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Kevin C. Cox/Getty Images
Kevin C. Cox/Getty Images

How Effective is the Eye Black that Athletes Wear?

Kevin C. Cox/Getty Images
Kevin C. Cox/Getty Images

Sometimes it’s literally a glob of grease, other times it’s a synthetic sticker. We’ve all seen baseball and football players with the black rectangles under their eyes on sunny days, which is thought to help reduce the sun’s glare and allow athletes to better pick up the ball. But does it actually work?  

The underlying concept behind eye black is that it reduces the amount of glare that reaches your eyes thanks to the fact that the color black absorbs most light frequencies. In theory, excessive light from sources in our peripheral vision will be absorbed by the black color, increasing the contrast of the objects we're are looking at and focusing on directly.  

There have been a handful of studies done in the past decade, including one by the University of New Hampshire and one by Yale University. Although these two and others began with skepticism and have all yielded slightly different results—while accounting for the effect of variables such as eye color and gender—they have agreed that traditional eye grease made of beeswax, paraffin, and carbon does in fact reduce glare and improve contrast sensitivity. They also all concluded that anti-glare stickers and petroleum jelly have no impact.

“I thought we would find it to be like war paint and a psychological advantage more than anything else,” Dr. Brian M. DeBroff, the lead author of the Yale study, told The New York Times. “We were surprised to find a benefit from the grease.”

Even though the effect was found to be somewhat minimal, DeBroff has adopted somewhat of an “it can’t hurt” stance regarding its application to high-intensity sport situations.

“Certainly in football and baseball, where tracking a ball at high speed is an important aspect, any competitive advantage could be beneficial,” DeBroff said.

Despite this, researchers are still unsure how much impact the glare reduction and contrast improvement translates into an “on-the-field” advantage for athletes. Dr. Kenneth Fuld, chairman of the University of New Hampshire’s psychology department and the sponsor of the aforementioned study conducted by the university, points out that tennis players regularly perform at a high level despite the fact that they do not wear eye black.

“I would be highly doubtful that it would have much of an effect, if any,” Fuld said.

Although it is extremely reasonable to conclude that it is a coincidence, it is interesting to note that last year’s two top NFL receivers in terms of receiving yards, Calvin Johnson of the Detroit Lions and Andre Johnson of the Houston Texans, both regularly wear eye black during games.

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Big Questions
Why Is the American Flag Displayed Backwards on Military Uniforms?
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In 1968, famed activist Abbie Hoffman decided to crash a meeting of the House Un-American Activities Committee in Washington by showing up in a shirt depicting the American flag. Hoffman was quickly surrounded by police, who ripped his shirt off and arrested him for desecration of the Red, White, and Blue.

Hoffman’s arrest is notable today because, while it might be unpatriotic to some, wearing the American flag, burning it, or otherwise disrespecting it is not a violation of any federal law. In 1989, the Supreme Court ruled that it would be unconstitutional to prosecute any such action. Still, Americans have very fervent and strict attitudes toward displaying the flag, a longstanding symbol of our country’s freedom. According to the U.S. Flag Code, which was first published in 1923, you shouldn’t let the flag touch the ground or hang it upside-down. While there’s no express prohibition about reversing the image, it’s probably a safe bet you shouldn’t do that, either.

Yet branches of the U.S. military are often spotted with a seeming mirror reflection of the flag on their right shoulder. If you look at a member in profile, the canton—the rectangle with the stars—is on the right. Isn’t that backwards? Shouldn’t it look like the flag on the left shoulder?

The American flag appears on a military uniform
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Not really. The flag is actually facing forward, and it’s not an optical illusion.

When a service member marches or walks forward, they assume the position of a flagpole, with the flag sewn on their uniform meant to resemble a flag flapping in the breeze. With the canton on the right, the flag would be fluttering behind them. If it were depicted with the canton on the left, the flag would be flying backward—as though it had been hung by the stripes instead of the stars nearest to the pole. The position of the flag is noted in Army Regulation 670-1, mandating the star field should face forward. The official term for this depiction is “reverse side flag.”

As for Hoffman: His conviction was overturned on appeal. In 1970, while at a flag-themed art show in New York, he was invited to get up and speak. He wore a flag shirt for the occasion.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
What Causes Sinkholes?
Mark Ralston/AFP/Getty Images
Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

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