Can a Humidifier Cause Mold? Crucial Tips For Prevention

Humidifier running in a lounge room during winter

Have you noticed greenish streaks, pink slime, black specks, or musty, foul odors when you use your humidifier? It could be mold.

Without proper use and maintenance, a humidifier breeds mold, just like a damp basement or a wet towel. Fortunately, preventing your humidifier from becoming a mold haven or mold-dispensing machine is easy. 

In this article, you’ll learn crucial tips you can take to stop mold from getting out of control and invading your home’s airspace—or your lungs.

Can a Humidifier Cause Mold in Your Home?

A humidifier can cause mold in your home in several ways. Let’s look at the situations you need to be mindful of to prevent your humidifier from promoting mold growth.

Overusing a Humidifier Leads to Dampness and Can Cause Mold in Your Home

Since a damp environment is essential for mold to thrive, overuse of a humidifier can cause mold in your home to grow excessively.

According to the United States Environmental Protection Agency (EPA), you should maintain an indoor relative humidity (RH) level between 30-50%.

Humidifiers are designed to increase the relative humidity in your home. However, it’s easy to take it too far and sometimes exceed the recommended levels, especially if the humidifier doesn’t have a built-in humidistat. Therefore, it’s essential to continually monitor the humidity levels with a hygrometer when operating a humidifier at home.

Although indoor humidity is typically higher in the summer, frequent use of air conditioning may suck moisture out of the air and render it dry. Heating your home during the winter also causes this problem.

You could experience itchy, flaky skin and dry eyes when indoor humidity is under 30%, which isn’t fun.

People may crank up a humidifier to counteract the lack of ambient humidity and improve their indoor environment. If they opt for a powerful large room humidifier, it’s easy to over-increase the moisture levels.

However, allowing a humidifier to operate 24/7 at full blast will unleash copious amounts of water vapor into your indoor air. Furniture, carpets, walls, and floors may become wet from excessive moisture. Relative humidity could quickly skyrocket above 70%.

When relative indoor humidity reaches 70% or more indoors for extended periods, mold “will almost certainly grow,” according to public health experts.

Poor Cleaning and Maintenance of a Humidifier Can Cause Mold in Your Home

Mold flourishes in places that are dark, damp, and warm. The water reservoir of a working humidifier often fits this description.

It is true that if you don’t run your filled humidifier frequently—or clean it regularly, mold will form. Days-old stagnant water inside the machine provides a perfect breeding ground for microorganisms.

When mold lives in your humidifier, the mold spores will be carried by water vapor or droplets into your home’s airspace during the normal operation of the device. This spreads mold to surfaces where it can jeopardize your health.

Fortunately, there are ways to minimize the likelihood of these mold-friendly conditions in your humidifier from ever occurring (see below).

Mineral Scale Buildup in a Humidifier Can Cause Mold in Your Home

Tap water contains a variety of minerals, such as magnesium and calcium. If you use tap water in a humidifier, the minerals left behind in the reservoir form a deposit are called scale. Note: ultrasonic humidifiers running on tap water may also leave a white mineral “dust” on surfaces in your home.

Since all living organisms need these minerals to survive, the scale buildup is a perfect place for mold and bacterial colonies to establish.

Fortunately, there is a quick fix to prevent scale in humidifiers (see below).

What Does Mold in a Humidifier Look Like?

Humidifier with visible mold
Mold growth in the base of a humidifier. Without routine cleaning, mold can grow in a humidifier.

The signs of mold in the water reservoir and pipes of a humidifier, include:

  • Black spots
  • Slimy streaks
  • Multi-colored growths
  • Pungent, stale or foul odors

When you actually see or smell mold, the problem is already advanced. It’s time to take action immediately to prevent it from getting worse.

Temperature and Relative Humidity Effects on Mold Growth

The EPA recommends an indoor relative humidity (RH) level of 30-50% to prevent mold growth. Does temperature have any effect on this recommendation?

Most mold species thrive at moderate temperatures (60-80℉) across a range of indoor humidity levels. Moisture control is more crucial than maintaining a cold environment for indoor mold prevention.

For example, a 2022 research study using the common mold, Cladosporium, showed that when the temperature was fixed at either 66°F or 82°F, this species had lower levels of activity and survivability at 40% RH compared with 60% or 80% RH.

The researchers concluded that indoor temperature does not affect mold growth as much as humidity levels. So, the general EPA recommendation of keeping indoor relative humidity at 30-50% to control mold growth is supported.

What Are Health Problems Associated with Mold?

Moldy air and exposure to mold can lead to or worsen:

Immunocompromised individuals, people with respiratory disorders, senior citizens, and children are most at risk from the adverse health effects of mold exposure.

What Is Mold?

A view through a magnifying glass of a wall with mol

Mold is a name given to many types of fungi. They are in the same taxonomic kingdom as mushrooms and yeast.

Mold species are nature’s decomposers, responsible for cycling nutrients from dead or decaying matter back to the soil, where this later becomes part of living organisms. Without mold, we would be up to our ears in dead plant and animal matter!

Indoors, it’s a different story. Some mold colonies live in dust or are free-floating in the air, often in a dormant stage. Mold reproduces in moist environments when a food source (such as paper or clothes) is present. Mold could become a health issue because of the toxic airborne substances (mycotoxins) it produces.

Mold enters your home in many ways:

  • Open doors, windows, or vents
  • Heating and air conditioning systems
  • Clothing, shoes, and pets

How Does Mold Grow?

Mold growth on the ceiling of a home near a window

Mold is present everywhere, usually invisible and dormant. However, under the proper conditions, mold reproduces by spores forming new colonies with threadlike filaments (hyphae) in a vast network called the mycelium.

The requirements for mold growth are:

  • Moisture
  • Oxygen
  • Warmth
  • Food sources, especially a carbon source (wood, carpet, etc.)

In homes, visible mold growth results from water damage:

  • Flooding
  • Sewage backup
  • Leaks or condensation (pipes, window, vent, or roof)
  • Damp basement, attic, or crawl space
  • Overflows from sink, shower, or bathtub
  • High humidity (potted plants, steam from cooking, humidifier, dryer, or showering)

How to Use a Humidifier Correctly to Prevent Mold

A woman controlling a smart humidifier in her home

The instructions below are based on the EPA’s humidifier care and use guidelines. If you adhere to the recommendations in our guide, it will make mold prevention in your home easier when you run a humidifier. Consistent and thorough cleaning and maintenance of your humidifier is key to a healthy home

1. Perform Routine Cleaning and Maintenance on Your Humidifier

There is much more to the regular upkeep of a humidifier than just adding water when it goes dry.

A good routine is to empty the tank, wipe all surfaces dry and then refill the water daily.

Make sure to unplug the humidifier before starting any cleaning or maintenance procedures.

You should thoroughly clean your humidifier’s tank and base every three days with an effective cleaning agent, such as distilled white vinegar (4-6% solution). If your humidifier requires deeper cleaning, you can use hydrogen peroxide (3% solution) instead to help disinfect and clean. Note: Never mix hydrogen peroxide with vinegar. The chemical reaction produces toxic vapors.

Swish the solution around and let it soak for approximately 10 to 30 minutes. Scrub away any debris with a small cleaning brush or a clean toothbrush, and wipe down the inside of the tank and base of the humidifier with the cleaning solution.

Rinse rinse thoroughly with several changes of tap water to prevent the dispersal of chemicals into the air. We recommend a final rinse with distilled water and then allow the unit to air dry.

If your humidifier has a wick filter, it will require regular maintenance. You can clean some wick filters with cool water by soaking and rinsing them and then allowing the filter to air dry before reinstalling it in the machine. Using harsh cleaning solutions can potentially damage the filter.

However, the filter should be replaced at least every three months, preferably between one and two months, depending on how often you use the humidifier and your water’s hardness.

When you’re going away for more than a few days or not frequently using your humidifier, sanitize and dry the machine. Then, dust it off upon returning and re-sanitize it before cranking it up.

Ultimately, when performing any maintenance, you should always follow the manufacturer’s instructions for the humidifier you have purchased.

If you end up with mold growth inside your humidifier device, read our extensive cleaning guide here to help you clean the mold out of your humidifier.

2. Maintain Indoor Relative Humidity Levels between 30 to 50 Percent

Set the humidifier’s built-in humidistat at 30-50% to prevent mold spores from germinating and leading to visible mold growth. A hygrometer can monitor your home’s humidity and confirm your unit’s internal reading. If there’s a difference between the two, you’ll know it’s time to troubleshoot.

To regulate the inside humidity, you may need to open windows. Similarly, adjust humidifier use along with the operation of your heating and cooling system. In cases where indoor humidity gets dangerously high (85% or more), you may need a dehumidifier to save the day and decrease the humidity in your house.

3. Keep the Area Around the Humidifier Dry

Preventing visible mold growth from the use of a humidifier requires observing its operation and making adjustments when needed. Too much moisture could lead to wet surfaces around the machine, which is never good.

So, lower the moisture output setting when you see damp walls, floors, or carpets and direct the mist to the center of the room. Alternatively, use the humidifier intermittently to prevent wetness. And wherever you notice moisture, use a towel to wipe it up immediately.

Ensure proper humidifier placement to minimize the possibility of wet furniture or carpets in a bedroom. Most importantly, position a humidifier at least three feet from the bed and two feet off the floor on a desktop, bench, or nightstand with a water-resistant tray underneath.

4. Use Distilled Water in the Humidifier

Use only distilled water to avoid mineral buildup (scale) inside your humidifier. Not only will cleaning be easier if you do. There won’t be any excessive minerals serving as a breeding ground for mold.

Plus, you won’t disperse minerals onto the furniture as fine, white dust. Distilled water will also extend the life of humidifier filters.

Final Thoughts

When appropriately used, humidifiers can do wonders for maintaining the EPA-recommended 30-50% relative humidity level in your home for your family’s optimal health.

However, mold may flourish inside the device if not cleaned regularly. It could then disperse mold or mold spores into your home, too.

Musty odors, spots, or streaks inside the humidifier are telltale signs that mold may already be thriving in your home’s air. Breathing mold-contaminated air could lead to or worsen numerous health issues, including respiratory disorders, allergies, or asthma.

Taking a few simple precautions can prevent mold problems associated with your humidifier. These include:

  1. Cleaning regularly
  2. Maintaining the recommended indoor humidity level (30-50%)
  3. Keeping the area around the humidifier dry
  4. Using distilled water

When you take these steps, you will help guarantee that your humidifier only adds moisture to indoor air without contributing mold or minerals to it.

Published: November 7, 2022

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