NEW YORK (WABC) -- You expect a humidifier to add moisture to the air, but if you don't clean it often enough, it could be adding more than that.
A dirty humidifier can emit bacteria into the air, and that could be a problem for people with asthma or allergies.
Many manufacturers make antibacterial claims like "produces pure bacteria-free vapors" or "germ-free mist" and "antimicrobial material."
Consumer Reports tested 34 humidifiers in three categories: Vaporizers that emit steam, ultrasonic humidifiers that release a fine mist, and evaporative humidifiers that blow air over a wet wick filter.
Over the course of three days, testers measured the microbial growth in the humidifiers' tanks.
In a second test, they added bacteria to each tank and measured whether any bacteria came out in the humidifier's mist.
"Humidifiers with antimicrobial claims weren't necessarily any better at preventing bacterial growth or emitted bacteria," Consumer Reports Dory Sullivan said.
What did make a difference in Consumer Reports' tests was the type of humidifier.
All of the ultrasonic humidifiers and all but one of the vaporizers emitted some bacteria, but none of the 10 evaporative wick models emitted any bacteria.
With any type of humidifier, the safest approach is to empty, rinse, and dry it out every day. And once a week, follow the manufacturer's instructions on how to disinfect the tank.
Consumer Reports says if you have an infant or suffer from asthma or allergies, consider the Vicks Warm Mist Vaporizer for $15. Or, for larger rooms, consider the Honeywell evaporative humidifier for $60.
Neither grew or emitted bacteria in Consumer Reports tests.
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