Boogers and sun sneezes: Know your nose

NARRATOR 1: You're listening to Brains On, where we're serious about being curious.

NARRATOR 2: Brains On is supported in part by a grant from the National Science Foundation.

[MUSIC PLAYING]

MOLLY BLOOM: Hello, hello, hello. I'm your host, Molly Bloom. And today, our producer, Marc Sanchez, is joining me.

MARC SANCHEZ: Hello. Hello, hello, Molly. Today we're going to tackle a question about sneezing. Why does the heat of the sun provoke sneezing and not the heat of the fire? Interesting question, right?

MOLLY BLOOM: Right. But that wasn't from one of our listeners.

MARC SANCHEZ: Nope. This question was asked over 2,300 years ago.

MOLLY BLOOM: By Greek philosopher and scientist Aristotle.

MARC SANCHEZ: Which leads us to Kaitlyn and Megan from Portland, Oregon.

KAITLYN: Hi, I'm Kaitlyn, and I'm nine years old.

MEGAN: Hi, I'm Megan, and I'm seven years old. Our question is, why does the sun make you sneeze?

KAITLYN: Whenever I come out from the store, from school, and out to recess, if it's a sunny day and I happen to glance up at the sky, I sneeze.

MEGAN: We don't know why we sneeze when we look up at the sun.

MARC SANCHEZ: They ask pretty much the same question as Aristotle.

MOLLY BLOOM: 2,300 years later. To find an answer, we turn to Dr. Louis Ptácek.

MARC SANCHEZ: He's a neurologist and human geneticist.

MOLLY BLOOM: Yeah, he studies the brain and the genes that make up all humans.

MARC SANCHEZ: So why do we sneeze when we look at the sun?

LOUIS PTÁCEK: The bottom line is that nobody knows.

MOLLY BLOOM: 2,300 years later, and still nobody knows.

MARC SANCHEZ: But Dr. Ptácek has looked into the phenomenon. It's called photic sneeze reflex.

LOUIS PTÁCEK: You know what reflexes are. When you touch a hot stove accidentally--

MARC SANCHEZ: Ouch.

LOUIS PTÁCEK: --even before we realized that it's hot, we've begun to draw our hand away. There are many reflexes in all animals, but certainly in us humans. And so people speculate that perhaps photic sneeze is an abnormal reflex where a stimulus like bright light somehow leads to activity in the part of the brainstem where the nerves are that cause the sneeze to be initiated.

MARC SANCHEZ: Normally, sneezing is our body's way of getting an irritant out of our airways.

MOLLY BLOOM: Let's say you breathe in some dust or mold.

MARC SANCHEZ: Black pepper is always a good bet.

MOLLY BLOOM: Take a big whiff of black pepper, and it gets caught in the lining on the inside of your nose.

MARC SANCHEZ: The mucosa.

MOLLY BLOOM: Our bodies kick into action.

MAN: Pepper on the mucosa. Repeat. Pepper in the mucosa.

MARC SANCHEZ: First, the phrenic nerve sends a signal to the brain. Pepper alert. Pepper alert. Hey, brain, we got a pepper emergency. Don't worry. I got this. Diaphragm, contract.

MOLLY BLOOM: The brain sends a message back down the phrenic nerve, telling your diaphragm--

MARC SANCHEZ: The muscle beneath your lungs.

MOLLY BLOOM: --to contract and expel air.

MARC SANCHEZ: Which we know as-- [SNEEZES] a sneeze.

MOLLY BLOOM: So photic sneeze reflex triggers a sneeze even when there's no irritant present. Dr. Ptácek has been studying photic sneeze reflex over the years. It turns out Kaitlyn and Megan have their parents to thank for this condition.

LOUIS PTÁCEK: About 10% of the entire population has photic sneeze reflex. If someone doesn't and they hear about this, they say, wow, that sounds really funny. If you tell this story to someone who has photic sneeze reflex, they will often say, oh, really? Doesn't everybody do that? Because they do it and some of their family members do it.

It doesn't seem to have any benefit as pulling our hand away from a hot stove would. But it occurs in a large number of people for reasons that are completely unclear.

MARC SANCHEZ: So we know that sneezing from the sun is probably genetic. But we still don't know why some people are wired to do this. We know that about 10% of people sneeze when exposed to bright light.

MOLLY BLOOM: Like when you come out of a dark movie theater on a sunny day.

MARC SANCHEZ: But there's nothing really wrong with an extra sneeze now and then. So there's not much interest in figuring out how to stop this.

MOLLY BLOOM: But Dr. Ptácek thinks that finding the genes that cause photic sneeze reflex could help in treating people with more serious problems.

LOUIS PTÁCEK: In some percentage of patients with epilepsy, if some of those patients are exposed to a flashing strobe light, in some cases, that can precipitate a seizure. Some of your listeners will have heard about this in Japan, where a particular video game and the flashing movements on the screen was causing some children in Japan to have seizures, for example.

MOLLY BLOOM: A seizure is when brainwaves get out of their normal rhythm. And when they happen, they usually last for a few minutes.

MARC SANCHEZ: Now there's a lot of different ways seizures can be felt in a person's body.

MOLLY BLOOM: Some people feel nauseous or feel tingling in their bodies. Sometimes, they twitch or lose vision. Sometimes, a seizure comes on very strong, and a person will fall down and start shaking all over.

MARC SANCHEZ: Some people get seizures because of the way their brains work. Other people can have seizures triggered by outside factors like the video game Dr. Ptácek just mentioned.

LOUIS PTÁCEK: So there are many different reflex phenomena, some of which are problematic. I mean, having seizures, obviously, is a much more serious thing to happen than sneezing. But it is my thought that if we could understand what it is that causes photic sneeze reflex, that it might teach us something about some of these other reflex phenomena.

MARC SANCHEZ: Some mice and a handful of people are known to have seizures when they hear a loud noise.

MOLLY BLOOM: Dr. Ptácek's lab has been able to isolate and clone the gene that causes these kind of seizures. And in doing that, they might be able to figure out a way to stop those seizures.

MARC SANCHEZ: The same might be true for seizures brought on by strobe lights. And looking for a gene that causes photic sneeze reflex could be the first step.

MOLLY BLOOM: To Kaitlyn and Megan--

MARC SANCHEZ: --and all the photic sneezers out there--

MOLLY BLOOM: --there's no known reason for why you sneeze when you see a bright light.

MARC SANCHEZ: Maybe you can just think of it as being part of a special club, kind of a-- [SNEEZES] a sneeze club.

MOLLY BLOOM: In just a minute, we're going to answer more questions. Our listeners want to know about noses and what's inside them. But first, it's time for the mystery sound.

[WHISTLING]

CHILD: Mystery sound.

MOLLY BLOOM: Here it is.

[RATTLING]

Any guesses?

MARC SANCHEZ: Well, I have a pretty good guess, I think, as to what it is. I hear two clicking sounds. So there's that first initial little sound, and then there's a bunch of clicks. And I have heard that sound before I'm pretty sure at mini golf. Some people call it putt-putt.

MOLLY BLOOM: [LAUGHS] Do you want to hear it one more time?

MARC SANCHEZ: Yeah, let's verify.

MOLLY BLOOM: OK, here it is.

[RATTLING]

MARC SANCHEZ: Yep. I'm going to-- I'm going to stick with my guess, mini golf.

MOLLY BLOOM: What's happening at mini golf during that sound?

MARC SANCHEZ: Well, if you're talking about my mini golf, it's going to be a hole in one.

MOLLY BLOOM: Ah, OK.

MARC SANCHEZ: It's the ball going in the hole.

MOLLY BLOOM: The ball going in the hole in mini golf. All right. Here is the answer.

MADELEINE: I'm Madeleine from Pendleton, Indiana, and I'm eight years old.

JACKSON: I'm Jackson, and I'm five years old.

MADELEINE: That is the sound of a golf ball going in the hole.

JACKSON: I like that sound because it reminds me of my family playing miniature golf.

MARC SANCHEZ: I was right.

MOLLY BLOOM: Nice work.

MARC SANCHEZ: All my years of mini golf have paid off. Finally.

MOLLY BLOOM: Finally.

MARC SANCHEZ: You got to stay listening, though.

MOLLY BLOOM: Next time you're out and about mini golfing--

MARC SANCHEZ: --or soccering--

MOLLY BLOOM: --or just exploring your neighborhood--

MARC SANCHEZ: --keep your ears open for good mystery sounds.

MOLLY BLOOM: They're everywhere. You can send them to us by going to brainson.org/contact.

MARC SANCHEZ: And while you're there, you can send us the answer to this question we've been wondering about.

MOLLY BLOOM: If aliens came to Earth and you could only serve them one dish to introduce them to the food of our planet, what dish would it be and why? We'll include some of your answers in our series coming up about the science of cooking.

MARC SANCHEZ: So send us your dishes at brainson.org/contact.

MOLLY BLOOM: Marc, what would you serve the aliens?

MARC SANCHEZ: Well, for sure, I would serve the aliens a taco platter.

MOLLY BLOOM: Why?

MARC SANCHEZ: Because you can put anything in those delicious tortillas. You've got meat options, vegetarian options, vegan options, cheese options.

MOLLY BLOOM: And this is good for aliens because we don't really know what kind of food they're into?

MARC SANCHEZ: Yeah, they might just-- you could just even give them a plain tortilla, and that would be good.

MOLLY BLOOM: True. Who doesn't love tacos?

MARC SANCHEZ: That's right. Who doesn't? Speaking of tacos, I haven't had lunch yet. Adios.

MOLLY BLOOM: So who's going to co-host the rest of the episode with me?

SANDEN TOTTEN: Hey, guys, it's me, Brains On Producer, Sanden Totten.

MOLLY BLOOM: Oh, hey, Sanden. So I have to ask you, what dish would you serve the aliens?

SANDEN TOTTEN: Oh, well, you know, I have Swedish roots. I would serve them a pickled herring, a famous delicacy in my land.

MOLLY BLOOM: Why should that represent food to the aliens?

SANDEN TOTTEN: Well, I figure if they can get past the pickled herring and they still want to come meet us, they're probably pretty decent people, you know? Friendly, outgoing, and willing to give anything a try.

MOLLY BLOOM: That's a good thought. Well, if you have an idea for a dish like Marc and Sanden, head to brainson.org/contact.

SANDEN TOTTEN: And while you're there, you can also send us your questions. That's what Jordan did. Go, Jordan.

JORDAN: And my question is, why do sloths move so slow?

SANDEN TOTTEN: You'll hear the answer to that and learn about some superpower sloths have at the end of the show during our Moment of Um.

MOLLY BLOOM: And you'll also get to hear the latest group to be added to the Brains Honor Roll.

SANDEN TOTTEN: Those are the rad kids who make our show an awesome parade of ideas and voices by sharing stuff with us.

MOLLY BLOOM: Stay tuned. Now we're diving into a topic that we are very excited about.

SANDEN TOTTEN: Too excited, maybe. No. No, no, no, no way. How could you be too excited when it comes to something this incredibly cool? Of course, we are talking about snot, boogers, nose jams, schnoz jelly, whatever you want to call it.

MOLLY BLOOM: We are really excited because your questions led us to find out that nasal mucus, as it's formerly known, is really, really cool. Magical, even.

SANDEN TOTTEN: Our first booger question comes courtesy of Harrison in Lakewood Ranch, Florida.

HARRISON: My question is, how do boogers get in your nose? And why aren't they in other parts of your body?

MOLLY BLOOM: Very nice, Harrison. A two-part question. First, the source. Boogers come from mucus that's made in your nose. And it's basically superpowered. Dr. Holly Boyer, who's an otolaryngologist at the University of Minnesota, treats patients who have nasal and sinus issues.

HOLLY BOYER: I have a lot of experience with nasal mucus.

MOLLY BLOOM: And it's really important stuff. That mucus does some key things for your body. First, it makes sure the air you breathe in won't hurt your lungs.

HOLLY BOYER: It moisturizes the air that you breathe. If you go outside and it's cold and you breathe in through your mouth, it hurts your throat. It hurts your lungs. It kind of burns. But if you breathe through your nose, the air becomes completely humidified. By the time it reaches the back of the nose, it's almost 100% humidified. So the air that reaches your lungs is nice and wet, and it doesn't hurt your lungs.

SANDEN TOTTEN: The other thing that mucus does is it cleans and filters the air you breathe. And the way it does that is super cool. Your nose is constantly making mucus. It's made by what are called goblet cells in your nose.

HOLLY BOYER: The mucus in your nose is a sticky substance. It's made partially of water, actually, mostly water, about 95% water. More specifically, it's salt water. And about 5% of it is made of sticky substances like proteins and substances that your body secretes to make it sticky.

MOLLY BLOOM: And the stickiness is key. It acts as a kind of flypaper that traps nasty things that we don't want to breathe into our lungs.

HOLLY BOYER: Viruses, fungus, bacteria, dust, pollens. There are chemicals in there that make it really hostile for bacteria and fungi and viruses to live. So there are chemicals and cells that attack those invaders. There's also antibodies to recognize whether or not it's something good or something bad.

MOLLY BLOOM: So once these get caught, where do they go? It turns out your nose is an efficient self-cleaning system, basically replacing your nasal mucus every 20 minutes.

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HOLLY BOYER: So the same cells that line the inside of the nose that secrete the mucus also have little tiny microscopic hairs on them. And it's really interesting that the flow of mucus is preprogrammed. It constantly is being swept into the back of the nose, except for a very small part in the front of your nose, which gets propelled forward, which is in a very convenient place for your fingers to reach it.

SANDEN TOTTEN: These hairs Holly mentioned aren't the ones you can see at the front of your nose. Those hairs are great for filtering out big things like bugs and dirt. The hairs that sweep the mucus back and out of your nose are very, very tiny.

HOLLY BOYER: You can only see these with a microscope. And they're constantly moving. So that sticky mucus that's full of all that bad stuff that it filtered out of the air, you swallow that. And it's fine to swallow it. An interesting fact is that your nose produces one to two liters of mucus per day. And most of that you don't even notice because it's continually being swept into the back of your nose by those little hairs, and you just swallow it.

Good thing about swallowing is that when it goes into your stomach, anything that's alive like a virus or bacteria or fungus dies because of the acid content in your stomach. So the acid in your stomach kills all that stuff that your nose so efficiently filtered.

MOLLY BLOOM: So it's pretty sophisticated. The air you breathe in through your nose goes to your lungs, but the mucus produced by your nose goes into your stomach. Now, like Holly said, most of the mucus is swept back and swallowed, but a small bit at the front is pushed forward where it becomes boogers. OK, now for the second part of Harrison's question.

HARRISON: Why aren't they in other parts of your body?

HOLLY BOYER: That's a really good question. But there is a logical answer to that. So there are other places in your body where you make mucus. You make mucus in your stomach and in your GI tract and in your lungs. Your nose, however, is where all of the air in the atmosphere comes into your body, so it dries out. So boogers are just dry mucus. And it's just airflow.

SANDEN TOTTEN: Our next mucus mystery comes from Milo from West Palm Beach, Florida.

MILO: My question is, why does your nose get stuffy when you're sick?

MOLLY BLOOM: Good question, Milo. I mean, you'd think our bodies would try to help us breathe by giving us as much air as possible, not try to make it harder to breathe. Here's Dr. Holly Boyer again with the answer.

HOLLY BOYER: So when you get sick, especially with viral infections, the most common infection in the nose, the virus goes in, and it infects that lining tissue to the nose and all of those cells that are producing mucus. And they have those little hairs. Those get damaged. And when they're damaged, there's irritation of the underlying tissue. And one of the responses that your body has is to secrete lots of mucus.

Part of that is probably to try to wash the debris out of the nose. And that's why you have thicker mucus. It's more colored when you have an infection, is that it's full of debris and dead cells. So that increased amount, it may be somewhat protective in that it's trying to wash some of that away. And it also promotes healing because for the inside of your nose to heal after a viral infection, it's almost like healing from a burn. The inside needs to be healthy and moist to promote that healing.

MOLLY BLOOM: Our next and last question is from Lydia of Holland, Michigan.

LYDIA: Why do you get a runny nose when you're outside in the cold? Shouldn't your snot freeze?

SANDEN TOTTEN: Great question. Not only is our nose able to humidify the air we breathe, it's also an excellent thermometer.

HOLLY BOYER: So there's a really sensitive temperature-sensing system in the nose. And when you breathe in cold air, it increases the blood flow to your nose because your nose is really efficient at also warming the air. So like I said before, when you breathe in cold, dry air, it hurts your lungs. The coldness hurts your lungs too. So the increased blood flow to the nose warms the air that you breathe. As you increase the blood flow, you also increase some of the stimulation to the nose that produces secretions.

MOLLY BLOOM: So more blood in the nose means more mucus produced by those cells. And it's warm enough inside your nose that it doesn't freeze. So our noses and the mucus that's in them are pretty amazing and important.

SANDEN TOTTEN: Dr. Holly Boyer hopes you give a little love to the superpowered nasal mucus that keeps us healthy. So maybe next time you blow your nose, say thanks to all that mucus before you toss it out.

HOLLY BOYER: Mucus is good for you. It's protecting your lungs. It's filtering out things that could hurt you. And even though people think it's annoying and gross, if you didn't have it, you'd have a lot more trouble.

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MOLLY BLOOM: That's it for this episode of Brains On.

SANDEN TOTTEN: Brains On is produced by me, Sanden Totten.

MOLLY BLOOM: Me, Molly Bloom.

SANDEN TOTTEN: And Marc Sanchez, who's still eating lunch somewhere.

MOLLY BLOOM: We had production help from Lauren Dee and John Lambert and engineering help from Veronica Rodriguez.

SANDEN TOTTEN: And did you know that we have started a new podcast called Smash Boom Best? It's a show where we pick two awesome things against each other to decide which one is the smash boom best. Some of the matchups include super speed versus super strength, pizza versus tacos, and cats versus dogs.

MOLLY BLOOM: You can find Smash Boom Best wherever you get your podcasts.

SANDEN TOTTEN: Now, before we go, it's time for our Moment of Um.

[VOCALIZING]

JORDAN MAJOR: My name is Jordan Major from Los Angeles, and my question is, why do sloths move so slow?

MOLLY BLOOM: Well, the easy answer for that question is that sloths move slow for protection. Mainly, when you think about it, an animal living in the rainforest, if they're not moving, they're probably not going to be seen. So that is their ultimate defense from predators is to be able to camouflage themselves in the canopies.

TARYN DWYER: So my name is Taryn Dwyer, and I'm a zookeeper here at the Minnesota Zoo, working in our close encounter department. So sloths don't move far at all during the day, and they only move actually probably less than half of a football field in one day. If they did want to move quick, they definitely could. They're really highly adapted to be able to move around in those trees.

Part of the reason why they are so slow-- it's really interesting-- is because their metabolism is so slow. They're eating leaves, but it's not giving them a lot of nutrients. They're not getting a lot of fat or protein from it, so they're actually conserving their energy by moving slow. And one thing that helps them to be a really good swimmer is that they can actually slow down that metabolism like one third of the normal rate. They can hold their breath underwater for about 40 minutes if they wanted to.

MOLLY BLOOM: I'm no sloth, so I'm going to sprint through this list of names. It's time for the Brains Honor Roll.

SANDEN TOTTEN: These are the excellent humans who make our show way, way better by sharing their way, way awesome ideas.

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[LISTING HONOR ROLL]

We'll be back soon with more answers to your questions.

MOLLY BLOOM: Thanks for listening.

[THEME MUSIC] Ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, Brains On