A listener from Ontario, California wrote to A Moment of Science with a question her sons had asked her.

 

　　The boys wondered why is it that when you get sunburned you often feel chilled. It really does seem like a contradiction: you’ve been burned, but you feel cold.

 

　　The answer to this seeming contradiction is in your blood.

 

　　Sunburn is an injury to your skin, and your body’s usual reaction to being injured is to enlarge the blood vessels in the damaged area. This allows more blood to be circulated near the injury, where it can deliver cells to help heal the wound.

 

　　Since sunburn is usually damage to the surface of your skin, the blood vessels in the area of the burned skin enlarge so that more blood is circulated there; this is where the redness comes from.

 

　　When you’re sunburned a large area of your body is usually involved, so a result of so much blood being near the surface of your skin is that you lose more than a normal amount of body heat through it.

 

　　Your brain tries to balance this loss of heat by activating reactions which attempt to conserve heat. A common reaction is shivering, which is the body trying to generate heat in an effort to compensate for the heat that is being lost.

 

　　So, even when your skin feels hot to the touch, you shiver and feel chilled as your body tries to make up for the extra heat loss.

 

　　寒冷的晒伤！

 

　　一名来自加利福尼亚安大略的听众给我们写信，让我们解答她儿子们问她的问题。

 

　　这些小男孩想知道为什么人晒伤的时候会觉得冷。这简直就是自相矛盾嘛。你明明晒伤了，却觉得冷。

 

　　这个看上去自相矛盾的问题的答案就在你的血液当中。

 

　　晒伤表明你的皮肤受到了损伤，而通常人体应对损伤的办法就是使受创位的血管扩张。这使得更多的血液在伤口附近循环，同时血液中的一些细胞也会被输送到伤口附近，帮助伤口愈合。

 

　　由于晒伤通常会损害你的皮肤表面，而晒伤部位的血管会扩张，使更多的血液在附近循环。这就是为什么晒伤部位会变红。

 

　　晒伤通常会波及到人体的大部分区域。而大量血液聚集在皮肤表面附近的结果就是：你会散失比平时更多的热量。

 

　　为了平衡损失，大脑尝试通过刺激人体作出某种反应来保存热量。该反应通常表现为颤抖，颤抖表明人体正试图产生热量来补充正在散失的那一部分。

 

　　因此，即使你的皮肤摸一下都觉得发烫，但你还是会颤抖，觉得冷，因为这时人体正设法补充额外散失的热量。