For most people, summer involves numerous daily shifts between scorching outdoor heat and frosty air-conditioned interiors. But does exposing the body to extreme temperature swings make people sick? Professor Ron Eccles, director of the Common Cold Centre at Cardiff University in Wales, which performs clinical trials for treatments for coughs, colds and flu, explains why keeping a sweater at work isn't such a bad idea.

对大多数人而言，夏季每天要在高温酷热的室外与“寒冷”的空调房之间转换无数次。但人体暴露于巨大的温度变化中会让人生病吗？威尔士卡迪夫大学(Cardiff University in Wales)普通感冒中心负责人、教授埃克尔斯(Ron Eccles)解释了为何在办公室中放一件套衫并不是个坏主意。该中心为咳嗽、感冒和流感疗法进行临床试验。

 

Chill Defenders

御寒机制

 

As warm-blooded animals, humans are hard-wired to keep our body temperature at around 98 degrees Fahrenheit. So when a person is exposed to frigid environments after being in the summer heat, the body 'will do whatever it can to defend itself against chilling,' Prof. Eccles says.

作为恒温动物，人类体温恒定地保持在36.7摄氏度左右。埃克尔斯说，因此，当人在夏季的酷热中待了一段时间后，接着进入寒冷的环境，人体会尽一切努力为自己御寒。

 

One such defense: A thermal regulator in the brain, after receiving messages from temperature sensors in the skin, automatically alerts blood vessels there to constrict. 'You can see this when someone suddenly goes into a very cold building, they go pale or their skin mottles,' says Prof. Eccles. The next stage is shivering, which will raise body temperature by generating heat.

其中一种御寒机制是：大脑中有一个温度调节系统，在接收到皮肤中的温度传感器发来的信息后，温度调节系统会自动提醒皮肤血管收缩。埃克尔斯说，有的人突然进入一座非常冷的楼里时，他们会面色发白或皮肤起斑点，原因就在于此。接下来就是打冷颤，打冷颤可以产生热量，进而提高体温。

 

At the same time, blood vessels constrict in the nose and throat, where bacteria and viruses often lurk. 'If you were to look into a throat, you could see it go from a nice pink-red to a very pale color,' says Prof. Eccles. 'This happens within a few seconds to conserve the heat that we lose to the air we breathe out.'

与此同时，鼻子和喉咙——这里是细菌和病毒常常潜伏的地方——的血管收缩。埃克尔斯说，如果检查一下喉咙，你会发现喉咙从正常的粉红色变成一种非常灰白的颜色。这种变化在几秒钟内就会发生，以便减少我们呼出的空气带走的热量。

 

Immunity in Retreat

免疫系统减弱

 

When blood flow diminishes, the white blood cells that typically fight bacteria and viruses do too, allowing these latent risk factors to easily bloom into a full-blown cold. 'If there isn't as much blood flow to the throat, there aren't enough white blood cells to ward off infection,' Prof. Eccles says.

血流减少时，抗击细菌和病毒的白血球也会随之减少，潜在的风险因素就容易发展成为感冒。埃克尔斯说，如果喉咙的血流减少，就没有足够多的白血球来预防感染。

 

But, he emphasizes, a cold won't develop unless the bacteria or virus is already present in the body.

但他强调说，除非人体内已经有细菌或病毒，否则不会发展成为感冒。

 

The Sweat Factor

汗的因素

 

Sweating can amplify the risk by keeping the body colder longer-and making it harder to regain an optimal core temperature. Having sweaty clothes when walking into an air-conditioned building 'could feel like diving into an ice-cold swimming pool,' says Professor Eccles.

出汗会使人体更长时间地保持在寒冷状态，使人体更难恢复理想的体温，进而可能增大感冒的风险。埃克尔斯说，如果穿着汗湿的衣服走进空调房，感觉就像跳进冰冷的泳池一样。

 

Getting some of that perspiration to evaporate first, by sitting in the shade for a few moments, for example, can help. So can keeping a sweater or light jacket at the office to ease the temperature transition.

先消消汗可能有所帮助，比如可以在阴凉地里坐一会。在办公室里放一件套衫或薄外套，延长温度变化的过程，这样做也有帮助。

 

Heating Up

由冷到热

 

Heading in the other direction-from the deep freeze to the steamy outside-doesn't pose the same cold risk, says Prof. Eccles, since even more blood circulates to the skin, nose and throat. 'It's a lot like when your car radiator goes on when it gets too hot, to cool off,' he says. 'If you're very overheated, much of your five liters of blood gets distributed to the skin-turning you red-to eliminate heat.'

埃克尔斯说，反之，从极冷的室内走到蒸笼一样的室外不会带来同样的感冒风险，因为从冷的环境到热的环境，皮肤、鼻子和喉咙的血液循环会加快。就像太热的时候，你汽车里的散热器就会启动来降温一样，如果你热过了头，你体内的五升血液大部分会流向皮肤来散热，你的皮肤会发红。

 

It can take the body only a few seconds or minutes to acclimate to the cold inside, says Prof. Eccles.

埃克尔斯说，人体适应室内的低温通常需要几秒钟到几分钟的时间。

 

'Every time you go outside, you're going to go through the chilling again' when you return, he says. If you have to step out from the chill into the heat frequently, he says, 'limit your time to a few minutes.' This way, your body won't have time to fully adjust to the heat-and the cycle won't start again.

他说，每次出去后再回来，你都会再次经历冷却的过程。他说，如果你需要经常从室内到室外，那么就将时间限制在几分钟内。这样，你的身体就不会有时间完全适应室外的高温，这样你再进入室内时也就不会启动这个循环过程了。