Hair plays a pivotal role in culture. More than just a visual marker of your personal grooming habits, the way you wear your hair (facial, scalp, and otherwise) can say a lot about your religion, your job, your politics. It can be a status symbol. It can dictate whether people see you as ditzy or fiesty, and its loss is a cultural shorthand for midlife crises. Here are 23 things you might not know about the stuff that grows out of your head (and on your face and the whole rest of your body) from Hair: A Human History, a new book by skin biologist and longtime hair researcher Kurt Stenn.

1. GOOSEBUMPS ARE A VESTIGE OF OUR HAIRY PAST.

In animals, hair follicles stand up to make the fur thicker, creating better insulation. But because human body hair isn’t thick or dense enough, it becomes a pretty useless involuntary response.

2. BEING (RELATIVELY) HAIRLESS IS IMPORTANT FOR HUMAN MOBILITY.

On a 104°F day, an upright hominid in Africa would have a heat stroke after walking for just 10 to 20 minutes. Being (relatively) hairless allowed us to dissipate the heat human ancestors generated moving around. Being able to keep cool, in turn, supports humans’ large brains, since brain tissue is very heat-sensitive.

3. JULIUS CAESAR HAD A COMB OVER.

“His baldness was a disfigurement which troubled him greatly,” as Stenn quotes from the history The Lives of the Twelve Caesars, “since he found that it was often the subject of the gibes of his detractors. Because of it he used to comb forward his scanty locks from the crown of his head.”

4. MILITARY HAIRCUTS DATE BACK TO ALEXANDER THE GREAT.

Alexander mandated short hair for all his soldiers, since long hair could easily be grabbed in hand-to-hand combat. In contemporary life, we still associate buzz cuts with order and discipline. It’s no coincidence that peace-loving American hippies chose to grow their hair long in the 1960s.

5. MEDIEVAL BARBERS WERE SURGEONS, TOO.

After a 13th century decree banned monks from doing surgery, barbers did the basic medical work like lancing abscesses, extracting teeth, bloodletting, and more. They knew how to use a blade, after all. It wasn’t until 1745 that England’s professional organization for barbers and surgeons split into the separate Company of Surgeons and Company of Barbers. From this tradition, we got the barber’s pole, which was initially a bandage-wrapped pole that patients gripped during bloodletting procedures.

6. CUTTING HAIR WAS A RARE PATH TO WEALTH FOR AMERICAN SLAVES. 

Plantation owners kept some of their slaves as personal servants, responsible for making sure the master looked good. Slaves who were particularly good barbers were sometimes allowed to set up shops in cities, and some slave barbers earned enough money to buy themselves and their families out of bondage. Because of plantation culture, people associated barbering with slavery, and the trade was disproportionately African American. In the late 1800s, 96 percent of Charleston’s barbers were African American.

7. GILLETTE KILLED THE BARBER SHOP. 

King Gillette, a traveling salesman, invented the safety razor. Because it was much easier to use than a straight razor, people could now shave at home, and didn’t need to go to the barbershop every day or few days. 

8. THE CURLING IRON LAUNCHED WOMEN'S HAIR SALONS. 

Image Credit:State Library of New South Wales via Wikimedia Commons// Public Domain

Marcel Grateau groomed horses before he set up shop as a ladies’ hairstylist in Paris. He invented a new way to curl hair (the curling iron) and gave birth to the Marcel wave—that recognizable flat wave of the flapper era. His success legitimized the new notion of a public hair salon for women.

9. COWLICKS CAN REFLECT HANDEDNESS. 

A survey of 500 North Americans found that 90 percent of right-handed people had a cowlick whorl that grew clockwise. Left-handed and ambidextrous individuals weren’t associated with a particular direction of whorl.

10. YOU HAVE A TON OF HAIR. 

Humans have about 100,000 follicles on their scalp and between 3 and 5 million all over the body. 

11. HAIR IS STRONG. 

A single scalp hair can lift about a quarter pound of weight without breaking. To pull a scalp hair out from the root, it takes about a fifth of a pound of force.

12. HAIR FOLLICLES HAVE LONG MEMORIES.

Hair follicles transplanted to other parts of the body will continue growing the same type of hair they always have. So a hair follicle from the scalp transplanted onto the eyebrow will grow long like head hair rather than short like eyebrow hair.

13. ANIMAL HAIR IS SUPER DENSE.

A piece of beaver skin the size of a fingertip has 40,000 hair shafts. It’s so dense it’s water- and wind-proof. On the flip side, that’s why furry animals don’t sweat: the water under their fur wouldn’t be able to evaporate. 

14. YOU LOSE DOZENS OF HAIRS A DAY.

Around 50 to 100 hairs fall out of your scalp every day. Scientists aren’t quite sure why hair follows a cycle of forming, falling out, and reforming. Hair follicles are some of the only human organs that cycle like this besides the uterine lining. 

15. STRESS AFFECTS YOUR FOLLICLES. 

Nerves transmit stress signals to hair follicles, causing hair growth to slow down. However, injuries like cuts seem to actually speed up hair growth.

16. HAIR FOLLICLES DON’T KNOW WHEN YOU GET A HAIR CUT.

Your hair is really a stack of dead cells. Your “hair shaft cells are essentially fossilized,” Stenn writes. Thus, you can’t feel it when your hair gets cut. Nor does it send a signal to your hair follicles. Pulling hair out by the root alerts the follicles to grow again, but cutting does not.

17. BALD HEADS AREN’T TOTALLY HAIRLESS. 

As someone balds, their follicles and hair shafts get smaller and smaller until they’re only visible with a microscope.

18. BALDNESS IS LINKED TO FOXES, AT LEAST LINGUISTICALLY.

Alopecia, the medical term for hair loss, comes from the Greek word for fox, alopex. In ancient Greece, people associated human hair loss with that of mange-ridden foxes.

19. HAIR NEEDS A PROTEIN-RICH DIET. 

To produce fine merino wool, sheep must eat at least 9 pounds of pasture per day, yielding 3.5 ounces of protein or more. No wonder they spend so much time grazing. 

20. CONDITIONER CHANGES THE CHARGE OF YOUR HAIR.

Conditioner coats the hair in molecules that give the shaft a positive charge. Because a positive charge repels another positive charge, hairs are less likely to knot together.

21. HAIR CAN BE USED TO RETRACE HISTORY.

Hair grows about half an inch per month as cells are added to the base of the shaft. In 2007, hair was used to solve a sexual assault case. Around a month after a 19-year-old woman reported waking up from a party thinking she may have been drugged, a forensic pathologist tested her hair and found traces of ketamine around 1 inch from her scalp, about where the base of her hair would have been one month prior. The accused confessed to the crime after this evidence was presented.

22. HAIR CAN SOAK UP OIL SPILLS.

A protestor holds a hair boom in the air after the BP Deepwater Horizon oil spill in 2010. Image Credit: Infrogmation via Wikimedia Commons // CC BY 3.0

Naturally, hair is covered in sebum, an oil from the sebaceous glands. After the 1989 Exxon Valdez oil spill, an Alabama hair dresser realized that hair must be able to soak up other oils, too. He tested untreated hair from the floor of his salon with motor oil and water, discovering it to be an effective cleaning agent. Hair mats were used to clean up an oil spill in the San Francisco Bay in 2007. However, BP declined hair donations collected for its Gulf of Mexico oil spill in 2010, saying the hair booms made for oil spills are absorbent, but can be difficult to use and dispose of.

23. SCIENTISTS CAN PROGRAM HAIR TO FALL OUT.

Some sheep farms inject their herds with a protein growth factor that makes hair shafts break off, so fleece peels right off the animal, no shearing required.

All images from iStock unless otherwise noted.