Why do humans have body hair?

Announcer: Welcome to Stuff You Should Know from HowStuffWorks.com.

Josh Clark: Hey, and welcome to the podcast. I'm Josh Clark. Chuck Bryant, how you doing, man?

Chuck Bryant: I am well. That sounded very unsure.

Josh Clark: I'm feeling the same way. Is it Chuck and I recording on a Monday? Jerry is forcing us to. Usually, we record on Fridays. It's the last thing we do in the week, which is we're so chipper and up and drunk. And you know, this is a shift! It's different.

Chuck Bryant: Yeah, it's like a funeral.

Josh Clark: It's harshing our buzz.

Chuck Bryant: Plus, it's kind of cloudy out, and the weather affects me. I have SAD. Seasonal affective disorder!

Josh Clark: Do you really?

Chuck Bryant: Yeah, a little bit.

Josh Clark: Like diagnosed?

Chuck Bryant: No. Self-diagnosed!

Josh Clark: Are you also self-medicating?

Chuck Bryant: No, I'm not into that.

Josh Clark: Good for you, Chuck. All right, well, I have a question for you.

Chuck Bryant: Fire away.

Josh Clark: Did you ever, when you were a kid, did you have one of those plastic shavers, little razors?

Chuck Bryant: Yes.

Josh Clark: Did you? Did you use it, or did you just leave it around?

Chuck Bryant: Yeah, I remember getting into my dad's shave cream and playing around like I had facial hair.

Josh Clark: Me too.

Chuck Bryant: And now we do have facial hair.

Josh Clark: I know. It's kind of like when I was a kid, when I was like seven, all I wanted to do was mow the lawn more than anything else. And then come eight, I actually got to mow the lawn. And the first three times were heaven. Then after that, I was like, "You are such a chump." Same thing with shaving. It was like really exciting, and now it's things just get kind of mundane after you do them a number of times.

Chuck Bryant: Yeah, I was pretty late to the - a late bloomer to the facial hair, too. So later on in high school, my friend Jim that you've met, he is of Arabic descent, and Jim literally had a mustache when he was in the eighth grade. It was one of those thin ones, and he's a drummer in a band. And so he had the little mullet and the mustache.

Josh Clark: Yeah, I knew a kid like that, too. His name was Ron. He was of Polish descent. And his voice was deep in the third grade, and his stache started coming around a little after that.

Chuck Bryant: Yeah, I developed a little later. I'm still developing.

Josh Clark: Are you?

Chuck Bryant: Yeah.

Josh Clark: Your voice is still changing. Isn't it?

Chuck Bryant: It is.

Josh Clark: Very nice, Chuck. Sexy! Have you ever wondered, though, why - how about this for a segue? Have you ever wondered, Chuck, why humans even have body hair?

Chuck Bryant: I hadn't until I read this article, and then it kind of occurred to me, "Yeah, that's kind of weird. Why do we have hair?"

Josh Clark: This isn't the first time I've thought of this.

Chuck Bryant: Really?

Josh Clark: Yeah.

Chuck Bryant: Did you think that when you were a little kid?

Josh Clark: No, anthropology student.

Chuck Bryant: Yeah, I wasn't down with anthropology.

Josh Clark: Remember when we were just talking about shaving the face? Did you know that you or I will probably spend about a month out of our lives shaving?

Chuck Bryant: I'll probably spend less than that, but yeah, I'm below average. I shave once a week.

Josh Clark: I am, too. I shave once a week, too. God, we are made for each other. Aren't we? Wow. Well, let's get to this. All right?

Chuck Bryant: Yes. Humans have hair.

Josh Clark: Why does your hair grow - the hair on your head grow longer than the hair on your arms? Chuck Bryant.

Chuck Bryant: Well, before we go there, Josh, we need to understand a little bit about hair. Can we go there? What happens is when you're talking hair growth; you have cells inside the hair follicles. They divide and they multiply, and then space fills up inside the follicle, and it pushes older cells out.

Josh Clark: Right because hair is actually just like the protein keratin and dead cells that have hardened.

Chuck Bryant: Right, that sounds kind of gnarly when you put it like that.

Josh Clark: Did you know that something like 98 percent of all dust is dead skin cells?

Chuck Bryant: Ew, really? Yuck. That's like bed bugs. Not to get off on another tangent, but all that stuff grosses me out. Never bring a black light into a hotel room. That's all I have to say. So as space fills up, it pushes the older cells out, like I was saying and those cells harden and exit the follicle and forms a hair shaft, which you said is mostly dead tissue and keratin. Correct?

Josh Clark: Yes.

Chuck Bryant: So that's basically what's going on. But it happens in spurts. It rests, and it - active and resting phases.

Josh Clark: So the active phase - the growth phase is called the anagen phase, and then there's the telogen phase. And those are resting phases. And strangely enough, different parts of your body go through different phases at different times.

Chuck Bryant: Right, which is what you're talking about with the arm and the head?

Josh Clark: Right. So your arm hair has much longer telogen or resting phases than your hair head - your head hair, which I usually just call hair, which is why this is going to be a really confusing podcast.

Chuck Bryant: I know because there's different types of hair on different parts of your body.

Josh Clark: Yeah, let's caveat that right now. If we just say hair, we're talking about the head, the scalp. Everything else is facial hair, arm hair. You know, there's a qualifier.

Chuck Bryant: But let's go ahead and get the different types of hair out of the way. What you have in the womb are little tiny hairs called lanugo.

Josh Clark: That's how I pronounced it, too.

Chuck Bryant: Then after you're born, babies grow vellus, which is fine, unpigmented hair across your body.

Josh Clark: It's like peach fuzz.

Chuck Bryant: Yeah, little baby's heads are all soft.

Josh Clark: They're so cute.

Chuck Bryant: They are. And then you hit puberty, most of us, and the vellus hairs give way to terminal hairs, and they're a little more coarse. And that's what you find underneath your armpits and around your genital area.

Josh Clark: Or on my back and shoulders.

Chuck Bryant: On your back, sure. Do you have a hairy back?

Josh Clark: Holy cow.

Chuck Bryant: Really?

Josh Clark: Yeah.

Chuck Bryant: I didn't know. I've never seen you with your shirt off.

Josh Clark: I'm like a Class 4 or Robin Williams level of hairy.

Chuck Bryant: Wow.

Josh Clark: I'm not quite there. It's up there.

Chuck Bryant: Yeah, I'm not that bad. I have the creepers that come around the collar, but Emily waxes me from time to time.

Josh Clark: Does she?

Chuck Bryant: Yeah.

Josh Clark: My brother in law is shaved by my sister down to where the collar of his undershirt comes, and if you ever see him with his shirt off, it's like hair, no hair. It's really hilarious.

Chuck Bryant: It's like the redneck tan.

Josh Clark: Kind of, yeah.

Chuck Bryant: That's nice. So then back to the hair that we all think about, the hair on the scalp, the thicker hair, eyebrows, eye lashes. That's also terminal hair, which is the same as what a lot of people call pubic hair. It's actually the same type of hair. You might not think so, but it is. It's terminal.

Josh Clark: Okay, so and then a different kind of hair - this is distribution. Not the type of hair is androgenic, and that's like your facial hair, your chest hair, your arm hair. And it's usually stimulated by the hormone testosterone.

Chuck Bryant: Right. And then you add all that up together, Josh, and you get about 5 million individual hairs for an average adult.

Josh Clark: Which is strange because that's about the same density for a chimpanzee? Did you know that?

Chuck Bryant: I did, and this is where it gets a little more interesting. Let's get all that sciency stuff - get all those terms out of the way. Now we're talking about chimps, and this is something I did not know until I read this. We actually don't have fewer hairs than a chimpanzee. It's the size of the hair, actually.

Josh Clark: Yeah, they're shorter and less coarse. So we have about the same number of hair follicles, or at least the same density of them as a chimp.

Chuck Bryant: Yeah. I bet no one would answer that unless they knew.

Josh Clark: No, but we could. We should totally go to trivia night.

Chuck Bryant: And now the dozens of people who listen to our podcast can know that, too.

Josh Clark: Exactly.

Chuck Bryant: But we also - on the chimps, we also share the same hairless parts, which is lips, palms and soles of the feet. No hair.

Josh Clark: I have hair on my palms.

Chuck Bryant: Well, I'm not gonna go there. Hey-oh. So Josh, do we need to talk about some theories?

Josh Clark: Yeah, I like this. This is why I've thought about this before because we were taught this kind of stuff in anthropology. My anthropology classes!

Chuck Bryant: You're the wiz.

Josh Clark: So my favorite theory - this is the one that makes the most sense to me, is that we started losing our hair when we became bipeds. If you look at most primates, they have a tendency to walk on their knuckles as well as their foot. That's how they move most quickly, which would require you would have a lot of hair on your back because then that whole area is exposed to the sun. The whole point of hair - well, actually, there's two points. Right? One is to regulate body heat, to keep your body warm, and the other is to protect from UV radiation from the sun.

Chuck Bryant: Yep, pretty cool.

Josh Clark: So once we started walking upright, we needed hair on our head, some on our shoulders maybe, a little on our back, some on the chest, and then everything else is kind of sexual. Right?

Chuck Bryant: Absolutely. I think about one-third of our bodies are exposed to sunlight once we started walking upright.

Josh Clark: Right. That's the one that makes most sense to me, but that's pretty far from the only theories. What else you got?

Chuck Bryant: Well, there's another one that I thought was kind of cool that one theory was that early man was a water dwelling ape. So since they were in the water, you don't need hair in the water. You don't see a lot of hairy fish.

Josh Clark: No, nor hippopotami or rhinos or -

Chuck Bryant: Elephants.

Josh Clark: Yes.

Chuck Bryant: Spend a lot of time -

Josh Clark: And they're all mammals. They have very sparse hair growth. Right? Because they're in the water a lot!

Chuck Bryant: Absolutely. So I kind of like that one.

Josh Clark: Yeah, that one makes sense. The other one that makes sense to me is that about 1.7 million years ago, we went from basically a forest dwelling species to kind of moving more out in the open. And since we're in the forest, we would not be exposed to the sun as much, and it'd be cooler because we're out of the sun. So we would need more hair to keep our body temperatures higher. Right?

Chuck Bryant: Right.

Josh Clark: Once we move out into the open savannah, we don't need the hair anymore.

Chuck Bryant: Why did we move out there? Was that when we started developing weapons and stuff?

Josh Clark: We always moved for food. Usually food is the basis for migration.

Chuck Bryant: That's where all the good meat was.

Josh Clark: Yeah. Okay, so the thing is if we lose our hair and we're now exposed to the sun, Chuck, we still need to protect ourselves from UV rays. But we need to use a method that doesn't keep us hot. Right? Enter skin pigment.

Chuck Bryant: This is news to me.

Josh Clark: They have - there is this researcher in 2000, Dr. Roslyn Harding at Oxford, and she went back and traced the evolution of the MC1R gene. This is the gene that produces either a dark pigment or a lighter, reddish pigment depending on where we live and our exposure to the sun. The closer you live to the equator, the darker pigmented you're going to be because it protects skin from sun cancer - skin cancer.

Chuck Bryant: Sun cancer, I like that.

Josh Clark: Sun cancer, it's the worst kind. So Professor Harding - or Dr. Harding, I'm sorry, traced the mutations on this gene as they're found in African populations, which strangely enough, there are no mutations. Or I'm sorry. There's no variations among Africans of this gene. And if you go and look at Asians, you look at people of Nordic descent, Native Americans, they all - we all have the MC1R gene, but there's variations on it. In Africans, it doesn't matter where you go on the African continent. You find the same exact gene with the same exact mutations.

Chuck Bryant: Interesting. And that's the birthplace of humanity many believe.

Josh Clark: Yes, sure.

Chuck Bryant: Including myself.

Josh Clark: Which I was also surprised - we apparently only exited Africa within the last 50,000 years. I thought it was way further back than that. But I read an article in The New York Times that said different.

Chuck Bryant: Wow, and they know.

Josh Clark: Sure. So anyway, Dr. Harding traced the evolution of this gene through mutations back to about the last time it swept through the African population, and she found that was about 1.2 billion years ago. The point of this is when this gene, when this mutation would have swept through, thus darkening everyone's pigment, we would have needed it then. So for at least the last 1.2 million years, Dr. Harding posits that we've been hairless. Pretty cool, huh?

Chuck Bryant: Yeah. It all makes sense.

Josh Clark: It does.

Chuck Bryant: I love it when it comes together like this. It all makes sense. But I also like biological and anthropological abnormalities that don't add up.

Josh Clark: I know you do. Let's hear about it.

Chuck Bryant: Well, no. I don't - well, are you talking about the hairy guys?

Josh Clark: The very hairy guys. Yeah.

Chuck Bryant: That actually wasn't a setup, but I'll take it. We are talking about hypertrichosis, which some people might have seen - they're called the wolf people.

Josh Clark: I don't know if they call themselves that.

Chuck Bryant: Well, they may not, but that's what they're called in the research I've done. Victor, Larry, and Gabriel Danny Ramos Gomez are in a family of 19 that spanned five generations.

Josh Clark: Wait, what?

Chuck Bryant: That's their name.

Josh Clark: No, a family of what?

Chuck Bryant: A family of 19.

Josh Clark: Holy cow.

Chuck Bryant: Yeah, exactly. Well, that's 19 over five generations.

Josh Clark: There is bound to be some genetic mutations in a family of 19.

Chuck Bryant: Absolutely. They all suffer from that rare condition. It's called congenital generalized hyphertrichosis in their case, and basically, what that means a lot of body hair. We're talking 98 percent of their body is covered in hair.

Josh Clark: Yeah, I was looking at the picture that you have, and you can basically see their eyes.

Chuck Bryant: Yeah, and around the lips.

Josh Clark: Yes, and around the lips. They look kind of like they're wearing hairy ski masks.

Chuck Bryant: Yeah.

Josh Clark: Yeah, and is that one of their little siblings?

Chuck Bryant: No, it says it's one of their fans. They're taking a picture with one of their fans.

Josh Clark: Very cool.

Chuck Bryant: And there is also a man in China named Yu Zenwan, and his claim to fame - he has the same thing. He's called the hairiest man in China. And hair covers 96 percent of his body, and he is trying to become a singer, apparently, and make it big as a singer, which I thought was pretty cool.

Josh Clark: Yeah, I think the Gomez brothers have him beat big time.

Chuck Bryant: Well, by 2 percent. Not much. And Yu has actually made his entertainment debut at the age of six in a movie called A Hairy Child's Adventure.

Josh Clark: What?

Chuck Bryant: So early on, he felt like he was exploited somewhat and he was ashamed.

Josh Clark: I'm sure.

Chuck Bryant: But he's learned to live with it and now kind of embraces it, which is kind of cool.

Josh Clark: A Hairy Child's Adventure. I'm looking that one up. I'll be it's riveting.

Chuck Bryant: So that is hypertrichosis in a nutshell. There's a lot more - maybe we should do a full podcast on this. It's pretty interesting, actually. But they - you know, shaving, plucking, electrolysis, and laser removal. There are different cosmetic things you can do to help that out.

Josh Clark: You know, I also did a tad bit of research on that, and you can - there's an acquired version. There's genetic version. There's an acquired version, and through malnutrition, you can develop this.

Chuck Bryant: Well, your starvation diet, you better watch out, buddy.

Josh Clark: That explains the hair on the back.

Chuck Bryant: Is it sprouting more and more, lately?

Josh Clark: Yeah, it is, and it's getting kind of billy goat-esque.

Chuck Bryant: Ew. I had a pet goat. Did you know that?

Josh Clark: I did not.

Chuck Bryant: Yeah, it's good stuff.

Josh Clark: How was its hair? Good growth pattern?

Chuck Bryant: Yeah, coarse. Goats are really great pets, actually. Very affectionate!

Josh Clark: Yeah, they are. They can cause some serious allergies, though.

Chuck Bryant: Oh, really?

Josh Clark: Sure.

Chuck Bryant: I didn't know that.

Josh Clark: You do now.

Chuck Bryant: So here is to you, Nester, my goat.

Josh Clark: Hey, Nester thanks for listening. You want to do one last thing?

Chuck Bryant: Sure.

Josh Clark: So what's the deal with groin hair and armpit hair? These places aren't exposed to the sun any longer. If they are, it's at like Camp Sunshine nudist resort.

Chuck Bryant: You tell me. Camp Sunshine was actually a camp for a kids with cancer, so I doubt that's not a nudist resort.

Josh Clark: Well, there is another one. You're thinking of -

Chuck Bryant: Camp Sunburst.

Josh Clark: No, it's Camp Sunshine in upstate New York. It's funded by the same people, strangely enough.

Chuck Bryant: That's awesome.

Josh Clark: No, the theory - no, I guess hypothesis.

Chuck Bryant: Right, not a theory yet.

Josh Clark: Would be behind why we have groin hair or armpit hair is because these places are where we emit the most - do you see where I'm demonstrating? Right here, Chuck. Look down here. These are where we produce the most pheromones, and the hypothesis is that the hair acts as kind of like an amplifier for these pheromones.

Chuck Bryant: Because it traps in the smells.

Josh Clark: Mine does.

Chuck Bryant: Interesting. What a grizzly topic.

Josh Clark: It really is.

Chuck Bryant: Kristen Conger wrote this. Right? Our colleague!

Josh Clark: Yeah, way to go, Conger. If you want to read it, you can type in why do humans have body hair in the handy search bar at HowStuffWorks.com. Okay. So we did that. All right, so that's why do humans have body hair. Right, Chuck?

Chuck Bryant: Uh huh. Because we need it!

Josh Clark: Yeah, I guess. Although, if we ever make it back into the water, prepare to go bald.

Chuck Bryant: And it's funny, hair human head hair has become one of the more distinct features that people have hair dos, and it's a very cosmetic thing. It's not just - it's there to protect our head.

Josh Clark: But it's also to look cool.

Chuck Bryant: Yeah, that's what I'm trying to say.

Josh Clark: Yeah, get a Mohawk maybe.

Chuck Bryant: Sure.

Josh Clark: Okay, well, let's plug something, Chuck.

Chuck Bryant: You. You plug.

Josh Clark: Okay, I'll plug. Let's plug the blogs. Chuck and I have a blog called Stuff You Should Know, appropriately enough, and we just post about all sorts of cool stuff. Chuck does a podcast goodness roundup every Friday, too. And we post each once a day every day during the week, and you can find it on the right rail on the homepage of HowStuffWorks.com, and there's our blog plug, which means -

Chuck Bryant: Listener mail time. Josh, today, I'm just going to call this the great Australian toad wart correction cast. We missed quite a few things on this one, I'm not ashamed to admit. That happens occasionally, and it happened this time. So here we go with corrections for the do toads cause warts.

Josh Clark: I see that part of it has been redacted.

Chuck Bryant: Right because someone was wrong. They wrote in and said that toads were not in Perth, but I went back and listened, and you said that they were heading toward Perth, and I sent the guy a link to an article that verified that they are indeed heading toward Perth and are going to make it there. So beyond that one, Josh, at one point, you said there are no predators that have figured out how to eat the cane toad because of the toxins on its back. And apparently, an Australian woman wrote in and said that crows have learned how to flip them over and attack the belly of the cane toad.

Josh Clark: Yeah, I'll be that's unpleasant sensation.

Chuck Bryant: So thank you for that. We don't have names. I apologize about that, folks. I was short on time. We also mispronounce HPV, which is -

Josh Clark: I know.

Chuck Bryant: Go ahead and say the real word.

Josh Clark: Human papilloma virus.

Chuck Bryant: Right. Yep. And we said pavlova virus. And that was my fault. We all know that pavlova is a dessert and was a famous ballet dancer. And you and I are both into eating dessert and watching ballet, so we probably just got mixed up.

Josh Clark: At the same time, too.

Chuck Bryant: I apologize about the mispronunciation. Josh, you said there are alligators. You said it kind of in a flip way. In Australia, not true. It's crocodiles.

Josh Clark: Wow, were we drunk during that one?

Chuck Bryant: No, we weren't, but the list goes on. I mispronounced salicylic acid. I apologize about that. And that is the last correction. But we should mention a couple of folks wrote in and talked about ways to get rid of warts that we did not know.

Josh Clark: Okay, let's hear them.

Chuck Bryant: Duct tape was the most well regarded. A lot of people said if you put duct tape on it and leave it for a little while; it will get rid of your wart.

Josh Clark: How long is a little while? Did you get an impression?

Chuck Bryant: No, I didn't.

Josh Clark: Until the wart goes away.

Chuck Bryant: Yeah, I would guess so. And then Chris from LA, he calls it Lower Alabama, which I always think is funny. He said breast milk, and I haven't heard that one, so that is unverified, but that's what Chris says.

Josh Clark: Chris may just have a thing. Well, yeah, thank you for all those corrections. Do you want to get the Eau Claire, Wisconsin? It's Eau Claire, Wisconsin.

Chuck Bryant: And Wisconsin folks wrote in and said, "No, no, no."

Josh Clark: Actually, yeah, I guess we should say it's Eau Claire, Wisconsin.

Chuck Bryant: Wisconsin.

Josh Clark: Yeah, so thanks for everybody who wrote in to correct us, whether you were correct or not. You know, if you mentioned Perth, that's okay.

Chuck Bryant: The Aussies loved it, though. They love hearing podcasts about themselves. We got a lot of good feedback.

Josh Clark: We'll have to do that a little more often. Okay, so if you want to send us any words of encouragement, any words of derision, anything at all, you can shoot an e-mail to StuffPodcast@HowStuffworks.com.

Announcer: For more on this and thousands of other topics, visit HowStuffWorks.com.