There's a good chance you're just not cleaning it properly.

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There are a lot of reasons to love your humidifier, especially during the cold, dry winter months. By releasing more moisture-filled air into your home, these handy gadgets could help you fight the flu, ease dry eye, and combat dry skin and sinuses. Thing is, there's a chance you're not cleaning yours properly—and you could be setting yourself up to get seriously sick.

Studies have shown that as many as 75% of swab samples from humidifiers reveal fungal growth, while as many as 87% reveal bacteria growth, says Aileen M. Marty, MD, an infectious diseases professor at Florida International University. "This happens not only in homes, but also in clinics and hospitals—including ICUs," she says.

Breathing contaminated air from a dirty humidifier puts you at increased risk for developing pneumonia, asthma attacks, or lung conditions such as Legionnaire's disease. And if you have a chronic breathing condition, a humidifier can actually aggravate symptoms: "Although increased humidity can ease breathing in children and adults who have asthma or allergies, ironically, when the humidifier is releasing dirty mist—mist that may include an increased growth of fungi that act as allergens—”they can trigger or worsen asthma and allergy symptoms," Dr. Marty says.

Here, four important ways to use your humidifier safely.

Change the water often

"Bacteria and fungi thrive in standing water left inside of a humidifier—and a whole lot of them will accumulate in only a couple of days," Dr. Marty warns. For this reason, you should ideally change the water in your humidifier every day to prevent bacteria and fungus from taking over, especially if you use a "cool mist" or ultrasonic humidifier. Humidifier filters should be replaced every two months.

Not all cleaning methods are created equal

Simple cleaning solutions are best here. Dr. Marty recommends using water or an alcohol-based cleaner to refresh your humidifier, being sure to unplug the unit before emptying the water tank, then drying the inside surfaces and refilling with clean water. If there are any mineral deposits or film on the top of the tank, remove them using an ethanol-based cleaner, such as Purell Cottony Soft Sanitizing Wipes ($30 for six cannisters;

"You should never use chemical cleaners, such as products that contain hydrogen peroxide," she says. The reason? "There is a horrible condition that can develop if someone uses the wrong type of humidifier disinfectant called 'humidifier disinfectant-associated lung injury.' It's characterized by spontaneous air leak in their lungs, rapid progression, lack of response to treatment, and can even be fatal."

Use the right water

Sorry, but tap won't cut it. "You should always fill your humidifier with bottled, pre-filtered, or demineralized water," says Dr. Marty. Demineralized cartridges or filters are also helpful to use if compatible with your unit, he adds. And although you might be tempted to think that using filtered water will let you skip a cleaning or two, that's not the case: "Even when you use filtered water, you still have to clean and store your humidifier properly every day," she says.

Replace it

"Over time, humidifiers eventually build up deposits that are difficult or impossible to remove and encourage growth of bacteria and fungi," Dr. Marty says. In other words, if your unit is more than a few years old or if you haven't been cleaning it regularly, it's better to err on the safe side and invest in a new one. The good news? Many humidifiers are affordable: Here are our editor-approved picks.

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