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The Rumor: Humidifiers should be cleaned every once in a while

If you've ever lived in a dry climate, chances are you’ve had a humidifier in your house at some point. Legend has it they need to be cleaned from time to time. Really cleaned, as in a proper, follow-all-of-the-instructions type of cleaning. And that makes sense. It really does. After all, a humidifier is a device that holds water and vaporizes it into the air, and you end up breathing that vapor. You wouldn’t drink coffee from a coffee machine containing month-old water, would you? But just how often -- and how well -- do humidifiers need to be cleaned, anyway? Does anyone know for sure?

The Verdict: Clean your humidifier regularly -- and thoroughly

First things first, ladies and gents. Dig out your humidifier owner’s manual -- check in the bottom drawer you haven’t looked in since 2007 -- and flip to the page marked “cleaning your humidifier.” Chances are, the manufacturer will recommend that you clean your humidifier with either vinegar or bleach. Bleach.

Why bleach, you ask? "There are definitely health issues that can crop up from using a humidifier that has developed mold or mildew or bacterial contamination," says board-certified dermatologist Jessica Krant, MD, MPH, assistant clinical professor of dermatology at SUNY Downstate Medical Center in NYC. "Itchy skin rashes and itchy eyes could be a sign of mold or mildew allergy coming from the humidifier." The bleach will kill that unhealthy mold and mildew.

Fair enough. But the real question is how often you need to clean that humidifier (because, let's face it, it's a pain in the ass). After a fair amount of research, we found that humidifier manufacturers offer a range of advice, from cleaning it after the season and before storage to cleaning it several times throughout the dry winter season.

The common thread? It's advised that you clean your humidifier after you’ve used it for a couple of months, after heavy daily use, or after you’ve pulled it out of the closet without cleaning it for several weeks.

"Just follow the directions," says Cliff Bassett, MD, medical director of Allergy and Asthma Care of New York and associate professor of clinical medicine at New York University. "You don’t want it sitting around for weeks with water, as you can get mold."

According to Bassett, you don't want to overdo it with the humidity. He recommends using a hygrometer to measure the amount of moisture in the air. "You don’t want it to be greater than 45 percent," he says.

Bassett also stresses that humidifiers are not good for allergies. The problem from an allergy point of view is that as you increase humidity indoors, you’re giving nourishment to dust mites and molds -- and a lot of people are allergic to those two things.

The moral of the story? Clean your humidifier! Dig out your manual (go to the manufacturer's website if you’ve lost it), follow the instructions, then breathe in the glory of your newly cleaned and healthy-to-use humidifier.