It's a hot and humid day, like there's a thick blanket of air sitting on top of Seoul, when I visit the city's bustling Namdaemun market. The place has everything from live eels to military surplus gear, and I go to a corner with rows and rows of electric fans.

Kim Yong Ho has run an electronics shop here for four decades. His grandchildren are running around. And he says he would be very careful about letting them fall asleep in a room with an electric fan sitting next to them on a desk or the floor.

"I would turn the timer on and make sure the winds were blowing very gently," he says. "I'd also make sure the fan head is rotating around the room."

Every culture has its old wives' tales that are unsupported by science. American parents tell their children not to swim after eating, even though there's no real evidence this is dangerous. In South Korea, many older people fear that if you sleep with an electric fan in the room, you may never wake up.

Ah Yun Choi, a 25-year-old shopper, is familiar with this myth.

"I heard that people sometimes die because of the wind, because the temperature goes too low," she says. "But I think that's quite nonsense."

Suddenly her mother Kim Jong Suk, 53, speaks up. You can survive with a fan on all night, she says to her young daughter. But, she adds, for senior citizens it's dangerous.

The South Korean news media and scientists keep trying to debunk this notion, but it won't go away.

A TV ad came out just this summer for a fan called Baby Wind, specifically designed to be safe for children.

"Winds that care about the baby's sleep," the ad says. "As gently as fluttering leaves, free from worries about falling temperature. Automatic off function after two hours, even after mom falls asleep."

Lost In Translation

Do a bit of research on fan death, and you'll find an American climatologist who — at least according to the Internet — says it's a real thing.

That man is Larry Kalkstein of the University of Miami, and he says if you're dehydrated, sitting in front of a fan in a hot room can make you more dehydrated. That can cause medical problems.

But, he's quick to add, "fans do not chop up oxygen molecules in the middle of the night, they can't lead to hypothermia, they can't suck oxygen out of a room. None of those things can happen."

This lost-in-translation moment came a few years ago when Korean journalists interviewed him in Seoul.

"One of the women asked me if I believed in fan death, which I'd not heard of, so I said, 'Yes. Fans can create a problem.'" he recalls.

"But they thought I meant that I believed in traditional fan death, when I did not, so that made a bit of a stir, and that's probably why you're calling me right now, because my name became associated with fan death," he adds.

So for the record, Kalkstein does not believe in fan death.

An Actual Experiment

In 2008, Chun Rim, a professor at the Department of Nuclear and Quantum Engineering at the Korea Advanced Institute of Science and Technology, decided to actually test the hypothesis.

He says it was hard to find anyone to take part in this so-called dangerous experiment. So he used his 11-year-old daughter.

"Every five minutes I checked her body temperature, blood pressure, and also the temperature of her hand," he says.

She survived the night. Her vitals barely changed. And now, the whole family sleeps with fans blowing on them.

"Not necessarily a very strong fan, but we no longer think that this is a real danger," he notes.

That study got some attention when it came out. But seven years later, it doesn't seem to have done much to make this persistent belief blow away.

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