A new study provides scientific evidence to support the idea that stress can cause a person's hair to turn gray.
A team from America's Harvard University said the new study is the first to show a clear link between stress and graying hair. The findings were recently published in the journal Nature.
Researchers say they discovered a chemical process that can change hair color during times of stress. The process is linked to the body's "fight-or-flight" reaction that can happen during dangerous situations.
Ya-Chieh Hsu is a professor of Stem Cell and Regenerative Biology at Harvard. She said in a statement that the research team was in search of the first scientific confirmation of the commonly held belief that stress can cause gray hair. Everyone has an anecdote to share about how stress affects their body, particularly in their skin and hair - the only tissues we can see from the outside, Hsu said.
The team used experiments with mice to look at how stress affects stem cells in hair follicles. Most people have about 100,000 hair follicles on their head. The follicles are responsible for making melanocytes, the cells that give hair its color. As people age, melanocyte production is reduced. This causes a person's hair to begin turning gray naturally.
At first, the researchers suspected that an immune attack caused by a stressful event might be targeting the melanocyte stem cells. That theory, however, turned out to be false. The mice lacking immune cells still showed signs of graying hair.
The team also thought the hormone cortisol, which always increases in the body during times of stress, might be a likely cause. However, when researchers removed the gland that produces the cortisol hormones, the hair of mice still turned gray.
The scientists then centered their experiments on the body's sympathetic nervous system. This is the body system that controls "fight-or-flight" reactions in dangerous situations.
The sympathetic nervous system is made up of a collection of nerves that extend through the body, including the skin. When the mice were subjected to short-term pain or placed in stressful laboratory conditions, these nerves released a chemical called norepinephrine. The chemical then flowed through the stem cells up into the hair follicles -- where melanocytes are kept.
The researchers found that when the norepinephrine was released, all the melanocyte stem cells were highly activated and changed into pigment-producing cells. This overproduction process resulted in the early loss of color-producing cells.
1.in search of 搜寻，寻找
The scientists are in search of a new element.
2.be responsible for 对……负责
He should be responsible for that.
来自美国哈佛大学的一个团队称，这项新研究是首个表明压力和头发变灰之间存在明显关联的研究 。研究的发现成果最近发表在了《自然》期刊上 。
研究人员表示他们发现了一个化学进程，这个进程可以在人处于压力期间头发会改变颜色 。这个进程与人体“战斗还是逃跑”的反应机制有关，这个反应机制会在危险的情况下发生 。
Ya-Chieh Hsu是哈佛干细胞与再生生物学的教授 。她在一份声明中表示，该研究团队在寻找对一种常见想法的科学验证，这个常见想法是——压力会导致头发变灰 。关于压力如何影响自己的身体，尤其是如何影响皮肤和头发，每个人都会有点儿奇闻异事要说——皮肤和头发是外在能看到的变化，这位教授这样说道 。
该团队通过小鼠实验来观测压力是如何影响头发毛囊的干细胞的 。大多数人头部有近10万个毛囊 。毛囊是负责制造生黑色素细胞的，而生黑色素细胞可以影响头发的颜色 。随着人年龄的增长，生黑色素细胞的生成量会减少 。所以人的头发会自然变灰 。
起初，这些研究人员怀疑压力事件引发的免疫攻击可能会攻击黑素干细胞 。不过，这个理论证明是错的 。缺少免疫细胞的小鼠有出现灰发的迹象 。
该团队还考虑了荷尔蒙皮质醇，荷尔蒙皮质醇会在人处于压力时增加在体内的含量，这是一个可能的诱因 。不过，当研究人员移除了产生皮质醇激素的腺体之后，小鼠的头发变灰了 。
然后，科学家将实验聚焦到了身体的交感神经系统上 。交感神经系统控制着人体自危险情况下的“战斗还是逃跑”反应 。
交感神经系统由遍布身体的神经组成，包括皮肤 。当小鼠处于短期疼痛下或者处于实验室的压力环境中时，小鼠的神经会释放一种叫做去甲肾上腺素的化学物质 。然后，这种化学物质会流过干细胞，流至头发的皮囊——生黑色素细胞就得以保留 。
这些科学家发现，当去甲肾上腺素释放的时候，所有黑素干细胞都处于高度激活状态，会变成产生色素的细胞 。这个产生过量的过程会导致产生颜色细胞的过早流失 。