When Consumer Reports asked consumers how often they clean their humidifiers, 59 percent of respondents who use one told us they don't clean it every day—and one in four people said they clean it twice a month or less. That's a mistake.

More on Humidifiers

Both the federal Consumer Product Safety Commission and the Environmental Protection Agency warn that emissions from dirty humidifiers can cause health problems, especially for folks who suffer from asthma or allergies. And in a past safety study, we found that microbes can grow in the reservoirs of humidifiers and that bacteria can be released into the air in the mist.

We tested three types of humidifiers and found that the evaporative ones were the least likely to emit airborne bacteria. But don’t depend on the type to protect you from bacteria buildup.

“Bacteria can only grow in a moist environment, so it’s important to wash out the base tray and reservoir and let it completely dry,” says Doris Sullivan, CR's associate director for product safety.

How Humidifiers Work

In the heating season, the humidity in your home can drop to 10 percent; a level between 30 and 50 percent is recommended. Humidity levels lower than that can lead to sore throats and dry skin. On the other hand, too much moisture can encourage the growth of mold and dust mites. Here are the types of humidifiers to consider:

  • Ultrasonic humidifiers use a vibrating nebulizer and emit a cool mist.
  • Evaporative tabletops blow unheated air over a wet wick.
  • Vaporizer models use a heating unit to boil the water and emit steam. They're not recommended for use around children.

How to Clean Your Humidifier

The bottom line? When you use a humidifier, you need to clean it every day no matter what type it is. Not all manufacturers make that recommendation, but we do. Here’s a good routine to follow:

  • Every day. Empty, rinse, and dry the base tray or reservoir before refilling.
  • Every week. Remove water scaling with vinegar, and disinfect the unit with a bleach solution following the manufacturer's instructions.
  • Before storing. Clean to remove scaling, disinfect with a bleach solution, and dry thoroughly.
  • After storing. Before using again, clean to remove scaling, disinfect with a bleach solution, and dry thoroughly. Don’t fill it before you need to.

Humidifiers to Choose

If you’re concerned about bacteria emissions, consider an evaporative humidifier. Some examples from our humidifier tests include:

And although it’s a vaporizer, the Vicks V150SGN, $25, also did well in our tests and didn't emit bacteria.