Why Do Yawns Spread?

The child listens. The parent reads. This page helps you answer the questions your child may ask after the story. You can see the story script with the script button during play.

What this story is about

When someone yawns, we often yawn too. Children know this, and so do adults. This story follows how people checked it. They showed yawn videos and no-yawn videos and counted. They tested dogs, chimps, elephants, and birds. They watched babies yawn before birth with ultrasound. The answer has two parts. Many tests show that yawns spread. Why they spread, and what a yawn does, are still being argued.

How people found out

Seeing it, or just thinking about it. A yawn can start when you see someone yawn. It can also start when you hear a yawn, read about one, or think about one. This is well recorded (PMID 15820652). In one test, people only heard sounds. Yawn sounds made people want to yawn more than breathing sounds or mixed-up sounds (PMID 19679768).

Show a video, then count. The basic method is simple. Show a yawn video and a control video. The control has other mouth moves, scratching, or laughing. Then compare the number of yawns. Two tests used 171 and 333 students. People copied yawns, scratching, and laughing a lot (PMID 29771564). In another study, 328 people watched a three-minute yawn video. Each person caught yawns about the same amount each time. This was true in the lab and online (PMID 24632594). Older people caught yawns less. But age explained only 8% of the differences. Most of the differences were not explained (PMID 24632594).

When children start. One study looked at 120 children aged one to six. Catching yawns went up a lot at around age four (PMID 20840244).

When told not to yawn. Thirty-six adults watched yawn videos. They were told to hold back their yawns. Their wish to yawn got stronger. The shape of the yawn changed, from full to held-in. But how much each person caught yawns did not change (PMID 28867202).

When someone is watching. In the lab, yawns spread less when people were told someone was there. They also spread less when someone was really there (PMID 27112374). In virtual reality, people could not see the tester. But yawns still went down when the tester was in the room. Putting cameras or human-like avatars inside the virtual world made no difference (PMID 30670744). This is useful when you try it at home.

Animals. A person yawned in person in front of 29 dogs. Twenty-one dogs yawned back. No dog yawned at other mouth moves (PMID 18682357). But in another test, 15 dogs watched human and dog yawn videos. Only one dog clearly yawned back (PMID 19452178). In a test with 60 shelter dogs, a stranger yawned. Twelve dogs yawned only to the yawns. But the group as a whole did not show yawn spreading (PMID 23670215). One team looked again at six dog studies with a new math method. The results strongly support that dogs catch yawns (PMID 32075525).

Twenty-three chimps came from two groups. They yawned more at yawns from chimps they knew (PMID 21494669). Three of seven African elephants yawned back when a keeper they knew acted out a yawn (PMID 32457923). The budgie was the first non-mammal with test proof of catching yawns (PMID 26012708). But galahs, birds with a similar life, showed no proof in two tests. Fifteen galahs were tested (DOI: 10.26451/abc.12.02.01.2025). Then people turned it around. In an online study, 296 people saw yawns from fish, frogs and other amphibians, reptiles, birds, mammals, apes, and pets. People said they yawned back. The kind of animal made no clear difference (PMID 35892558).

Before birth. One study filmed 15 healthy babies before birth. It used 4D ultrasound at weeks 24, 28, 32, and 36. It found that yawns could be told apart from a simple open mouth (PMID 23185638). But other work says studies on yawning before birth often disagree. The ways of spotting a yawn have problems (PMID 41739743). A recent study used ultrasound too. After the mother yawned, the baby yawned more. In the control condition, it did not go up (PMID 42092355). The authors say the mother's actions might shape the baby's yawns. This is one study. The abstract does not give the number of babies (PMID 42092355). This result sits uneasily with growth studies. In children, catching yawns rises a lot at about age four (PMID 20840244). In orphan chimps, babies did not catch yawns (PMID 24146848). In puppies, only dogs older than seven months did (PMID 23076724). From this abstract alone, we cannot tell if the rise before birth is the same thing as catching yawns after birth. The story says it is only one study, it does not fit well with the age-four studies, and it needs more checking.

Answers you often hear

"We yawn because we are sleepy." Partly true. In adults, yawns rise and fall with sleepiness. But just after waking, people yawn a lot without being very sleepy (PMID 20357459).

"We yawn because we need more oxygen." Not supported in the test that checked it. If low oxygen caused yawns, breathing pure oxygen should reduce them. To test this, a 1987 study used college-age people. They breathed pure oxygen, air with 3% or 5% carbon dioxide, or normal air. Both gases made people breathe faster. But neither changed yawning. Exercise that doubled the breathing rate did not change yawning either (PMID 3120687). The authors say yawning does not mainly serve breathing (PMID 3120687). On the other side, a 1989 review used past papers and the writer's own watching. It said yawning works to fix low oxygen in the brain (PMID 2558182). A 2010 review said breathing ideas and other body ideas lack proof (PMID 20382180). In what we found, the 1987 study is the only direct test. So the story says only, "at least in this test, air was not the answer."

"A yawn cools the brain." Many tests support it, but it is still an idea. See the section below.

Questions your child may ask

"Will my dog copy my yawn?" It might. A new look at many studies supports that dogs catch yawns (PMID 32075525). But the share of dogs that yawned back was very different from test to test (PMID 18682357, PMID 19452178). If your dog does not yawn back, that is normal.

"Do yawns spread more between friends?" Some studies say yes. Some say no. See below.

"What happens if I hold in a yawn?" In one test, people told to hold back wanted to yawn more. How much they caught yawns stayed the same (PMID 28867202). We did not look at whether holding in a yawn is bad for you.

"Why do animals yawn?" One study looked at 1,291 yawns from 101 kinds of animals. There were 55 mammals and 46 birds. Animals with bigger brains and more brain cells had longer yawns (PMID 33958700). The authors say this supports the brain cooling idea (PMID 33958700). Body size alone did not explain this. With similar brain and body size, mammals yawned much longer than birds (PMID 33958700). So tell your child "animals with bigger brains and more brain cells have longer yawns," not "bigger animals." Why animals yawn is still argued. This result fits the brain cooling idea.

What we know and what we do not know yet

What we know. In people, yawns spread (PMID 15820652, PMID 24632594). Some animals also show it in tests: dogs (PMID 32075525), chimps (PMID 21494669), and budgies (PMID 26012708). Even people who doubt the body role of yawning agree on this. They say the only clear effect of a yawn shown so far is that it spreads. This is in humans, some apes and monkeys, and maybe dogs (PMID 21168437).

Why do yawns spread? People argue about empathy. Here is support for a link to closeness and empathy. In gelada monkeys, yawns spread more between those who cleaned each other's fur more. This stayed true after counting how near they sat (PMID 19889980). Twenty-five dogs yawned more for their owner than for the tester. Their heart rate did not change, so stress is a less likely reason (PMID 23951146). Wolves also caught yawns more from close pack members (PMID 25162677). In two tests with 504 students, people who caught yawns had empathy scores higher by half a standard step. But there was no direct link to helping others (PMID 29771564). Pregnant women caught yawns more than women who were not pregnant (PMID 34255275).

Here is the other side. A new look at six dog studies found no proof that closeness mattered. Dogs also did not yawn more for a kind helper. The authors say empathy does not explain dog yawn spreading. They doubt that yawn spreading is a sign of empathy in mammals (PMID 32075525). In 35 puppies, closeness did not change how much yawns spread. Only dogs older than seven months caught yawns (PMID 23076724). Thirty-three orphan chimps also showed no closeness effect (PMID 24146848). In the 328-people study, empathy made no difference once age was counted (PMID 24632594). A 2017 review checked the link between yawn spreading and empathy. It found the proof did not match and could not give an answer. It named two things that may mix in: where people look, and holding back when others are near. It asked for stronger tests with clear measures (PMID 28735879). The story does not pick one side as the answer.

Why do we yawn at all? The brain cooling idea and its limits. People watched yawn videos while breathing only through the nose. No one yawned back. With mouth breathing or no direction, about 48% did. With a 46°C pack or a room-temperature pack on the forehead, it was 41%. This number joins both groups. With a 4°C pack to cool the forehead, it was 9% (DOI: 10.1177/147470490700500109). So warm and normal packs were not split apart. Yawns dropped only with cooling. In another test, people held packs on the neck. With a cold pack, only 48.5% felt the urge to yawn. With a warm pack, 84.8% did. The number of yawns per person was 0.364 and 1.121, about three times more (PMID 31022409). In a desert in the United States, people walking outside saw yawn pictures. In winter at 22°C, 45% yawned. In early summer at 37°C, 24% yawned (PMID 21960970). In another place, it was 18.3% in winter at 1.4°C and 41.7% in summer at 19.4°C. These people reported their own yawns (PMID 24721675). The researchers see this as a "thermal window," a range of air heat where yawns happen most (PMID 24721675). In rats, yawns and stretches came when the front of the brain got warmer. Then brain heat went back to normal (PMID 21031034). In rats and budgies, the face got about 0.3 to 0.4°C cooler 10 to 20 seconds after a yawn (PMID 28049450, PMID 29435482). The rat brain study used surgery to put heat probes in the brain. So we left it out of the story. In 2012, a review that backs this idea was written. It said five years of tests kept matching the cooling idea, and no study found the opposite (PMID 23293583).

There are limits too. A 2010 review said ideas about a body role lack proof. It said the idea that yawns send a message has more and more support. The message may be sleepiness, boredom, or mild stress (PMID 20382180). That review and the cooling researchers argued back and forth (PMID 20883719, PMID 21168437). These doubts came in 2010 and 2011, before the later neck, season, and face heat tests (2014 to 2021). In one study, 22 healthy people got a shot of a germ substance that caused a fever. It was compared with a placebo. Yawning went up while body heat was rising. But body heat rise and yawn count were not clearly linked. The authors said more studies are needed to show the cooling role (PMID 28939427). Babies before birth depend mostly on the mother for body heat. But they still yawn. This is a gap the cooling idea does not directly explain (PMID 41739743).

What we left out of the story. Some studies look at yawn spreading in autistic children. The results do not agree. One study found the gap got smaller when children were guided to look at the eyes, or when parents did the yawning (PMID 30924430). Most differences in catching yawns are not explained (PMID 24632594). Proof for a link to empathy does not match (PMID 28735879). So from what we found, there is no basis to judge empathy or growth by how much someone catches yawns.

Things to try together

• In the evening, do one big fake yawn in front of the family. Count with your child how many people yawn back. Yawns spread less when someone is watching (PMID 27112374). So it is better to keep the counting a secret until the end. But the counter is still in the room, so a secret only lowers the feeling of being watched. Not staring after the fake yawn may also help. People yawn less when watched directly (PMID 27112374). With only one fake yawn, no one may yawn back.
• On another day, do not fake a yawn. Just talk about yawns. Thinking or talking about yawns can make people yawn (PMID 15820652).
• Tell your child it is fine if someone does not yawn back. People differ a lot in catching yawns, and most of it is not explained (PMID 24632594).

Evidence

• "Contagious yawning and the brain." (2005) — PMID 15820652 — Seeing, hearing, reading, or thinking about a yawn can start a yawn. Brain scans showed linked activity.
• "An investigation of auditory contagious yawning." (2009) — PMID 19679768 — Yawn sounds raised the urge to yawn more than control sounds, linked to empathy scores.
• "Contagious yawning, empathy, and their relation to prosocial behavior." (2018) — PMID 29771564 — In 171 and 333 people, only yawn spreading was linked to empathy, not helping.
• "Individual variation in contagious yawning susceptibility is highly stable and largely unexplained by empathy or other known factors." (2014) — PMID 24632594 — In 328 people, differences were very stable and not explained by empathy once age was counted.
• "Contagious yawning in autistic and typical development." (2010) — PMID 20840244 — In 120 children aged 1 to 6, yawn spreading rose a lot at about age 4.
• "A Neural Basis for Contagious Yawning." (2017) — PMID 28867202 — Holding back raised the urge and changed yawn shape, but not how much yawns spread.
• "Social Presence Diminishes Contagious Yawning in the Laboratory." (2016) — PMID 27112374 — Being told someone is there, or someone really being there, reduced yawn spreading.
• "Contagious yawning in virtual reality is affected by actual, but not simulated, social presence." (2019) — PMID 30670744 — A real tester in the room reduced yawns in VR. Virtual cameras and avatars did not.
• "Dogs catch human yawns." (2008) — PMID 18682357 — 21 of 29 dogs yawned at a human yawn, none at control moves.
• "Do dogs (Canis familiaris) show contagious yawning?" (2009) — PMID 19452178 — Only 1 of 15 dogs clearly yawned back.
• "Contagious yawning, social cognition, and arousal: an investigation of the processes underlying shelter dogs' responses to human yawns." (2014) — PMID 23670215 — 12 of 60 shelter dogs yawned only to yawns, linked to stress hormone levels.
• "Contagious yawning is not a signal of empathy: no evidence of familiarity, gender or prosociality biases in dogs." (2020) — PMID 32075525 — Dogs catch yawns, but closeness, sex, and kindness did not matter.
• "Familiarity bias and physiological responses in contagious yawning by dogs support link to empathy." (2013) — PMID 23951146 — 25 dogs yawned more for their owner. Heart rate did not differ.
• "Contagious yawning in domestic dog puppies (Canis lupus familiaris): the effect of ontogeny and emotional closeness on low-level imitation in dogs." (2013) — PMID 23076724 — In 35 puppies, closeness did not matter. Only dogs over 7 months caught yawns.
• "Ingroup-outgroup bias in contagious yawning by chimpanzees supports link to empathy." (2011) — PMID 21494669 — 23 chimps yawned more at yawns from chimps they knew.
• "Chimpanzees show a developmental increase in susceptibility to contagious yawning: a test of the effect of ontogeny and emotional closeness on yawn contagion." (2013) — PMID 24146848 — In 33 orphan chimps, young ones caught yawns and babies did not. Closeness did not matter.
• "Contagious yawning in gelada baboons as a possible expression of empathy." (2009) — PMID 19889980 — Yawns spread more between monkeys that cleaned each other's fur more.
• "Social modulation of contagious yawning in wolves." (2014) — PMID 25162677 — Wolves caught yawns more from close pack members.
• "Contagious Yawning in African Elephants (Loxodonta africana): Responses to Other Elephants and Familiar Humans." (2020) — PMID 32457923 — 3 of 7 elephants yawned at a known keeper's yawn.
• "Experimental evidence of contagious yawning in budgerigars (Melopsittacus undulatus)." (2015) — PMID 26012708 — First test proof of yawn spreading in a non-mammal.
• "No Experimental Evidence For Yawn Contagion In Galahs (Eolophus Roseicapilla)" (2025) — DOI: 10.26451/abc.12.02.01.2025 — 15 galahs showed no yawn spreading in two tests.
• "Interspecific Contagious Yawning in Humans." (2022) — PMID 35892558 — 296 people said they yawned at many animals' yawns. The kind of animal did not matter.
• "Yawning Is More Contagious in Pregnant Than Nulliparous Women : Naturalistic and Experimental Evidence." (2021) — PMID 34255275 — Pregnant women caught yawns more, in tests and in daily settings.
• "Development of fetal yawn compared with non-yawn mouth openings from 24-36 weeks gestation." (2012) — PMID 23185638 — In 15 babies before birth, yawns could be told apart from open mouths.
• "Fetal yawning and mouth openings: Frequency, developmental trends, and association with birth weight." (2026) — PMID 41739743 — In 32 babies before birth, yawns were under 5 per hour. Yawning before birth is a gap for the cooling idea.
• "Prenatal behavioral contagion through maternal yawning and fetal resonance." (2026) — PMID 42092355 — Babies before birth yawned more after the mother yawned, not in the control.
• "Yawning throughout life." (2010) — PMID 20357459 — Adult yawning follows sleepiness, except just after waking.
• "Yawning: no effect of 3-5% CO2, 100% O2, and exercise." (1987) — PMID 3120687 — Oxygen, carbon dioxide, and exercise did not change yawning.
• "Is yawning an arousal defense reflex?" (1989) — PMID 2558182 — A review that saw yawning as a reflex to fix low oxygen in the brain.
• "Why do we yawn?" (2010) — PMID 20382180 — Body role ideas lack proof. The message idea gets more support.
• "Why do we yawn? Primitive versus derived features." (2011) — PMID 20883719 — A reply: the message idea also lacks clear proof, and the first role is likely in the body.
• "Why do we yawn? The importance of evidence for specific yawn-induced effects." (2011) — PMID 21168437 — A reply back: the only clear effect shown so far is that yawns spread.
• "Why contagious yawning does not (yet) equate to empathy." (2017) — PMID 28735879 — Proof for a link between yawn spreading and empathy does not match and gives no answer.
• "Yawning as a Brain Cooling Mechanism: Nasal Breathing and Forehead Cooling Diminish the Incidence of Contagious Yawning" (2007) — DOI: 10.1177/147470490700500109 — Nose breathing brought yawn spreading to zero. A cold forehead brought it to 9%.
• "Manipulating neck temperature alters contagious yawning in humans." (2019) — PMID 31022409 — Cooling the neck reduced the urge to yawn and the number of yawns.
• "Contagious yawning and seasonal climate variation." (2011) — PMID 21960970 — 45% yawned at yawn pictures in winter at 22°C, 24% in early summer at 37°C.
• "A thermal window for yawning in humans: yawning as a brain cooling mechanism." (2014) — PMID 24721675 — 18.3% reported yawning in winter at 1.4°C, 41.7% in summer at 19.4°C.
• "Yawning and stretching predict brain temperature changes in rats: support for the thermoregulatory hypothesis." (2010) — PMID 21031034 — Rat yawns came as brain heat rose, then heat went back to normal.
• "Yawning reduces facial temperature in the high-yawning subline of Sprague-Dawley rats." (2017) — PMID 28049450 — Rat ear and eye heat dropped 0.3 to 0.4°C 10 seconds after yawns.
• "Thermal imaging reveals sizable shifts in facial temperature surrounding yawning in budgerigars (Melopsittacus undulatus)." (2017) — PMID 29435482 — In 13 budgies, face heat dropped 0.36°C 10 to 20 seconds after yawns.
• "The thermoregulatory theory of yawning: what we know from over 5 years of research." (2012) — PMID 23293583 — A review backing the cooling idea: five years of tests matched, none found the opposite.
• "Yawning, a thermoregulatory mechanism during fever? A study of yawning frequency and its predictors during experimentally induced sickness." (2017) — PMID 28939427 — Yawning rose during a test fever, but was not clearly linked to body heat rise.
• "Brain size and neuron numbers drive differences in yawn duration across mammals and birds." (2021) — PMID 33958700 — In 1,291 yawns from 101 kinds, bigger brains with more cells had longer yawns, not explained by body size alone.
• "Emotional contagion in children with autism spectrum disorder varies with stimulus familiarity and task instructions." (2020) — PMID 30924430 — The gap got smaller when children looked at the eyes or parents were the yawners.