Here's The Real Reason You Yawn

Most of us will attempt to stifle a yawn if we're in a professional setting or listening to someone especially intimidating giving a speech since it's generally considered impolite. But our watery eyes tend to give us away no matter how well we hide the yawn. Funnily enough, the reason this happens is that you generally screw up your face while yawning, which pushes the tears out, rather than it being an involuntary physical response.

"[The] tightening of the facial muscles around the eyes when we yawn causes the pool of tears that normally coat our eyes (i.e. our tear film) to 'overflow,'" Dagny Zhu, MD, an eye surgeon with Nvision Eye Centers, explained to Well + Good. "Facial muscles also put pressure on the lacrimal gland, which 'squeezes' out tears." Weirdly, our eyes tearing up is a part of the cooling-off process too, similar to when we sweat during exertion to keep our bodies from overheating. 

If your eyes don't tear up when you yawn, it could be because of an underlying autoimmune disease, which affects tear production. On the other hand, seasonal allergies, contact lenses, and certain makeup products can all cause the eyes to water more.