Why bald people don’t get goose bumps on their scalp

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New research has uncovered an important function of the tiny muscles, called arrector pili, that cause goose bumps: healing and cell regeneration.

The work could lead to new treatments for burn victims, prevention of skin cancer, and even a solution for baldness.

Goosebumps are very small elevations in the skin that occur around the hair follicle. On the side wall of every follicle, under the surface of the skin, lies the goose bump muscle. When hair emerges from the skin, it usually sits at an angle. When the goose bump muscle contracts, it elevates the hair and pulls the angle of the follicle straighter so the hair literally stands on end.

In mammals, goose bumps provide protection against the cold by creating an air pocket that seals warm air around the follicle to create a layer of insulation.

They can also be activated by adrenalin, which floods through the body in response to a threat. For fluffy creatures, hairs standing on end make them appear bigger. Strong emotions can also cause adrenalin to be released, which is why we get goose bumps in response to music we love, or a strong memory.

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Some people experience goose bumps more than others based on how much hair they have or their tendency to panic. Very rarely goose bumps can form tumors or become inflamed, but they usually cause no problems.

Professor Rodney Sinclair, head of dermatology at the University of Melbourne, says that for us “naked apes,” goose bumps are often thought of as a kind of evolutionary hangover.

“People used to think the goosebump muscle was vestigial—an evolutionary remnant of no functional significance. The research we’ve done has involved doing 3D constructions of this muscle and it was a lot more interesting than we thought.”

Humans have two million hair follicles, only 100,000 on the scalp. Many of our hairs are tiny vellus hairs that don’t produce significant coverage. But humans no longer need hair for warmth, because we wear clothes. Nor do we need to blow up into a puffy hairball to scare off our enemies.

So why do we still get them? It has to do with maintaining vital stem cells of the skin.

Hair follicles have the unique ability to completely regenerate. When a hair is plucked, up to 70 percent of the follicle is destroyed, but when the hair regrows, the follicle regenerates itself.

The lower end of the goosebump muscle is attached to the follicle, so it creates a “stem cell niche”—a place that protects and maintains stem cell populations. The upper end of the goose bump muscle creates a second stem cell niche, which is even more important because it maintains the stem cell population for the entire outer layer of the skin. The muscle is like a dumbbell connecting the two vital stem cell niches.

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“When you graze your knee, a signal is transmitted to the damaged hair follicle that there is a deficiency in the surface skin cells,” explains Sinclair. “The hair follicle stem cell is activated and skin cells are produced that are then sent up to the surface to heal the graze.

“Until we did this research, no one knew where the stem cells were in the epidermis. The stem cell population are very important in wound healing and skin cancer.”

This is big news for the one million skin cancer patients who receive treatment every year and particularly significant in Australia, where seven out of eight cancer diagnoses are skin cancer.

“Knowing where the stem cells are is really important. If you’re going to develop a new treatment for skin cancer, it has to be directed to where the mutations in the skin cells are leading to cancer. We know the stem cells pass the mutation on to the daughter cells which leads to skin cancer,” says Sinclair, whose work appears in the journal Anatomical Science International.

“The other role is in maintenance of the epidermis—epidermal homeostasis. Every time you rub your skin, dead skin cells are shed off the surface, meanwhile new skin is dividing in the skin cells.

“One of the problems in trying to grow new skin for burn victims is that they have a depleted skin population and the skin is not functioning properly.”

The goose bump muscle could also impact something else of interest to millions worldwide: baldness.

“We discovered this year that when you go bald, part of the problem is because the attachment of the goose bump muscle to the hair follicle is destroyed and replaced by fat,” says Sinclair. “You can’t get goose bumps on the scalp when you go bald and you can’t regrow hairs either because the follicles can’t regenerate.”

Finding a solution to why the goose bump muscle is destroyed may provide more advances in treating baldness, which affects many millions worldwide.

Source: University of Melbourne