, meaning that the wound is constantly getting opened.

另一个导致伤口如此疼痛的原因是，我们整天使用双手，使伤口反复地裂开。

"You often get paper cuts on the pad or the tip of the finger, different from where you'd get a knife cut," said Dr Goldbach.

海莉医生说：“纸割破的伤口通常在指腹或指尖，这不同于刀割破的伤口。”

"It's hard not to use your hands, so there's constant pressure on the wound without a chance for it to heal."

“让双手休息也并非易事，因此，伤口持续受到压力，无法愈合。”

The paper itself is another reason why these superficial cuts leave us in so much pain.

纸张本身是皮肤割伤后巨疼的又一大原因。

Paper might look and seem smooth but, if you study it under a microscope, the edge is actually jagged. 

透过肉眼观看，纸张人畜无害，但透过显微镜发现，实际上纸张的边缘呈锯齿状。

"Paper is quite sharp, jagged — it's a bit of serrated edge," said Dr Goldbach. "It cuts you pretty quickly before you have the chance to realize it."

海莉医生说：“纸张十分锋利，边缘呈现锯齿状。在你尚未意识到之前，手指就已被割破。”

This, in turn, leaves behind a cut that is jagged rather than smooth.

因而，留下的伤口呈锯齿状，并不光滑平整。

Additionally, paper is made from wood pulp, cotton and other fibers, which can be left behind in the wound.

除此之外，纸张由木浆、棉花和其它纤维制成，这些纤维可残留在伤口里。

"Paper can contain fibers that are inflammatory, which is why it's important to run the cut under water and wash it with a little soap," said Dr Goldbach.

海莉说：“纸张里含有能引发炎症的纤维。因此，用水冲洗伤口，再用肥皂清洗是十分必要的。”

Additionally, paper cuts are quite shallow, which makes them even more annoying to deal with.

另外，伤口并不深，处理起来却更棘手。

When the body has a deep cut, blood clots to prevent bleeding and then a scab forms to protect it.

当身体的伤口很深时，血液凝固以止血，然后结痂保护伤口。

But paper creates cuts deep enough to reach the nociceptors but not deep enough to trigger the clotting mechanism, meaning it takes longer for new skin to replace the dead cells.  

但纸张割破的深度仅刺激了伤害感受器，并未触发凝血机制，导致皮肤细胞的新旧交替将会耗时更长。

Dr Goldbach added that there are mental and emotional elements that cause paper cuts to hurt more than other cuts.

海莉医生补充道，心理和情感因素也让人感觉，被纸割破的伤口比其它伤口更疼。

"There's the psychological element of surprise, that it happens so quickly that you don't have time to withdraw your hand," she said.

她说：“心理上出乎意料的因素也是原因之一。割伤来得如此之快，我们都来不缩手。”

"With some other injuries, you feel pressure so you have time to react."

“而我们对一些可预见的伤口会感到压力，从而有反应时间。”

She also added that because we don't expect to hurt ourselves while working with paper, the surprise of cuts leaves us in further pain. 

她还认为，因为我们不会想到会被纸划伤，所以这出乎意料的结果加剧了疼痛感。

"We tend to be careful with a knife — you're being careful on purpose because you know there's a danger," said Dr Goldbach.

海莉医生说：“我们往往会谨慎用刀，因为刀是危险品。”

While we're careful with knives, we're not so careful with paper. 

我们对刀有警惕心理，对纸张却没那般小心。

If you do get a paper cut, Dr Golbach recommends washing it with soap and water and putting a band-aid on it.

被纸张割伤时，海莉医生建议用肥皂和水清洗伤口，然后贴上创可贴。

"You want to make sure it's clean and covered to prevent re-traumatizing it," she said.

她说：“伤口一定要保持干净，全部包裹，以防再次受伤。” 

Dr Goldbach also suggests to not believe the old wives' tale that claims cuts heal faster if left uncovered because they form scabs.  

海莉医生也不赞成奶奶辈的偏方：敞开结痂的伤口，能加快愈合。

She says wounds that are kept moist under a bandage will be less painful and will replace the damaged skin cells more quickly with new ones.

她说，在创可贴下，伤口可保持湿度，能减少疼痛感，也能加速皮肤新细胞代替受损细胞。 

"Wounds like to be moist when they heal, it helps them heal quicker," she said. 

她说：“伤口愈合时喜湿，康复更快。”

Dr Goldbach added that paper cuts don't have high rates of infection — in fact, it happens so rarely that there are no available statistics — but warns that there are situations in which you should seek medical attention.  

海莉医生表明，纸张割破的伤口感染几率并不高。事实上，发生概率太低，甚至都无具体数据可寻。但她提醒，在一些情况下，还需寻求医疗护理。

"If it's red, if there's drainage, it looks contaminated or infected, see a doctor immediately," she warned. 

她提醒：“如果血流不止，伤口化脓，或有感染的症状，请立即就医。”