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Sometimes when you’re up past your bedtime, you can just feel the sleep  deprivation in your eyeballs. And you’ve likely found some relief  by rubbing those sleepy sockets.

But have you ever wondered why  it feels so darn good to do it? Two reasons. Rubbing your eyes helps keep them moist,  but it also affects your heart rate.

Our eyes depend on tears. Sure, sobbing because you’ve  just seen a long lost dog reunited with its family  might not feel super helpful. But our body doesn’t just produce  tears when we’re emotional.

Throughout the day we’re secreting basal tears, which create a smooth film  on the surface of our eyes. These tears have a lot of important jobs, from helping us see properly to  protecting us from infections. But when you’re tired, your eyes get drier.

That’s because basal tear production  is under the control of your hormones, and they follow a daily rhythm,  secreting more tears in the morning and tapering off as the day goes on. Basically, your eyes shift into sleep mode. If you’re experiencing dry eyes  outside of these daily rhythms, blame it on your limbic system.

This part of your brain plays a  big role in behaviors and emotions, but also regulates basal tear secretion, and if you’re sleep-deprived or feeling anxious, you’re producing less of these beneficial tears. Dry eyes don’t feel great  because there’s more friction between your eyeball and your eyelid. Rubbing your eyes actually  triggers a tear-forming reflex.

It stimulates nerves to kickstart  the lacrimal and meibomian glands. The lacrimal gland pumps out tears, while the other produces an  oily film to fight evaporation. And while that all seems fairly logical, rubbing your eyes does  something much stranger too.

It significantly slows your heart rate! In addition to the tear reflex, pressure on the eyeballs also  triggers the oculocardiac reflex. Receptors in the eye and surrounding  tissues sense the pressure and send signals through the  trigeminal and vagus nerves.

Those nerves activate a physical response in  the heart, essentially telling it to chill. Which it does, decreasing your  heart rate by 20% or more! A high heart rate is something we  experience in stressful situations, so slowing your heart rate is thought  by some to have calming effects.

In fact, some forms of massage therapy use this nerve stimulation technique  to try and relax their patients. That said, embracing the urge to bury your fists into your eyes may not be the best idea. This effect is actually known to  cause issues during eye surgeries.

Surgeons have to be careful a  patient’s heart doesn’t slow too much, or even worse stop, because of this reflex. But outside of those rare situations,  other research has shown that chronic eye rubbing causes other problems as well. For example, it might lead to misshapen  corneas that can affect your vision.

So while it might feel good to knead  your fingers into those weary eyes, you’re better off finding relief some other way. Like just going to bed. Thanks to patron Rita Neyer for asking.

If you’ve got a burning question  that you think the SciShow crew might be able to answer, you  can check us out on Patreon. We’ve got an inbox where we  consider questions from our patrons, and sometimes they get made  into episodes like this one. So if you’re interested, you can  learn more at Patreon.com/SciShow. [♪ OUTRO].