Children's Hospital Colorado
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Just Ask Children's

The Hidden Danger of Humidifiers

A white humidifier has a smokey vapor coming out of it while a young girl reads a blue book on a red bed with white pillows in the background.

When the furnace is on in the winter, humidity levels in the home can drop by 10%. More aridity can lead to sore throats, chafed nasal passages and dry skin, especially for little ones.

“It’s common in Colorado to use humidifiers,” says Dr. Robin Deterding, medical director of our Breathing Institute. “But people should use them cautiously.”

Are ultrasonic humidifiers safe?

That goes especially for 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.

It’s more than just minerals

Minerals, though, aren’t the only problem. Any bacteria or mold in the humidifier gets shot right into the air, too — and Consumer Reports found that 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.

So what’s a parent to do? Dr. Deterding recommends cutting out the humidifier entirely. “For dry throats and nasal passages, saline nasal drops are far better than humidifiers. They’re just as effective, and they’re safer,” she says.

But hope for the humidifier faithful is not lost, even for parents who already own an ultrasonic humidifier and are feeling understandably reluctant to throw it out. There’s a way to use them safely — with caution. 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.”

 Dr. Deterding, wearing a white doctor coat and stethoscope, looks inside a young boy's mouth.

Humidifier 411


The oldest and most basic type of humidifier, these create steam by boiling water.

  • Advantages: because these heat water to boiling, the vapor they release is very hygienic.
  • Disadvantages: They get hot and can burn, especially left in children’s rooms unattended, such as overnight.


These run room-temperature water through a wet wick to evaporate it into the air.

  • Advantages: Also inexpensive, these are both cool and hygienic. A recent Consumer Reports study found that this type emits neither bacteria nor minerals.
  • Disadvantages: Filters quickly get dirty and need frequent changing.


These humidifiers turn water into a fine mist via high-frequency vibration.

  • Advantages: They’re cheap, quiet and energy efficient, and they won’t burn.
  • Disadvantages: They aerosolize not just water, but everything in it, such as bacteria and minerals.

How to use an ultrasonic humidifier safely

  • Use only distilled water (which contains no minerals)
  • Clean frequently with soap and water — no chemicals
  • Never add essential oils or vapor rubs
  • Never use in an enclosed space — leave bedroom doors open
  • Keep an eye out for white dust, and if you see any, stop using immediately

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