Why do we yawn?
We yawn mostly around sleep, in the hour after waking up and the hour before going to bed (Provine, 1987), and when we see someone close to us yawn. It isn't a lack of oxygen: breathing more of it changes nothing (Provine, Tate and Geldmacher, 1987). A yawn lasts 5.9 seconds on average; its exact purpose is still debated.
Simplified diagram, not to scale. Dotted curves are estimates based on the studies cited; they show a relative level, from 0 to 100, and the percentages in the notes are measured.
Why do we yawn?
A yawning face, with its brain temperature according to a hypothesis. Choose a situation, then tap a label on the drawing to find out what it is.
Sources: times of day and duration (Provine, 1986 and 1987; Zilli et al., 2007); oxygen (Provine, Tate and Geldmacher, 1987); contagion (Norscia and Palagi, 2011; Helt et al., 2010; Bartholomew and Cirulli, 2014); temperature (Massen et al., 2014; Gallup and Eldakar, 2011; Gallup and Gallup, 2007); rat brain (Shoup-Knox et al., 2010). Drawing not to scale; yawns shortened; curves: estimates.
Keyboard: 1 to 3 situations, Space pause, L slow motion, R restart, ← → previous or next step.
Frequently asked questions about yawning
Do we yawn because we lack oxygen?
No, we don't yawn because we lack oxygen. Volunteers who breathed pure oxygen, or air with more carbon dioxide, yawned neither more nor less; exercise that doubled their breathing changed nothing either (Provine, Tate and Geldmacher, 1987). Yet this idea is still very widespread.
Why is yawning contagious?
We still don't really know why yawning spreads. What we do know: people catch a yawn from someone close more often than from a mere acquaintance (Norscia and Palagi, 2011), contagion appears around age 4 (Helt et al., 2010), and each person keeps their own tendency, with no clear link to empathy measured by questionnaires (Bartholomew and Cirulli, 2014). Thinking about yawning or reading about it is also enough to trigger one (Provine, 1986).
Do babies yawn before birth?
Yes, babies already yawn in the womb, from about the 11th week of pregnancy. In 32 fetuses aged 23 to 31 weeks followed by ultrasound, there were on average 3.63 yawns per hour (Menin et al., 2026). At this age, it isn't contagion: the fetus doesn't see anyone yawn.
Do animals yawn too?
Yes, many animals yawn, especially mammals. Across 19 mammal species, the longest yawns went with the heaviest brains and those richest in neurons (Gallup, Church and Pelegrino, 2016). In humans, a yawn lasts 5.9 seconds on average (Provine, 1986).
Is yawning a lot a sign of something serious?
Most often, yawning a lot means you're short on sleep or bored. Some medicines can also make you yawn more. If you yawn much more than usual for no clear reason, especially with other symptoms, it's best to talk to a doctor (MedlinePlus).
True or false?
We yawn because the body lacks oxygen.
False. Breathing pure oxygen, or air with more carbon dioxide, didn't change the number of yawns (Provine, Tate and Geldmacher, 1987).
Babies already yawn before they're born.
True. The fetus yawns from about the 11th week of pregnancy; between 23 and 31 weeks, there were on average 3.63 yawns per hour (Menin et al., 2026).
We catch a yawn from someone close more often than from a stranger.
True. The contagion rate was 0.85 with family, 0.52 with friends, 0.39 with acquaintances, and lower still with strangers (Norscia and Palagi, 2011).
This page as text
The same information as the charts, to read without animation: for each chart, the values at the main moments, then the notes with their level of evidence.
What time of day do we yawn the most?
Mostly in the hour after waking up and the hour before going to bed, little in the middle of the day. Estimated curves, for a day of 17 hours awake.
| Hours since waking up | Morning person (dotted) | Evening person (dotted) | What happens |
|---|---|---|---|
| Wake-up | 75 | 100 | On waking |
| 4 h | 15 | 28 | after waking up |
| 8 h | 11 | 14 | after waking up |
| 12 h | 16 | 15 | after waking up |
| Bedtime | 95 | 88 | At bedtime |
Key points
- The wake-up peak (Up to 1 h 01 after waking up, Shown in humans)
Students recorded their yawns for a week: they yawned the most in the hour after waking up and the hour before going to bed. On waking, people also often stretch while yawning. Source: Provine, Hamernik and Curchack, "Yawning: relation to sleeping and stretching in humans", Ethology, 1987 - About 6 seconds (All day, Shown in humans)
A yawn lasts 5.9 seconds on average. In people asked to think about yawning, about 68 seconds passed between two yawns: thinking about it, or reading about it, is enough to make you yawn. Source: Provine, "Yawning as a stereotyped action pattern and releasing stimulus", Ethology, 1986 - Evening people, in the morning (Up to 6 h after waking up, Shown in humans)
In 16 adults followed for 3 days, evening people yawned more than morning people, especially in the morning; in everyone, yawns increased as bedtime approached. Source: Zilli, Giganti and Salzarulo, "Yawning in morning and evening types", Physiol Behav, 2007 - Not for oxygen (From 4 h to 14 h after waking up, Shown in humans)
Breathing pure oxygen, or air with more carbon dioxide, didn't change the number of yawns. Neither did exercise that doubled breathing: yawning isn't mainly for breathing. Source: Provine, Tate and Geldmacher, "Yawning: no effect of 3-5% CO2, 100% O2, and exercise", Behav Neural Biol, 1987 - Even before birth (All day, Shown in humans)
The fetus yawns from the 11th week of pregnancy. In 32 fetuses aged 23 to 31 weeks, there were on average 3.63 yawns per hour. Source: Menin et al., "Fetal yawning and mouth openings: Frequency, developmental trends, and association with birth weight", PLoS One, 2026 - Estimated curves (All day, Hypothesis)
The times of day come from the studies; the height of the curves is an estimate, to compare the two profiles.
Why do we yawn when someone else yawns?
Yawning "spreads" mostly between people who are close: more often and faster with family than with mere acquaintances. Estimated curves, as a share of yawns caught.
| Hours since waking up | Family (dotted) | Friends (dotted) | Acquaintances (dotted) | What happens |
|---|---|---|---|---|
| Yawn seen | 0 | 0 | 0 | The moment you see someone yawn |
| 1 min | 68 | 40 | 17 | after seeing someone yawn |
| 2 min | 80 | 49 | 30 | after seeing someone yawn |
| 3 min | 85 | 52 | 39 | after seeing someone yawn |
| 4 min | 85 | 52 | 39 | after seeing someone yawn |
| 5 min | 85 | 52 | 39 | after seeing someone yawn |
Key points
- The closer you are, the more you yawn (Throughout, Shown in humans)
In 109 adults observed in everyday life, the contagion rate was 0.85 with family, 0.52 with friends, and 0.39 with acquaintances, and lower still with strangers. Neither sex nor nationality changed this result. Source: Norscia and Palagi, "Yawn contagion and empathy in Homo sapiens", PLoS One, 2011 - Slower with less close people (From 1 to 3 min, Shown in humans)
Caught yawns were counted for 3 minutes. With acquaintances or strangers, the response also came later. Source: Norscia and Palagi, "Yawn contagion and empathy in Homo sapiens", PLoS One, 2011 - From age 4 (Throughout, Shown in humans)
In 120 children aged 1 to 6, yawn contagion rose sharply at age 4. Source: Helt et al., "Contagious yawning in autistic and typical development", Child Dev, 2010 - Less with age, but mostly depends on the person (Throughout, Shown in humans)
In 328 people, contagious yawning decreased with age, but age explained only 8% of the differences. Each person kept their own tendency from one time to the next, with no clear link to empathy. Source: Bartholomew and Cirulli, "Individual variation in contagious yawning susceptibility is highly stable and largely unexplained by empathy or other known factors", PLoS One, 2014 - Why the contagion? (Throughout, Hypothesis)
A link with empathy is often suggested, since contagion follows closeness; but other studies don't find it. The question remains open. - Estimated curves (Throughout, Hypothesis)
The rates at 3 minutes come from the study cited; the shape of the curves before 3 minutes is an estimate.
Do we yawn more when it's hot or cold?
We yawn less in extreme cold and intense heat, more when the weather is mild: a temperature "window." Estimated curve based on two studies, as the share of passersby who yawn when they see someone yawn.
| Hours since waking up | Passersby who yawn when they see someone yawn (dotted) | What happens |
|---|---|---|
| 0 °C | 15 | outside |
| 10 °C | 32 | outside |
| 20 °C | 43 | outside |
| 30 °C | 36 | outside |
| 40 °C | 20 | outside: almost body temperature |
Key points
- Cold holds back yawning (Up to 20 °C, Shown in humans)
In 120 passersby in Vienna, 18.3% said they yawned when seeing someone yawn at 1.4 °C, in winter, versus 41.7% at 19.4 °C, in summer. Source: Massen et al., "A thermal window for yawning in humans: yawning as a brain cooling mechanism", Physiol Behav, 2014 - Intense heat too (From 20 °C, Shown in humans)
In a desert city in the United States, 45% of passersby yawned while looking at photos of yawns in winter, around 22 °C, versus 24% in early summer, around 37 °C. Source: Gallup and Eldakar, "Contagious yawning and seasonal climate variation", Front Evol Neurosci, 2011 - Nose breathing, cool forehead (At all temperatures, Shown in humans)
In a study, about 48% of people yawned when seeing someone yawn while breathing normally or through the mouth, none while breathing through the nose. With a cold pack on the forehead, 9% yawned, versus 41% with a warm or hot pack. Source: Gallup and Gallup, "Yawning as a brain cooling mechanism: nasal breathing and forehead cooling diminish the incidence of contagious yawning", Evol Psychol, 2007 - In rats, the brain cools down (At all temperatures, Seen in animals)
In rats, brain temperature rose just before a yawn, then dropped afterward. Source: Shoup-Knox et al., "Yawning and stretching predict brain temperature changes in rats", Front Evol Neurosci, 2010 - Big brain, long yawn (At all temperatures, Seen in animals)
Across 19 mammal species, the longest yawns went with the heaviest brains and those richest in neurons. Source: Gallup, Church and Pelegrino, "Yawn duration predicts brain weight and cortical neuron number in mammals", Biol Lett, 2016 - Cooling the brain? A hypothesis (At all temperatures, Hypothesis)
These results support the idea that yawning cools the brain, but it remains a hypothesis; other ideas, such as staying awake or a signal between people who are close, are debated. - Estimated curve (At all temperatures, Hypothesis)
The four measured points come from two studies done in different cities and seasons; the curve connecting them is an estimate.
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