Why can millions of hairs grow from our heads, and yet our palms and the soles of our feet are as bare as anything? It all comes down to a special molecule¹ in our bodies, according to the scientists who have found it.

为什么数以百万计的头发可以从我们的头上长出来，而我们的手掌和脚底却是光秃秃的？据发现这一问题的科学家表示，一切都归结于我们体内的一种特殊分子。

The hairless regions of our skin secrete² a special type of molecule known as an inhibitor. This particular one is a protein named Dickkopf 2 (DKK2). These effectively brick-up the WNT pathway, which is in charge of triggering hair growth in our bodies.

我们皮肤的无毛区域分泌一种特殊的分子，称为抑制剂。这种特殊的蛋白质叫做Dickkopf 2(DKK2)。这些物质有效地堵塞了WNT通路，而WNT通路负责刺激我们体内的毛发生长。

Scientists at the University of Pennsylvania School of Medicine believe certain animals have evolved to produce DKK2 in certain parts of their bodies, depending on what will best help different creatures to survive.

宾夕法尼亚大学医学院的科学家们认为，某些动物已经进化到在身体的某些部位产生DKK2，这取决于哪种物质最有助于不同的生物生存。

"In this study, we've shown the skin in hairless regions naturally produces an inhibitor that stops WNT from doing its job," Professor Sarah E. Millar, an author of the study published in the journal Cell Reports, commented.

这项研究的作者萨拉·E·米勒教授评论说：“在这项研究中，我们已经表明，无毛区域的皮肤自然会产生一种阻止WNT发挥作用的抑制剂。”

为什么有些地方长毛发有些地方却不长?

Millar, who is a professor in dermatology at the University of Pennsylvania School of Medicine, continued: "We know that WNT signaling is critical for the development of hair follicles; blocking it causes hairless skin, and switching it on causes formation of more hair."

米勒是宾夕法尼亚大学医学院皮肤学教授，他接着说：“我们知道WNT信号对毛囊的发育至关重要；阻断它会导致无毛的皮肤，而开启它会导致更多毛发的形成。”

For their study, the researchers analyzed³ mouse skin similar to that on a human wrist. Their work showed the protein DKK2 was expressed highly in this part of the mammal compared to hairy areas.

在他们的研究中，研究人员分析了老鼠与人类手腕相似的皮肤。他们的工作表明，与毛发区相比，这部分哺乳动物体内的DKK2蛋白表达量较高。

As with mice, humans don't grow hair in their wrist area, whereas other mammals, like rabbits and polar bears, do, the authors highlighted. When they compared DKK2 expression in mouse wrist skin with rabbit, they found it in lower levels in the latter.

研究人员强调，与老鼠一样，人类手腕部位的毛发不会生长，而兔子和北极熊等其他哺乳动物会。他们将小鼠腕部皮肤的DKK2表达与兔腕部皮肤的DKK2表达进行比较，发现兔腕部皮肤的DKK2表达较低。

"WNT is still present in hairless regions, it's just being blocked," explained Millar.

米勒解释说：“WNT仍然存在于无毛地区，只是被阻挡了。”

The team hopes its findings could help prompt further research into hair growth. This could, in turn, lead to treatments in those where the body has stopped producing hair in particular areas, for instance those with deep wounds or burns, Millar said.

研究小组希望这一发现能有助于进一步研究头发的生长。米勒称，这进而可能导致在身体某些特定部位停止长头发的人，比如那些有深度伤口或烧伤的人，得到治疗。

"We hope that these lines of investigation⁴ will reveal new ways to improve wound healing and hair growth, and we plan to continue to pursue these goals moving forward," Millar said.

米勒表示：“我们希望这些研究将揭示改善伤口愈合和头发生长的新方法，我们计划继续追求这些目标。”