Mind & Body

Why Do You Open Your Mouth When Applying Mascara?

That face you make when inserting contacts, putting on eyeliner, or applying mascara is a bizarre human quirk right up there with sneezing in sunlight and contagious yawning. Why do you feel a compulsion to open your mouth when it comes to messing with your eyes? There's no definitive answer, but the leading theory is pretty compelling.

Open Wide!

To understand so-called "mascara mouth," you need to understand a few things about the anatomy of your head. The muscle mainly responsible for opening and closing your mouth is called the lateral pterygoid, and that's controlled by the central sensation highway known as the trigeminal nerve. The muscle that lifts and lowers your upper eyelids, on the other hand, has the Harry Potter-esque name of levator superioris, and that's controlled by the oculomotor nerve.

The trigeminal nerve and the oculomotor nerve originate really close together in the brainstem. The leading theory behind mascara mouth is that, to put it simply, those wires can get crossed. When you activate the oculomotor nerve to keep your eyes open to avoid making a mess of mascara or contacts, you end up activating the trigeminal nerve and opening your jaw. Bam, mascara mouth.

Blink and You'll Miss It

There are other theories as well: Some say that opening your mouth simply stretches your facial skin to make a sturdier surface for makeup. That could be true as well. But there's one scientific phenomenon that lends some credence to the nerve theory: In some children, a condition called Marcus Gunn Jaw-winking syndrome makes them wink one or both eyelids every time they move their jaw. Mascara mouth is no syndrome, but it could be a mild version of this neurological fluke.

Get stories like this one in your inbox or your headphones: sign up for our daily email and subscribe to the Curiosity Daily podcast

Hear how long we've been adorning our faces in the New York Times bestselling book "Face Paint: The Story of Makeup" by Lisa Eldridge. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer October 23, 2017

Curiosity uses cookies to improve site performance, for analytics and for advertising. By continuing to use our site, you accept our use of cookies, our Privacy Policy and Terms of Use.