Why Humans Don’t Have Hair on Some Body Parts

Compared with most other mammals, humans are absolutely naked, except for long hair, which has only a few furry fluff.

It is obviously strange that our palms and feet are smooth and hairless. Unlike rabbits and polar bears, they also have hair on their paw pads.

Although there are still other doubts, the researchers are likely to have found the answer.

A new study reveals a very important molecular pathway that makes our palms and feet feel as smooth as baby skin. The protagonist is a molecular messenger called the Wnt signaling protein, which carries information about the growth of body hair.

The study’s lead author, Sarah Millar, a dermatologist from the University of Pennsylvania, said: “Wnt signaling protein plays an important role in the development of hair follicles. If it stops working, the skin is hairless. If it is activated, the hair will grow. In this new study, we found that skin in the hairless area produces an inhibitor that prevents Wnt from functioning.”

The inhibitor is a protein called Dickkopf 2 (DKK2). When the researchers extracted all the DKK2 from the mice, something strange happened: they had small hairs on their bare paws.

Normally normal mice have no hair on their soles, but in 40 experimental mice, the researchers found that mature hair follicles that had been fully formed appeared on the soles of mice. Even if the hairs on their soles are pulled out, they will grow back again, just like other areas where hair is usually present.

When the researchers turned their attention to the rabbit, they found a similar situation.

DKK2 seems to play a role in it, or that the lack of DKK2 has played a role. In the skin of the soles of rabbits, the researchers found that the expression level of DKK2 is not high, which may be the reason for the fluff of the rabbit’s sole.

This result is beyond the expectations of the researchers. At first, they thought that DKK2 may be related to the formation of hair follicle morphology in the body, but found that the opposite is true, DKK2 inhibited the formation of hair follicles.

Researchers now believe that it is the presence of DKK2 that causes individual parts of the body to have no hair. Therefore, when the researchers removed the inhibitor, the Wnt signaling pathway began to work, activating beta-catenin, and the hair follicles began to grow on the soles of the palms.

As for why humans have evolved to the point where the palms of the hands are bare, there is still no answer, but there are several assumptions.

Some people think that it is related to sexual choice (the cost of gender); it is said to be related to thermoregulation, because human ancestors migrated from the forest to the sun-drenched prairie; others believe that less hair helps protect us from external parasites.

But no matter which explanation is correct, if we can extend the findings of this research to humans, then we don’t have to worry about our own volume!

The treatment of hair growth is very useful for a variety of health problems, such as dealing with male pattern baldness, so that their heads are no longer bright, or treating skin problems such as fresh skin and helping to treat burn patients.

Although we still need more research to deepen our understanding of Wnt and DKK2, the results of this study suggest that drugs that reduce Wnt/β-catenin levels in the skin may prevent hair from becoming too strong; conversely, if safe A controlled way to activate Wnt will help hair follicle growth and solve baldness problems.


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