Whether it’s early in the morning, late at night, during a slump in the middle of the day, or even looking at someone else doing it, a yawn can sneak up on you without warning. The worst part: You can’t do anything about it. Most people think that yawning is a symptom of drowsiness, but it can actually occur for a variety of different reasons. So, why do we yawn, and is it really contagious?

Increase oxygen flow

Tired woman sitting at laptop and yawning
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It was long believed that yawning was a respiratory function. When your body is running low on oxygen, a yawn is triggered to force a deep inhale and exhale. This increases oxygen levels in the bloodstream, and the yawn itself raises your heartbeat to pump the oxygen-rich blood throughout the body.

While this theory is still possible, or is, perhaps, one aspect of yawning, it’s not the whole story. If the purpose of yawning is to bring in more oxygen, then shouldn’t people yawn more when they’re performing oxygen-depriving actions like manual labor or exercising? Researchers have found very little evidence that oxygen-deprived people yawn more frequently, which has led them to another theory.

Temperature regulation

Small dog sitting on floor, yawning
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Instead of oxygen deprivation, researchers now believe that the primary function of yawning is regulating temperature. Your brain is the most energy-hungry organ in your body. It uses about 40% of your total metabolic energy. All that energy means that your brain tends to run hot and needs some way to cool down. Your brain uses yawning like your computer uses fans.

During a yawn, cold air is brought in through the mouth. The muscles in your jaw and around your skull contract and stretch, which increases blood circulation in the area. The air cools the blood, and the increase in heart rate pumps the cooler blood to your brain. A cooler brain is a more alert brain.

You yawn more when it’s cold

Your body knows how to be efficient. If the surrounding air is cooler, yawning will be more effective. It might sound strange, but studies have shown that people yawn more frequently in cooler temperatures. People yawned 21% more often when the outside air was 70 degrees Fahrenheit versus 98 degrees (body temperature). Similar results were also found with other species of animals.

Yawn triggers

Woman in white sitting at laptop computer and yawning
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There are dozens of triggers associated with yawning. Of course, there are the obvious triggers like boredom and drowsiness, when your brain needs to be stimulated, but yawning can also be triggered by other events like anxiety, hunger, or even a change of activity. Any time your brain needs some extra focus, it will trigger a yawn for a refreshing cool down.

Needing extra focus is also true in times of tension. Police officers frequently report yawning before entering into a difficult situation, and it’s not uncommon for skydivers to yawn right before a jump. They’re not bored; they just need some extra focus.

It’s contagious

Man sitting at desk in front of books, yawning with hand over mouth
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You don’t need a scientific study to tell you that yawning is contagious. Even watching a video or reading about yawning is enough to trigger one. You’ve probably yawned at least once just from reading this! Because so little is known about yawning, experts can only speculate why it’s so contagious.

All vertebrates yawn, but only three species yawn contagiously: humans, chimpanzees and wolves/dogs. Every species that yawns contagiously are animals that live and work in packs. One theory suggests that yawning is a form of communication used to display the alertness of the group. It’s contagious so that the message can be passed along throughout the pack. You don’t want to be hunting when a member of your group isn’t alert.

One of the most common theories is that the contagiousness of yawning is linked to empathy. If you see someone yawn, you’ll yawn out of empathy. The closer you are with the yawning person, the more contagious it tends to be.

Who knows?

Although there are plenty of theories regarding the purpose, triggers and contagiousness of yawning, none of them is certain. Because yawning is a normal function and doesn’t hurt anything, it’s unlikely that research on it will happen any time soon. There are many more pressing matters in the scientific and medical communities. It could be any one of the theories mentioned or even a combination of a few. Nobody knows for sure.