Goosebumps are a weird quirk of our bodies that science doesn’t fully understand. Now, researchers at Harvard have uncovered a biological reason for the reaction: it’s our bodies’ way of stimulating stem cells to drive new hair growth.
We’re all familiar with goosebumps. When you’re cold, your skin prickles with tiny bumps and your hair stands on end. But why does it happen? One of the leading theories is that it’s a holdover from our primitive past, when we were much hairier than we are today. Back then, the hair-raising reaction would have helped warm us up.
But since it doesn’t really help our mostly hairless selves now, scientists have wondered why it persists today when evolution should have filtered it out long ago. So for the new study, the Harvard team investigated what’s going on at the cellular level, to figure out what other benefits it may be delivering.
In tests in mice, the researchers found a potential purpose. The cells that cause goosebumps, it turns out, also play a key role in regulating the stem cells that regenerate the hair and hair follicle. This effect was boosted when the cold temperatures were prolonged. That means that goosebumps are essentially a short-term solution, while the body tries to stimulate new hair growth to keep us warmer over the long term.
“This particular reaction is helpful for coupling tissue regeneration with changes in the outside world, such as temperature,” says Yulia Shwartz, co-first author of the study. “It’s a two-layer response: goosebumps are a quick way to provide some sort of relief in the short term. But when the cold lasts, this becomes a nice mechanism for the stem cells to know it’s maybe time to regenerate new hair coat.”
The general cellular mechanism behind goosebumps has long been known. When it gets cold, the sympathetic nerve contracts a tiny muscle that connects to the bottom of a hair follicle. This pulls it tight, causing the hair to stand on end. It also causes the skin around the hair to pull inwards, which is what creates the bumpy texture that gives it its name.
But the team discovered a new part of this equation. Examining the skin using electron microscopy, they found that the sympathetic nerve also has a direct connection to the hair follicle stem cells, wrapping around them. When the nerve is activated, it also activates the stem cells to begin growing new hair.
“We could really see at an ultrastructure level how the nerve and the stem cell interact,” says Ya-Chieh Hsu, co-lead author of the study. “Neurons tend to regulate excitable cells, like other neurons or muscle with synapses. But we were surprised to find that they form similar synapse-like structures with an epithelial stem cell, which is not a very typical target for neurons.”
The researchers plan to continue exploring how else the external environment affects the stem cells in the skin.
The research was published in the journal Cell.
Source: Harvard