Mold in Humidifier: How to Clean It and Stay Healthy

A humidifier is a container of water sitting at room temperature, often for days. The EPA puts it plainly: microorganisms often grow in humidifiers which are equipped with tanks containing standing water. The CDC lists humidifiers among home devices where germs can grow and says to empty and clean tanks on humidifiers daily.

The other problem is the humidity itself. Too much moisture in a room feeds mold on walls, windows and furniture. The EPA says do not humidify to indoor relative humidity levels exceeding 50 percent and do not permit the area around the humidifier to become damp or wet.

Do Texans even need one?

It depends where you live. Texas precipitation ranges from less than 10 inches in the far west to more than 60 inches in the extreme southeast. In El Paso or Lubbock, a humidifier can make a dry winter more comfortable. In Houston, Beaumont or Corpus Christi, the Gulf is the primary source of moisture and the house more often needs a dehumidifier, not a humidifier. A cheap hygrometer tells you which side of 50 percent you're on.

Not all humidifiers handle dirty water the same way. Here's how the EPA describes them:

Table: Humidifier types and mold spread, per EPA.

The EPA says ultrasonic and impeller units can disperse materials, such as microorganisms and minerals, from their water tanks into indoor air. Evaporative and steam types still grow microorganisms in standing water, but generally disperse less, if any, of these pollutants into the air.

Steam units have their own risk. The EPA says to keep steam vaporizer humidifiers out of the reach of children, because steam and boiling water may cause burns.

What to look for when buying

• Easy to clean. A wide tank opening you can get a hand or brush into, and few hidden crevices.
• Parts that come apart. If you can't reach the base, you can't clean it.
• Clear maintenance instructions. The EPA says to follow the manufacturer's instructions regarding the use, maintenance, and replacement of any materials supplied with the humidifier, such as wicks, filters and demineralization cartridges.
• A built-in humidistat, so it shuts off before the room gets too damp.

We don't rate or recommend specific brands.

These steps follow the EPA's guidance for portable units. If your manual gives different instructions, follow the manual.

1. Unplug it. The EPA says to unplug the unit from the electrical socket first before emptying or cleaning.
2. Empty and take it apart. Remove the tank, cap, any wick or filter, and the base reservoir.
3. Scrub off visible growth. Use a soft brush and warm water on the tank walls, cap threads and base. Pink or black film counts.
4. Disinfect. Where the maker gives no specific guidance, the EPA recommends a 3% solution of hydrogen peroxide, then rinsing the tank thoroughly. Some manuals call for diluted bleach or vinegar instead; use what yours says. If you do use bleach, the CDC says never mix bleach with ammonia or other cleaners.
5. Rinse well so no cleaner gets misted into the room.
6. Replace or clean the wick or filter as your manual directs.
7. Dry everything. The CDC says to let them air dry after cleaning.

Mold on humidifier surfaces and around it

Mold on the humidifier's outside, or on the wall, window or furniture next to it, is a sign the room is too humid. Move the unit away from walls, lower the setting, and clean the surface. The EPA says to scrub mold off hard surfaces with detergent and water, and dry completely. If it's on drywall, see mold on walls, and for windows see mold on windows.

Table: How often to clean a humidifier.

The EPA says to clean the humidifier, as directed, at the end of the humidifying season or when the product will not be in frequent use, make sure all parts are dry before storing, and dispose of all used demineralization cartridges, cassettes, or filters. Don't pull a humidifier out of the closet in January and fill it without cleaning it first.

Tap water carries minerals, and ultrasonic and impeller units throw them into the air. The EPA notes some users see a white dust on furniture, which is a sign minerals are being dispersed. The EPA recommends low-mineral water: use bottled water labeled "distilled." Spring water and other bottled waters may still contain minerals.

The CDC adds a germ angle: to further reduce germ growth in humidifiers, use distilled water or boiled (and then cooled) water. The CPSC has said that while most humidifiers use tap water, distilled water is recommended by some. Distilled water reduces minerals and germs going in. It doesn't replace cleaning: mold can still grow in a tank of distilled water that sits for days.

CPAP machines have small humidifiers too. The CDC says most manufacturers recommend using distilled water for them and to clean the mask, humidifier and tubing regularly.

Most people who use a humidifier never get sick from it. But a dirty one can cause real illness in some people, and the EPA notes that the young, the elderly, and those people with lung diseases or respiratory allergies may be particularly susceptible to airborne pollutants.

What the sources say:

• Breathing problems. The CPSC has warned that microorganisms in the tank have the potential to cause respiratory problems. The EPA says breathing mist containing these pollutants has been implicated as causing a certain type of inflammation of the lungs.
• Humidifier lung. Doctors describe "humidifier lung" as a phenotype of hypersensitive pneumonitis, an immune reaction in the lungs linked to contaminated humidifier vapor, often during dry winters. A 2023 case report notes that, like other forms, it presents with cough, dyspnea, and fever. Avoiding the source is the main step.
• Humidifier fever. This is a shorter, flu-like illness. In a 1993 study of an outbreak at a print shop, a contaminated humidifier was linked to illness in 16 (57%) of 28 workers; the most common symptoms were myalgia, chills or subjective fever, and cough, and the illness lasted 2-24 hours. Home cases exist too: a German study of 14 people exposed to a home ultrasonic misting fountain diagnosed humidifier lung in 12 of them and humidifier fever in 2, according to the study abstract.

Both are uncommon, and neither is diagnosed by a mold test of your home. A doctor diagnoses them, and the 2023 case report's title makes the point: the key diagnosis is detailed medical history taking. The EPA's advice is direct: stop using your humidifier and contact your physician if you have respiratory symptoms you think are linked to it, even if you've been cleaning it. For more on how mold affects breathing, see mold and lungs and mold allergy.

Running a humidifier too high for weeks can leave mold on walls, window frames, closets and carpet. The EPA recommends keeping indoor humidity below 60 percent (ideally between 30 and 50 percent). Turn the humidifier off, dry the room, and clean small areas yourself.

In Texas, TDLR says areas of visible mold of less than 25 contiguous square feet can be cleaned up by people who are not licensed. For larger areas, use a licensed mold testing company to map the problem and a separate licensed removal company to fix it. Texas law says a license holder may not perform both mold assessment and mold remediation on the same project.

Find licensed mold testing companies in El Paso or Lubbock, and mold removal companies in Dallas, Austin or Houston. Browse all of Texas, check any license with our license check, and read how we verify every company.