Why Is Yawning Contagious? What the Studies Actually Show
Reading about yawning is enough to make many people yawn. Scientists have tested why, and the answers are less tidy than the popular explanations.
Yawning is contagious because seeing, hearing or even reading about a yawn can trigger the same action in the brain of an onlooker, and it spreads most readily between people who are close. A 2011 observational study found yawns passed most often between relatives, then friends, then acquaintances and least between strangers. Why we yawn at all is less settled: the popular oxygen-shortage idea failed experimental tests, and the brain-cooling hypothesis has support but is still debated.
Contagious yawning appears in children from around age four and in chimpanzees, and there is some evidence that dogs catch human yawns.
Why do we yawn in the first place?
Nobody knows for sure, but several explanations have been tested. A yawn is a long, wide opening of the mouth with a deep breath in, a stretch of the jaw and a shorter breath out, and many vertebrates do something similar.
The leading ideas fall into three groups:
- State change: yawning tends to happen around transitions, such as waking up, getting sleepy or becoming bored, and may help the brain shift its level of alertness.
- Brain cooling: a yawn draws in a large breath of air and increases blood flow in the head, which may help cool the brain.
- Social signal: in social species, a yawn may carry information about the group’s state to others.
These are not mutually exclusive, and the evidence for each is mixed. Yawning is closely tied to sleep and waking, a topic we cover in why we need sleep.
Is yawning caused by a lack of oxygen?
No, the evidence does not support that. The idea that we yawn to get more oxygen or blow off carbon dioxide was tested in a 1987 study by Robert Provine and colleagues in the journal Behavioral and Neural Biology. Breathing air with 3% to 5% carbon dioxide, breathing 100% oxygen and doing exercise produced no effect on yawning, as the paper’s title states.
If yawns were a fix for low oxygen, pure oxygen should have reduced them and extra carbon dioxide should have increased them. Neither happened, which is why most researchers dropped the oxygen explanation.
What is the brain-cooling hypothesis?
The brain-cooling hypothesis says that yawning helps regulate the temperature of the brain. A yawn stretches the jaw and pulls in a deep breath of air, which may bring cooler blood toward the brain.
In a 2007 study in Evolutionary Psychology, Andrew and Gordon Gallup showed volunteers videos of people yawning and changed the conditions:
| Condition | Share who yawned contagiously |
|---|---|
| Normal or mouth breathing | About 48% |
| Breathing only through the nose | 0% |
| Warm or room-temperature pack on the forehead | 41% |
| Cold pack on the forehead | 9% |
The authors argued that nasal breathing and a cold forehead both cool the brain, so there is less need to yawn. A 2016 study in Biology Letters by Gallup and colleagues found that across mammal species, longer average yawns go with heavier brains and more neurons in the cortex, which fits the idea that yawns serve the brain. These are suggestive results from small or comparative studies, and other researchers interpret them differently.
Why do yawns spread between people?
Yawns seem to spread through social connection. In a 2011 study in PLoS ONE, Ivan Norscia and Elisabetta Palagi recorded yawns among adults in everyday settings for a year. Only the social bond between people predicted contagion: it was highest among relatives, then friends, then acquaintances, and lowest among strangers. Strangers also responded with a longer delay.
Because the same ranking shows up in measures of empathy, many researchers link contagious yawning to empathy. The evidence is mixed, though. A 2014 PLoS ONE study of 328 people found that each person’s tendency to catch yawns was very stable across sessions, but that empathy, time of day and intelligence did not predict it once age was accounted for. Older participants caught fewer yawns, yet age explained only about 8% of the variation, and most of the differences between people remained unexplained.
Do animals catch yawns?
Some do. Chimpanzees catch yawns from each other, a finding first reported in 2004 in the Proceedings of the Royal Society B. A 2011 study of 23 chimpanzees found that they yawned more when watching videos of familiar group members yawning than unfamiliar chimps, the same in-group pattern seen in people.
Dogs may catch human yawns. In a 2008 study in Biology Letters, 21 of 29 dogs yawned after watching a person yawn, while none yawned at mouth movements that were not yawns. Later studies of dogs have given mixed results, so the effect is not settled. Many animals yawn without any contagion at all, and sleep-related behavior varies widely across species, as we describe in how animals sleep.
When do children start catching yawns?
Children do not catch yawns as babies. A 2010 study in Child Development tested 120 children aged 1 to 6 and found a sharp increase in contagious yawning at about 4 years old. Babies and toddlers yawn spontaneously but the contagious kind develops later. The same study found that children with autism spectrum disorders caught yawns less often than other children of the same age.
Bottom line
Yawns are contagious, spreading most among relatives and friends and least among strangers, and they become contagious in children around age four. The oxygen-shortage explanation failed a 1987 test, while brain cooling has some experimental support but remains debated. Chimpanzees catch yawns from familiar group members, and dogs may catch them from people, though dog studies disagree.
FAQ
Why does reading about yawning make me yawn?
Contagious yawning can be triggered by seeing, hearing or even thinking about a yawn. Many people find themselves yawning while reading about it, though not everyone is equally susceptible.
Does not catching yawns mean someone lacks empathy?
No. A 2014 study of 328 people found that empathy did not predict who caught yawns once age was accounted for, and most of the difference between people was unexplained.
Do fish and birds yawn?
Many vertebrates show yawn-like gaping, including some birds and fish. Contagious yawning, though, has mainly been reported in social mammals such as humans and chimpanzees.
Can you stop a yawn?
Many people can suppress a yawn partly. In the 2007 Gallup study, breathing through the nose during yawning videos stopped contagious yawning in that group.
