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People should be especially cautious with ultrasonic or "cool mist" humidifiers. On the market since the late 1980s, these types are popular because they're cheap, quiet and energy efficient. They work by basically pulverizing water into a fine mist with high-frequency vibration. The problem, says Dr. Deterding, is that they turn everything that's in the water into mist, too.
"Bacteria, chemicals, minerals, mold — they aerosolize all that stuff to the right particulate size that you breathe it right into your lungs, and it can be toxic," says Dr. Deterding. "One of our patients developed chronic lung disease symptoms. We eventually figured out it was the humidifier."
That's because water from the tap, and even bottled water, has minerals in it — basically rock dust. That's not a problem when it's suspended in water. When it's floating around in the air, it is. The telltale sign for that is the "white dust" that settles around the room.
Minerals aren't the only problem. Any bacteria or mold in the humidifier gets shot right into the air, too — and Consumer Reports found that humidifier models claiming to be anti-bacterial aren't particularly effective.
And if parents use chemicals to clean the humidifier, those chemicals go right into the lungs, too, sometimes to disastrous effect. In South Korea, dozens of children were sickened or died from breathing a humidifier disinfectant that turned out to be toxic.
Almost needless to say, the popular practice of dropping a little essential oil or vapor rub in these humidifiers is also not good.
"It's a cost-benefit scenario," says Dr. Deterding. "Humidifiers are fine for what they do, but you have to be willing to maintain them, to hold onto that manual and follow all the cleaning instructions and the fine print — or they're harmful. And I think for most parents, myself included, you can't maintain it like you should, because life just gets in the way."
That's why, for Dr. Deterding's money, she prefers saline nasal drops for dry throats and nasal passages. "They're just as effective, and they're safer," she says.
So there's hope, even for parents who already own an ultrasonic humidifier and are feeling understandably reluctant to throw it out — as long as they're willing to put in the work. Another option: switch to an evaporative humidifier, which will emit neither minerals nor bacteria, although the filter will need frequent changing.
Whatever you decide to use, clean it often — without chemicals. "Just regular old dish soap," Dr. Deterding says, "will do nicely."
No matter what type of humidifier you have, here's how to use it safely:
The oldest and most basic type of humidifier, these create steam by boiling water.
These run room-temperature water through a wet wick to evaporate it into the air.
These humidifiers turn water into a fine mist via high-frequency vibration.