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Why Does Hair on Moles Grow More Quickly?

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In medieval Europe and early colonial America, moles were seen as a sign of demonic possession (as was everything else). The ancient Greeks and Chinese, however, used the markings to try to decipher personality traits or destinies. In the age of modern pop culture, icons like Marilyn Monroe, Goldie Hawn, Cindy Crawford, and Madonna have turned moles into beauty marks to be desired and even emulated. But as anyone whose skin is accentuated by a mole can tell you, there is something particularly unique about them: They seem to grow hair at a faster rate than ordinary skin, and that hair often seems darker and coarser.

Why is this? Why do hairs burst forth from moles more quickly than they do from ordinary skin? Science actually doesn’t know.

“The short answer is that we’re not sure why the hair is coarser in moles or why it may seem to grow faster,” Lauren Ploch, a dermatologist based in Augusta, Georgia, tells mental_floss. “The development of moles is still a dermatologic mystery, as is the regulation of hair growth.”

When viewed under a microscope, nevus cells, a kind of melanocyte found in moles, don't invade the structure of hair follicles and seem to have no effect that would change hair appearance or growth, says Ploch.

Researchers do know that mole skin is different from other skin and develops as the result of a number of factors, including genetics, environment, hormones, and signaling proteins. Many of these elements (especially hormones and signaling proteins) also contribute to hair growth, says Ploch. So the presence of the mole and the underlining causes of it may tinker with the usual bodily factors regulating hair growth.

“I suspect that, while the mole itself may not have a direct role in creating a darker, coarser hair, the local milieu of signaling molecules and hormones in the skin that created the mole leads to a darker, coarser hair within the lesion,” she says.

She adds that moles often develop during puberty in response to androgen, the same steroid hormone that spurs facial and pubic hair growth, so moles and hair have a common stimulus. 

Science has yet to fully explain the behavior of moles, but at least we know more about them than we did during the middle ages.

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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?
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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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