For those of us whose skin in the winter gets as scaly as a lizard’s, home humidifiers might sound essential. But humidifiers are more complicated to use and care for than some other household appliances—and doing so incorrectly can be worse for your health than not having one at all.
Here’s what to know before diving in.
The benefits of humid air
Humidifiers do their best work on the parts of the body you use to breathe. When the air gets colder, the humidity in the environment goes down. Each breath of dry air sucks moisture from your airways, which can leave your nose and throat parched and more prone to irritation. Dryness can lead to issues like nosebleeds, persistent coughs, and discomfort, especially for people with lung diseases like asthma and COPD.
“Having a humidifier, particularly if you have asthma, can decrease those symptoms and make you feel more comfortable,” says Dr. Kyle Enfield, a pulmonary expert and an associate professor at the University of Virginia’s School of Medicine. “When you have a cold, they can make you feel less congested.” The extra environmental moisture from a humidifier can also help ease allergies and improve your quality of sleep by allowing for easier breathing.
Some humidifiers are designed to respond to moisture levels in the air, but others may continue pumping out mist until they’re turned off. Which kind you use will inform how long you should let it run for, though moisture levels tend to be pretty easy to sense (and you can measure them with a humidity monitor). “People are going to feel most comfortable with the humidity in their home at about 30-50%,” Enfield says.” You get much higher than that, and it’s going to start feeling stuffy and uncomfortable. You get much lower than that, and you’re going to start feeling dry eyes and a dry nose.”
What type of humidifier is best?
If you’re looking for a machine for a single room or a small apartment, two types are available: ultrasonic and evaporative. Ultrasonic humidifiers are more common and operate via an internal element that vibrates at a high frequency, generating a mist of water droplets that a small fan pushes up into the air. If you’ve ever seen a humidifier with a dense, fog-like plume spurting from it, it’s probably ultrasonic.
Evaporative humidifiers use a sponge-like wicking filter which sits partially submerged in water. A fan inside the machine pushes air through the filter and back out the top, creating a cool mist that carries evaporated water into the air.
Each type has strengths and weaknesses, both in terms of health and in terms of noise, humidity control, ease of care, and cost. Evaporative humidifiers, for instance, are less likely to make your air feel muggy and may be safer for tap-water users, while ultrasonic humidifiers are often quieter and require less expensive replacement filters. Experts say that there’s no one right answer—it’s more important that you care properly for whatever you buy by replacing filters and cleaning as recommended by the manufacturer.
What kind of water should you use in a humidifier?
Once you’ve picked a humidifier, you have to choose what goes in it. “The best option is always distilled water,” says Andrea Dietrich, a professor of civil and environmental engineering at Virginia Tech. Many manufacturers also recommend using distilled water, which is the only way to ensure that the mist being pumped out contains only H2O molecules. For most people, though, sticking to distilled water is pretty impractical: it takes a long time to make on a stovetop, and stocking up on enough distilled water to routinely fill a humidifier can get costly, heavy, and wasteful.
So what’s wrong with using tap water? Tap water and bottled drinking water are full of minerals like zinc, calcium, and magnesium, and in any humidifier that doesn’t boil water (a feature included mainly in industrial units), they get shaken or blown right into the air alongside water molecules. Metals and other minerals are great for you in drinking water, because they help the body stay hydrated, “but there’s a difference in toxicology between ingestion and inhalation,” Dietrich says. “Those particles, especially from ultrasonic humidifiers, are really small.” At less than one micron, they’re able to travel far inside the respiratory system when inhaled, and can get stuck deep in the lungs where the exchange of oxygen and carbon dioxide occurs. Though certain metals can be more damaging than others in this context—there’s some evidence, for instance, that inhaling manganese can harm the brain— the particle size is most important. If the buildup gets dense enough, it can interfere with the gas exchange in the lungs and make it harder to breathe.
This type of serious lung injury from using a humidifier with tap water is very rare and has mostly been documented in children, whose smaller lungs can be overwhelmed quicker, says Dietrich, but scientists still aren’t sure if lower levels of mineral buildup pose risks to healthy adults as well. Some amount of buildup “might slowly dissolve over time, but your lungs really aren’t designed to dissolve things,” she adds.
A small amount of evidence suggests that evaporative humidifiers may release fewer minerals from tap water into the air than ultrasonic humidifiers do. Dietrich also recommends looking up your local water source and finding the number of total dissolved solids, a U.S. Environmental Protection Agency-mandated measurement that quantifies your tap water’s overall mineral content. There’s no clear cutoff number she recommends for safety, but finding out if your water is on the higher end or lower end can help inform your decision. And don’t bother with the Brita for your humidifier’s water, Dietrich adds. “They will take out the big minerals like calcium, magnesium, lead, and copper, if you have them, but they put in sodium potassium, so you still have a lot of total dissolved solids. All it does is exchange minerals.”
The bottom line? While tap water in a humidifier probably won’t hurt you, only use distilled water in a baby’s room, says Dietrich.
How to clean a humidifier
The inside of a neglected humidifier—damp, dark, and warm—is the perfect environment for mold and bacterial growth. Those bacteria can get blown right back out of the machine with the water, creating a funk-filled mist full of microorganisms and headed right for your nostrils. Natalie Hull, a clinical assistant professor in civil engineering at Boise State University, who has studied the output of humidifiers, says that these clouds can contain “fungi, spores, or endotoxins—parts of bacteria that might irritate your respiratory system even though they’re not whole living cells.” That’s not necessarily as gross as it sounds; most people’s immune systems are used to interacting with microbes like this routinely. But the U.S. Consumer Product Safety Commission warns that these organisms can pose more serious threats to people with allergies or asthma. Hull has also found that more robust microbial communities grew in humidifiers that use tap water compared to distilled, since they feast on the minerals it contains.
Microorganism growth can easily be prevented by cleaning your humidifier thoroughly and regularly wherever water touches it. Experts recommend cleaning it every 2-3 days while it’s in use, as well as before packing it away if you’re taking a break from using it. Any simple disinfectant will work, as will a vinegar solution, but before drying your humidifier, be sure to “rinse it copiously with tap water” says Dietrich. Like fungal and bacterial growths, any cleaning product left behind will be blown back out into the air, where it can irritate your airways. Pay special attention to scales, crusty bits, or slimy areas of the machine—these textures all indicate the growth of potentially airway-irritating microorganisms.