Determine Your Ideal Eyelash Length With Science

How the “one-third rule” protects your eyes

Beau Lark/Corbis

We use them to bat, wink, flirt and flick away tears. But what’s the real purpose of eyelashes? That’s long been subject to debate—and new research suggests not only an explanation but a way to measure the ideal eyelash length.

After an odyssey involving museums, wind tunnels and a makeshift eye, a team of researchers has discovered what they think is the true purpose of the lash: controlling airflow around the eye. The New York Times reports that lead scientist David Hu became intrigued by eyelashes after gazing into his newborn baby’s eyes. He enlisted his colleagues at Georgia Tech to measure the lashes of 22 species of mammals, from giraffes all the way down to hedgehogs.

In their hunt for the true meaning of eyelashes, the team went to the American Museum of National History to inspect preserved animals and built a two-foot wind tunnel with a simulated eye. They found that mammals tend to have lashes that are a third as long as the width of the eye—and when they put their fake eye to the test in the wind tunnel, they figured out that the “one third rule’ leads an ideal eye environment.

“As short lashes grew longer, they reduced air flow, creating a layer of slow-moving air above the cornea,” said Hu in a release. “This kept the eye moist for a longer time and kept particles away. The majority of air essentially hit the eyelashes and rolled away from the eye.” But the opposite was true with longer lashes, which created a cylindrical effect that diverted airflow toward the eye and caused quicker evaporation.

So what does that mean for long lash lovers who buy fake lashes and even experiment with Oreo cookie mascara in pursuit of flirty fringe? Though the study suggests that longer lashes aren’t exactly ideal, the team concedes that fake lashes could serve a purpose anyway:

“Even if they're not the correct length, more eyelashes are always better than less,” said Alexander Alexeev, an associate professor in the School of Mechanical Engineering. “If fake eyelashes are dense enough, they may give the same overall effect in protecting the eye even if they are longer than one-third.”

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