When the air indoors dries out in winter, a humidifier can add much-needed moisture to help relieve the discomfort of a dry nose, throat, lips and/or skin — and even lessen or prevent household problems like static electricity, cracks in furniture and peeling wallpaper.

But how much moisture is too much? Should you choose cool mist or warm mist? And aren’t humidifiers dangerous if you don’t use and clean them right? Here are the facts.

Should you use one at all? Don’t use a humidifier if you or a family member has asthma. And if you or a loved one is allergic to mold or dust mites, be extra-careful about cleaning your humidifier and monitoring indoor humidity levels to make sure they don’t rise too high.

Choose a UL-certified humidifier. Look for the UL logo on the product, says electrical engineer John Drengenberg, consumer safety director for UL. It means samples of the product have been tested for compliance with important safety standards.

Put it in the right spot. “You don’t want adults or children to bump into it or trip on the power cord,” explains Drengenberg. “Find a spot where young children can’t reach it, too. A child who sees you filling the humidifier might try to open it up.” Experts recommend:

  • Put your humidifier on a flat waterproof surface about three feet off the ground.
  • Make sure the power cord is out of the way, so no one will step or trip on it. Keep the cord away from heated surfaces like radiators, too.
  • In a baby or child’s room: Keep the unit out of reach so your young one can’t climb on it or play with it.
  • Point the mist away from electrical outlets. Over time, water build-up could make an outlet rust or even cause a short circuit, Drengenberg notes.

Fill your humidifier with this, not that. Use cold water. “Hot water contains more minerals, which can create scale inside the humidifier,” says Drengenberg. “Those mineral deposits become a breeding ground for bacteria and mold.” Distilled or demineralized water can help cut that risk — and may also cut risk for “white dust,” humidifier vapor filled with minerals from the water. While the Environmental Protection Agency says white dust is not a serious health hazard, University of Utah researchers found evidence of lung problems in a young child who was exposed to it. Demineralization cartridges or filters are another good way to reduce risk for white dust. Use one if the owner’s manual recommends it.

Never add medicine, oils, perfumes or bath salts to the humidifier’s water tank.

Keep it clean. The Consumer Product Safety Commission warns that mist laden with bacteria, mold and mildew from a dirty humidifier can trigger lung problems, causing flu-like symptoms or even a lung infection. Follow these steps to keep your unit clean:

  • Empty and refill the tank daily. Always unplug the device first.
  • Clean the unit as recommended by the manufacturer. If there are no cleaning instructions, the EPA suggests cleaning your humidifier as often as every three days. After you unplug it and empty the tank, use a brush to clean the inner walls. Remove mineral deposits and film from all interior surfaces you can reach. Wipe dry. Use cleaning products recommended by the manufacturer or a 3 percent hydrogen peroxide solution on all parts that touch water. Rinse several times. Clean or replace filters and belts as needed, too.
  • Empty and dry the tank (and unplug the unit) when not in use. Drain and clean your humidifier before putting it away for the season. Clean it again before you use it next time.

Don’t over-moisten the air. Ideal indoor humidity is 30 to 40 percent. When levels creep higher, moisture settles on surfaces, creating a haven for bacteria, mold and dust mites. Monitor humidity with an inexpensive device called a hygrometer, available at hardware stores. Or just be careful not to run your humidifier for so long that walls and windows feel or look wet, says Drengenberg.

While running your humidifier, leave the door to the room open partway to encourage air flow and help avoid too-high humidity levels. Point the mist upward and away from walls and corners. Then enjoy breathing in the nice, dewy air!

Sari Harrar is an award-winning health, medicine and science journalist whose work appears in Dr. Oz The Good Life magazine, Good Housekeeping, O--Oprah Magazine, Organic Gardening and other publications.