When you go to sleep, do you ever feel yourself trying to yawn, but you can’t? Strangely enough, there’s more to a yawn than meets the eye. Sure, we all do it, especially when we’re tired. But what is the purpose of it, and what should we know about yawning that we might not already? Well for one, it’s a more important bodily function than many of us think. For example, if you’ve ever noticed your eyes watering when you yawn, this is likely because the muscles that generate tears are stretched and tightened.

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You likely already know that it’s incredibly contagious—after all, we can find ourselves sneezing by just thinking about it, let alone sneezing right after we see someone else do it. In other words, it isn’t just something we do when we’re bored or sleepy. Here’s why yawning is much bigger than that.

Why is yawning so important for us?

The primary reason we need to yawn so often is to keep our brain temperature at cooler levels. When brain temperatures start to overheat or rise above-average levels, yawning helps regulate and neutralize these temperatures. If you’re in the same environment as someone who’s yawning and you start yawning in response, it’s because you both have similar brain temperatures from being in that space. Yawning also allows your body to stretch itself out, and increases blood flow in your face and expands joints, tissues and muscles.

While research about yawning has continued to evolve over centuries, at least one study poses that contagious yawning relates to how our emotions are subconsciously tied to the emotions of those around us. In fact, theories about yawning go as far back as Ancient Greece. Hippocrates believed that yawning was a way to release air that would otherwise cause a fever. Another theory, known as the Thompson Cortisol Hypothesis, suggests that the root of our yawning is traced to increases in cortisol, the stress hormone.

What is frequent incomplete yawning?

Of course, there are some instances where yawning can be an ongoing issue. One example is when you can’t get a good, complete yawn, which happens when you’re about to yawn but your mouth suddenly closes before you can get it out.. Frequent incomplete yawning can also be a sign of stress and/or anxiety, which will make it difficult for muscles in your face and elsewhere in your body to stretch and relax properly.

Do you feel like you can’t yawn properly? If so, it’s a possible sign of dysfunction in your nervous system. Being unable to finish a yawn indicates that it’s not expelling energy from your nervous system normally, which can lead to an unhealthy accumulation of that energy. When you feel calm, comfortable, and with relatively no stress, it’s easier for your nervous system to let go of that energy, since you won’t be feeling the same kind of arousal you would while under stress.

How can you make yourself yawn when you can’t?

Some people may struggle with yawning excessively. If you’re one of those, you’ve probably looked on Wikihow to see how deep breathing, staying hydrated, cooling yourself down, going outdoors, and getting more sleep can all help you yawn less frequently. But what if you’re experiencing the opposite, where you want to yawn so badly, but can’t? Again, this is indicative of your autonomic nervous system not functioning as it should. The frustration you feel from not completing a yawn properly is called: anhedonia.

If you don’t yawn when someone else does, what then? Well, we hate to break it to you, but it could be a sign that you’re a psychopath. Research suggests that those who exhibit psychopathic traits are less likely to yawn when someone else does. This is because psychopathy is defined partially by a lack of empathy, and empathy is the primary emotion behind why yawning is so contagious. However, just because you aren’t yawning at the same time as someone immediately near you doesn’t necessarily mean you’re a psychopath, since we don’t normally yawn when we see a complete stranger do so.