Why Do We Yawn?

It’s 3 p.m., and you’re sitting at your desk, hoping that the rest of the day goes by quickly so you can finally leave the office and relax. As you stare at the computer screen, trying to make sense of the numbers, you find yourself stifling a yawn. Over the next two hours, you seem to be yawning uncontrollably — but once you’re in the car and on the way home, it stops.

What gives? Why is it that you yawn when you’re bored, tired, or strangest of all, when you see someone else yawning? There’s a good chance that you’re yawning just reading this, too.

The fact is, scientists don’t really know why humans yawn. They’ve been unable to find any clear physiological effect of yawning or explanation of why it happens when it does. It’s also a mystery why yawns are “contagious,” and occur even between humans and animals. It’s true: When your dog sees you yawn, it’s likely they will yawn, too.

That being said, there are some theories about this behavior — and a few theories that scientists have ruled out.

Yawning: The Brain’s Air Conditioning?

Until the late 1980s, scientists theorized that yawning was the body’s way of taking in more air in response to reduced oxygen levels in the blood. However, a series of experiments conducted on college students disproved this theory, revealing that yawning has no effect on blood oxygen levels at all.

With the oxygen theory disproved, researchers began looking for other reasons for yawning. In 2014, a study by researchers at SUNY College in Oneonta, NY published in the journal Physiology and Behavior revealed that yawning appears to be a way for the brain to regulate its temperature. Taking in excess air helps cool the brain, ensuring that it remains at the optimum temperature.

As the researchers explained, when we are tired, bored, or experiencing stress, the brain gets warmer. Basically, as the brain slows down, it heats up, and yawning helps cool it down so it remains in homeostasis and doesn’t overheat. The theory is supported in part because yawning typically only occurs when ambient temperatures fall within a certain range: The colder it is, the less likely we are to yawn.

The researchers suspect that cooling the brain is important for improving its arousal and alertness. That could explain why we yawn when we’re bored: When your brain isn’t “overheating,” it’s easier to stay alert and focused on the task at hand. In fact, some researchers also hypothesize that the physical act of yawning is designed to wake your body. Yawning forces your lungs to stretch and increases blood flow, which can increase alertness.

Keeping you awake and alert may also be why you yawn when you are sleepy. Warm temperatures tend to make us tired in and of themselves, and when you’re tired and your brain is slowing down, yawning may be your brain’s subconscious way of trying to keep you awake. This could also explain why most of us yawn when we first wake up — it’s our brain’s way of “jumpstarting” us back into a state of alertness.

So Why Are Yawns Contagious?

So if yawns are meant to keep your brain cool, why is it that once you start, so does everyone around you — or vice versa?

There is some evidence that contagious yawns are actually a sign of empathy. Brain imaging studies revealed that when someone yawns because they see another person yawning, it involves parts of the brain known to be involved in social functions. Some scientists believe that the more empathetic you are, the more likely you are to “catch” yawning from others.

However, this theory is based on a very small study, so the results can’t be generalized. So don’t worry — if you don’t typically “catch” yawns, that doesn’t mean you’re a psychopath.

Other scientists suspect that contagious yawns have slightly more primal origins. Because yawns trigger brain arousal and alertness, it’s possible that they are contagious to serve as a type of warning system to others.

Simultaneous yawning synchronizes the group’s mental state, better positioning it to respond to threats. Or, it could just be that when one person’s brain temperature is rising, so are others’, and seeing a yawn is simply a subconscious trigger to cool it down.

Whatever the reason yawns are contagious, it can make for some amusing situations as they travel around the room. If you find yourself yawning too much, head to bed and get some shuteye, or if that’s not possible, stop by practicing deep breathing, breaking up your routine with a short walk, or cooling down with a chilled drink or snack.