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Are Yawns Really Contagious?

Does looking at this cat make you yawn? Why are yawns contagious? It may be because humans are social animals.

Why are yawns contagious? Why do we hiccup? How do teeth get loose? Why do your ears hurt when you drive up over the mountains? Why do we get dizzy when we spin? Why do people slip? Why do people faint? Why do we have saliva and mucus? Why do people cry when they get hurt? How do voice boxes work? Why does your voice sound weird when it's recorded? Dr. Lori Racha has more answers to your body questions.


"Why when we're tired do we yawn?" - Liron, 9, Riverdale, N.Y.

"Why are yawns contagious?" - Maya, 12, California and Olive, 6, Seattle, Wash.

"Up to 50 percent of people will yawn, just hearing that someone is talking about yawning. There's much that's not understood about yawning and there are several different ideas of why people yawn.

"There's some belief that even the very earliest human, so even before there was a real communication system of language, that early humans would yawn and that maybe was a way for them to signal to each other that maybe their level of alertness, that they weren't going to be able to watch out for that big predator animals or something like that, or to signal that maybe it was then time for everyone to go to sleep. Maybe it was a way in early humans of coordinating some of their sleep activity.

"One theory also says that it may just be simply mimicking behavior. I don't know if any of you have noticed that if you see someone and they are smiling that you are likely to smile back. That's just a simple mimicking behavior. I don't think we're telling ourselves, 'oh, this is one of those times I must smile.' But just seeing the human face with a smile often causes us to smile back. And that's a very good reason for all of us to smile as much as we can because I think it's important for all of us to do our part to try to keep people feeling positive and happy."

Credit courtesy of their parents
Liron (left) is in fourth grade. She lives with her parents and her three older siblings. Liron enjoys imaginative play, reading biographies, and playing board games. Olive is a kindergartener in Seattle, Wash. She loves to swim in pools and oceans, cook with her dad, and play with her little sister, Etta.

"Another factor is that your age plays a role, so even though babies, as soon as they're born they can yawn, they don't have contagious yawn. It doesn't seem that humans become contagious yawners until we're about age four. The other interesting thing to know is that humans and other social mammals, so animals that work together, have some kind of communication with each other, are the only living things that we know of that have contagious yawns. So it does seem to be something important to our social structure or how we are with other people. But I can't tell you exactly why that happens.

"The last thought that I wanted to share with you was that some researchers feel that yawning may have a role in helping to keep the brain's temperature down. So that sounds kind of funny how that could happen. But if you think about it our bodies are about 98.5 degrees Fahrenheit and our outside world is usually cooler than that. So when we yawn we bring in a lot of cool air into our mouth. Above our mouth is the palate, but above that is the sinuses and actually then the base of the brain. So when you're bringing in cold air, you may be having a little bit of a cooling effect on the brain.

"Now when I have a fever I don't feel like I yawn more. But I don't know if I've really thought about that but that's another interesting thought about what yawning could do."

"Why do I get the hiccups?" - Estelle, 2, Nashville, Tenn. and Max, 9, Escondido, Calif.

"... Is it triggered by laughing?" - Jude, 10, Waitsfield, Vt.

"Hiccups are some of the most interesting, fun thing that I think our body does. Hiccupping occurs really early. So when we are the developing baby in our moms' abdomens we are making hiccup sounds. One of the things that really makes sense to me is the response to hiccups after eating. So there's a nerve that actually runs on the underside of the stomach. If you take your hand and make a fist, that's about the size of your stomach. Now when you eat food that stomach expands and gets bigger, kind of like a balloon that you're blowing air into, when that expands it triggers that nerve that's on the underside of the stomach to say 'oh I'm getting expanded' and it causes this funny little contraction of the muscle in your chest, lower chest that's involved with breathing called the diaphragm, and it causes these hiccup.

"As you get older, it's almost like the body gets more used to this, right? It's kind of predictable, they're eating again, the stomach is going to get bigger and you tend to have fewer hiccups as you get older. Many kids can have learned that they can make themselves hiccup by swallowing a lot of air and that can also make you burp."

Credit courtesy of their parents
Max, 9, (with his twin sister Stella) is a voracious reader and plays the drums. He loves video games, too. Jude (center) is a lover of elephants, rocks, travel, maps and maps. Estelle (right) is 2, and was born in Vicenza, Italy. She is a very joyful, intelligent and curious lover of life.

"Is it triggered by laughing? When you laugh you do tend to swallow a lot of air. Laughing and crying actually both are situations where you can develop a lot of air in your stomach. And again I think that can trigger a trigger the hiccups too, so I guess the answer is yes. And sometimes hiccups just happen and it's not related to eating or anything else.

"But there are some things that you can do too. It does seem that if you drink some water sometimes that will help alleviate hiccups. Eating something sweet, now again, this would be a treat, this would not be something that we would want to do all the time. But sometimes eating something sweet seems to relax some of the muscles that are involved with hiccups and that can be helpful as well."

Listen to the full episode the answers to all of our other body questions.

How do teeth get loose? Why do your ears hurt when you drive up over the mountains? Why do we get dizzy when we spin? Why do people slip? Why do people faint? Why do we have saliva and mucus? Why do people cry when they get hurt? How do voice boxes work? Why does your voice sound weird when it's recorded?

Read the full transcript.

Melody is the Contributing Editor for But Why: A Podcast For Curious Kids and the co-author of two But Why books with Jane Lindholm.
Jane Lindholm is the host, executive producer and creator of But Why: A Podcast For Curious Kids. In addition to her work on our international kids show, she produces special projects for Vermont Public. Until March 2021, she was host and editor of the award-winning Vermont Public program Vermont Edition.
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