Why Do Yawns Spread From One Person to Another?

1. Even Reading or Thinking About a Yawn Can Start One

In a 1986 paper, the psychologist Robert Provine reported that seeing someone yawn is a powerful trigger, and that simply thinking about yawning, or reading about it, could also set off a yawn[2]. So a yawn does not have to come in through the eyes as a picture of a face. The idea of one can be enough.

That already makes a catching yawn odd. Whatever a yawn is, something in the brain seems to respond to the idea of it. The next question is whether everyone responds equally.

2. Babies and Toddlers Do Not Seem to Catch Yawns

Babies yawn, of course, and so do toddlers. But catching a yawn from someone else looks like a later skill. Two researchers, Millen and Anderson, asked parents to keep a one-week log of their young child’s yawns. None of the log entries described a yawn the child had caught. In a second part of the study, infants and preschoolers were shown many pictures of yawning and a repeated video of their own mother yawning. There was no sign of contagious yawning[3].

The authors pointed out that the mother is someone with a strong, positive bond to the child, so a lack of closeness does not explain the result. Another study that watched people in everyday places put the starting point of yawn contagion at around 4 to 5 years old[4]. Exact ages differ from study to study, so treat “around 4 or 5” as a rough guide, not a fixed birthday for the skill.

3. People Who Are Close to You Set Off Your Yawns More Easily

Among adults, who yawns after whom? Norscia and Palagi spent a year watching 109 adults from Europe, North America, Asia and Africa in everyday settings, recording each yawn and how the person nearby reacted. The pattern followed how close the two people were. Relatives caught yawns most, then friends, then acquaintances, then strangers. Strangers and acquaintances also took longer to yawn back. Whether the person was male or female, and which country they came from, did not make a significant difference[4].

A later team tested this with yawns that could be heard but not seen, so the listener could not be catching it by looking at a face. They studied 294 such yawns collected from 2,001 yawning episodes during 2010 to 2019. Yawns still passed more readily between friends and family than between strangers and acquaintances[5]. That result is hard to explain by “you simply look at your friends more.”

4. Chimpanzees Yawned More at Videos of Chimps They Knew

Back to the chimpanzee at the little box. In that study, 23 adult chimpanzees from two groups watched videos of chimps from their own group and of chimps they had never met, either yawning or resting. They yawned more after the yawning video of a familiar chimp than after the resting video of the same chimp, and more than after a stranger’s yawn[1]. The yawns of unfamiliar chimps did not produce a statistically clear rise. The researchers noted that the group might have been too small to spot a small effect for strangers.

So the closer-is-stronger pattern is not only human. Whether it appears for the same reason in chimps and in people is a harder question.

5. Does Catching a Yawn Mean You Care? Scientists Disagree

The “closer is stronger” results led many researchers to suggest that yawn contagion is a sign of empathy, meaning a shared feeling between two individuals. Norscia and colleagues describe their 2020 results as supporting this “emotional bias” idea, partly because the effect stayed strong even with no faces to look at[5].

Researchers disagree on how far that goes. A 2017 review by Massen and Gallup went through the evidence on empathy scores, familiarity, sex, psychological conditions, child development and brain imaging. It concluded the evidence is inconsistent and inconclusive, and that confounding factors such as how much someone pays attention to a face need to be controlled[6].

Two examples show why caution makes sense. In Japan, researchers used an eye tracker to make sure children with autism spectrum disorder looked at the yawning face. When they did, those children yawned more after yawning videos than after other videos, just as other children did. The authors suggested that earlier reports of fewer contagious yawns in autism may partly reflect less spontaneous looking at faces. They also cautioned that this cannot explain every earlier result, since the absence has also been reported with yawning sounds[7]. And in dogs, a study that combined earlier data on 257 dogs with a new experiment on 32 dogs found no sign that dogs catch yawns more from a familiar person or from someone friendly. Dogs do yawn contagiously, but the researchers argued it is not driven by empathy[8].

The honest summary is that contagion does track social closeness, but whether “caring” is the cause is still open.

6. Heat May Change How Easily a Yawn Spreads

A second idea asks what a yawn is for. One proposal is that yawning helps cool the brain, because a big breath of air and the stretching of the face may change the temperature of blood heading to the head[9]. If that is right, a yawn should come less easily when the air is already very hot.

A team in Tucson, Arizona, tested this outdoors. Passersby were shown pictures of people yawning. In winter, with air at about 22 °C (72 °F), 45% of them yawned. In early summer, at about 37 °C (99 °F), only 24% did[10]. The authors took this as support for the brain-cooling idea. It is a single desert study, and it does not yet separate heat from other differences between seasons. The review I used also notes that similar experiments can be muddied by other effects, such as sleepiness[9]. Treat it as an interesting clue, not a final answer.

7. Try It at Home: Keep a One-Week Yawn Log

You can run a gentle version of the research with nothing but a notebook. For a week, whenever you yawn, write one line: where you were, and whether someone nearby had just yawned. If you like, note who it was: a family member, a friend, a classmate.

A few things to keep in mind. You will not be able to tell for sure why any single yawn happened, since you might simply be tired. A week of notes from one person cannot prove what the studies above could not settle. But you may spot a pattern, and you will see for yourself how hard it is to separate “caught it” from “was already sleepy.” That difficulty is a large part of why scientists are still arguing.

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