Humidifiers that make antibacterial claims might seem like the perfect solution for consumers who use these small appliances but dislike cleaning them. And according to an informal survey, that’s most people: 59 percent of respondents who use a humidifier told us they do not clean it every day and one in four people clean theirs twice a month or less.

That could be a mistake. 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 recent safety study, Consumer Reports found that, when it comes to preventing bacteria from being released into the air, antimicrobial features are no substitute for regular cleaning.

Antimicrobial claims are found on more than half of the humidifiers in our tests. Humidifiers that claim to be "germ-free" or produce "clean mist" use technologies such as UV light and "patented" ionic silver that are supposed to keep the water clean.

We took the 34 humidifiers that had already been tested in our labs for performance and ran two additional tests: One to see whether bacteria would grow in the water reservoirs, and another to see whether bacteria added to reservoirs could then be emitted into the air.

We based our study on three days of continuous use. After that time we measured microbial growth in the reservoir and found that most of the humidifiers contained increased microbial growth compared to levels found in tap water. The next step was to determine whether the bacteria was emitted into the air, so we added bacteria to the reservoirs of new samples and noted whether it was released into the air.

Of the three types of humidifiers we tested—evaporative, ultrasonic, and vaporizer—we found that none of the evaporative models emitted airborne bacteria. All but one model of the other two types, a vaporizer, emitted bacteria

The two humidifiers we tested that are worth mentioning for having both a minimal amount of bacteria growth and for not emitting bacteria into the air are the Honeywell HCM-350 evaporative humidifier and the Vicks V150SGN vaporizer.

The Honeywell HCM-350 evaporative humidifier.
The Honeywell HCM-350 evaporative humidifier.

How Humidifiers Work

In the heating season, the humidity in your home can drop to 10 percent while a level between 30 and 50 percent is recommended. Less than that can lead to sore throats and dry skin while 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 and are not recommended for use around children.

Keep It Clean

Don’t depend on a certain model or antimicrobial claims to protect you from bacteria buildup. The bottom line is that when you use a humidifier, you need to clean it every day. 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

Bottom line. If you’re concerned about bacteria emissions, consider an evaporative humidifier or the Vicks V150SGN vaporizer. But whatever type you choose, make cleaning part of your routine. Here are the 10 evaporative humidifiers that did not emit bacteria in our tests, listed in order of performance. In addition, there was no bacterial growth in the tank of the Honeywell HCM-350 evaporative model or the Vicks V150SGN vaporizer.

For more choices see our full humidifier Ratings and recommendations.