Dehumidifier Mold Exposure

Mold growth inside of a dehumidifier tank

When performing indoor environmental investigations for clients, I like to teach them how to avoid dehumidifier mold exposure. Would you like to learn how? If so, this article is for you.

Dehumidifier being used in basement

People purchase dehumidifiers to reduce the humidity in their homes. They often purchase dehumidifiers for basements where high humidity is most common. The hopeful outcome is to protect indoor air quality and prevent mold growth in their home and on personal property.

When not used properly, as I discover in 8 out of 10 homes, dehumidifiers can be the cause of mold growth, and can actually spread mold spores throughout homes.

It’s too late

Unfortunately, many people put off purchasing a dehumidifier until AFTER they experienced water damage, a flooded basement, or have spent money on basement waterproofing.

Even more common, people purchase dehumidifiers after they’ve had high humidity for an extended length of time. At this point, there’s about a 100 percent chance hidden mold contamination already exists in their homes.

In some instances, people already know they have a mold problem. They’ve either seen some black mold or mildew or could detect a musty smell in the air. They dehumidify and often use air filters and air purifiers to try and trap mold spores. It’s too late. At this point, dehumidifying only temporarily stops the musty smell (digestive gasses) and active growth of mold because the mold simply goes dormant. It does not die or disappear.

Dry mold goes to sleep

Just like trees lose their leaves in the fall and go to sleep for the winter, mold goes to sleep when humidity leaves the air. When this happens, many molds release significant amounts of mold spores into the air as humidity levels drop. Mold releases spores that float through the air and spread to new locations. It’s a survival mechanism.

Using a dehumidifier, after mold growth occurs, is misleading. Dry mold will be present. Whenever the day comes that sufficient humidity returns, any pre-existing mold simply wakes up and starts growing and spreading again.

Remaining dry mold can still cause both allergy symptoms and asthma symptoms. Additionally, molds that are toxigenic can cause headaches, migraines, memory loss, ADD, and ADHD.

Moreover, pathogenic (infectious) mold spores that remain after dehumidification will continue to cause sinus infection, ear infection, and lung infection. Some doctors also believe infectious molds are a cause for many types of cancer.

For all these reasons, I thought it would be a good idea to write this article for you and others who may be researching dehumidifier reviews or looking for instructions on how to use a dehumidifier. I hope you benefit from it and share it.

 5 causes of dehumidifier mold exposure

There are many contributing factors to subtle, yet unsafe humidity levels indoors. Therefore, I encourage you to learn all you can about moisture sources and humidity control. All the vital information on these and other indoor air quality topics can be found in the store.

Indoor environments are relatively consistent no matter what climate you live in. This means that homes in any climatic region have the possibility of growing black mold, white mold, and species of other colors inside their homes that can result in mold symptoms.


The amount of mold growing in homes due to roof leaks, plumbing problems, and flooding, pales in comparison to the amount of mold growing in homes due to slightly high indoor humidity.

Now let me show you the five ways dehumidifier mold exposure makes people and pets sick.

 1) Are you guessing your humidity level?

Unfortunately, people only think to use their dehumidifier when it feels humid in their home or basement. Don’t guess – use a humidity gauge. Human perception should never govern dehumidifier settings. I have two gauges in my home and I keep my eyes on them all year long.

Dehumidifier with built in humidity gauge     Portable free standing humidity gauge

Some dehumidifiers have humidity gauges built into them. This helps in the vicinity of the dehumidifier, but if dehumidifiers for basements or crawl spaces are not in immediate view, then you should have a free-standing gauge in the primary area of your home to monitor indoor humidity.

  • Indoor humidity should not be lower than 25 percent RH or you’ll get shocks or nosebleeds.
  • Maintain indoor humidity lower than 50 percent RH to prevent mold growth.
  • An occasional spike above 50 percent typically won’t present a problem.
  • Monitor indoor humidity all year long to know exactly when dehumidification is necessary.

2) Are you turning your dehumidifier on?

This seems obvious, but let me explain. Far too often, I find dehumidifiers in mold-contaminated homes and basements sitting unplugged. Some people unplug them because they’re noisy. Others unplug them when conditions are dry, but then forget to plug them back in when needed.

Dehumidifier left in the box and the box grows mold on it

One of my clients purchased a brand new dehumidifier and left it in its unopened box. Personal property items throughout her home, including the box the dehumidifier came in, became severely contaminated with mold growth. She learned her lesson the hard way.

3) Are you cleaning your air filter?

I can’t tell you how many times my clients did not know their dehumidifier even had an air filter.

Dehumidifier dust screen filter hidden inside and plugged up

A dirty filter stops air flow through the dehumidifier allowing detrimental humidity to increase. Clogged air filters can also cause expensive mechanical damage to dehumidifier compressors.

  • Know where your filter is located
  • Check the filter every 30 days
  • The filters can be rinsed under a faucet or vacuumed clean.

4) Is there mold growing inside the water collection tank?

Black mold growth can hide inside of water collection tanks on dehumidifiers. Obviously, it is wet inside these tanks, so all it takes is some dust particles and one mold spore to start a contamination problem.

Mold growing inside of a dehumidifier water collection tank

As shown below, water that sits stagnant inside of collection tanks can also grow toxic bacteria that can make people extremely sick.

Toxic bacteria growing inside of a dehumidifier water collection tank

I had a client that was bedridden and her medical doctor recommended she contact me to have her home inspected for mold. What I discovered was that she was being poisoned by toxic bacteria growing inside of the dehumidifier tank. After I sanitized the water tank and ventilated the bacterial gas out of the house, she reported having a full recovery in a matter of days.

To prevent black mold or bacteria from growing in the water collection tank, I recommend entirely bypassing the water collection tank. You’re much better off using a hose connected directly to the dehumidifier condensation coil and have it empty into a floor drain. If a floor drain is not available, you can elevate the unit and have it empty into a sink or tub.

Dehumidifier water collection tank with hose attached to side

Most new dehumidifiers have hose attachments directly on the coils. If the hose attachment is on the side of the water collection tank like the one shown here, there will always be stagnant water in the tank.

5) Do you have mold growth above your water tank?

It’s common to discover black mold hiding on the underside of dehumidifiers directly above the water collection tank. I also find mold growing on the tops and sides of tanks.

Mold growing inside dehumidifier above water collection tank      Mold growing on top of dehumidifier water collection tank

The solution here is the same as above in that you should bypass the tank altogether.

If a dehumidifier has already been put into service using the water collection tank, it should be inspected for mold and sanitized. Effective mold cleaning solutions should be used, and as always, safe mold remediation techniques should be followed to prevent personal exposure or spread of mold spores.

DIY Mold Inspection

If you see visible mold and mildew, detect a musty smell, or have any mold symptoms that could be related to your home, read the Do-It-Yourself Mold Inspection series from

Book cover for DIY Mold Inspection book

In this series you will learn how to perform your own mold inspection without the cost of hiring a mold remediation company, spending money on mold testing, or risking a common mold scam.

I’ll walk you through every room in your home, including the attic, garage, and basement/crawlspace. Using inspection photos with explanations, I’ll show you why and where to inspect for mold, and how to see hidden mold when it’s the same or similar colors as the surfaces it grows on.

Once you learn the methods of proper mold inspection, you’ll likely be surprised to see how much mold is actively affecting your indoor air quality and putting you at risk of mold symptoms. Typically, whenever mold is discovered in one location, you’ll find black mold, white mold, and other colors of mold growing in additional locations.

Don’t waste your money on mold testing

I often get calls from clients wanting me to do black mold testing, In good conscience, I try to talk people out of paying me to do this work.

Microscope for mold testing

Mold testing is largely a waste of money. Knowing the species of molds you have in your home is basically useless information. Your goal should be to find ALL areas of mold growth and safely eliminate them from your indoor environment.

Similarly, while air filters and air purifiers can significantly improve indoor air quality in mold-contaminated homes, they are NOT a substitute for a mold inspection.

You could easily spend hundreds (or thousands) of dollars purchasing products, testing for mold, or hiring professionals to look at your home, and still risk becoming a victim of incorrect information or buying devices that will not solve your problems. Wouldn’t you rather have expert information from easy-to-read books that are only $7.99?

Mold Remediation

Whenever mold is discovered, before proceeding with DIY mold remediation or hiring a professional mold removal company, the responsible thing to do is to become familiar with proper and improper methods of mold cleaning. You can do this by reading the book Do-It-Yourself Mold Cleaning and Prevention.

Book cover for DIY Mold Cleaning and Prevention

In this book I will teach you how to:

  • make your own mold remover solutions
  • protect yourself from mold exposure while performing mold removal
  • prevent mold spores from spreading further around your home
  • avoid being scammed by mold companies should you wish to hire one
  • prevent mold from returning

Subscribe for more free air quality tips

You can receive quick reads of helpful information simply by subscribing. It’s a great way to continue learning ways to improve the air quality in your home.

About the author

If you would like to know why I’ve invested my life into helping people, you can visit About or read what others are saying by visiting Testimonials.

Share this page

Help your family and friends by sharing this blog page on social media.

26 Comments on “Dehumidifier Mold Exposure

  1. Can the black mold be inside the dehumidifier also? We’ve cleaned the filter, cleaned the tank and above the tank, where is was moldy. Now I’m afraid to turn it back in that we’ll have that smell in the house again!

    • Hi Kelly, it’s possible to have a few mold spores inside of dehumidifiers but they likely won’t be growing like they do in the areas shown in the photoes at the website. I wouldn’t be afraid to use your dehumidifier so long as you’ve cleaned the affected areas.

    • I’ve been using a cheap dehumidifier without any type of filter on In high moisture/ humidity basement and have emptied it many times while still running. Can I get mold spores in my lungs by doing this Stachybotrys was recently detected behind the base trim at a level of 112,000 cm2, also been sick with all symptoms for 2 1/2 of 3 years living here

      • Hello Bill,
        If you have mold growing on or inside the water collection bucket or above the bucket, as shown in the photographs, it is possible to liberate mold spores into the air when emptying your bucket. You could then inhale those spores and experience symptoms from exposure to them.
        However, dehumidifiers are often a contributing factor to health issues but rarely a single source. If your home is known to have that high levels of Stachybotrys, you likely have greater concerns within your indoor environment that are causing your illness. I would recommend a Zoom inspection to help determine the cause of your ailments. You can contact me directly at if you would like assistance.

      • Yes I took mine apart and found thick black mold growing on the grill inside. And I clean my filter every two weeks and also my water bucket. There is no way you can keep the dehumidifier from becoming mold infected itself. I have to buy one each year.

        • Kristie, purchasing a new dehumidifier every year is expensive compared to simply cleaning and sanitizing. Bypassing the bucket helps prevent problems but dust particles that collect on the grill, in the filter, or on internal surfaces can still grow mold. This is where using a residential air purification system helps. You can read about air purification in steps 5 and 6 in the book Breath Easy which is available on this website for $7.99. Stay healthy, Dan.

          • I cleaned the tank but am worried about the heat exchanger on a second hand dehumidifier . should I throw it away ?

          • Robert, dehumidifiers are expensive. If the unit still removes moisture from the air I wouldn’t throw it out. You can also wash the coil, just allow it to fully dry before putting the unit back in use.

        • I have a dehumidifier that gets a thick orangey-brown sludge in the spout that drips the water into the collection tank. Every time it gets full of sludge I get extremely sick with a fever and respiratory problems. Is this mold?

          • I doubt it’s mold. If what you see is within the water it is most likely bacteria. There are many types of bacteria. Some can be very unhealthy to be exposed to. When in stagnant water it is always a concern. I had a client that was bedridden from bacteria growing in her dehumidifier. Take safety precautions when cleaning and disinfecting the unit.

      • Hi Bill, sorry for the slow reply but the answer is yes. You can be exposed to mold spores anytime a mold-contaminated surface is even slightly disturbed. Addressing the moisture sources is better than relying on a dehumidifier. The second book in the DIY Mold Inspection series covers all the moisture sources and solutions.

      • It’s amazing all the places where mold can hide. That why I have been producing the DIY Mold Inspection books. 6 of 10 are completed and available on this website.

    • Kelly, if you clean and sanitize the inside of a dehumidifier correctly, there should be no smell. Using a residential air purification system helps with efficient sanitizing. You can read about air purification in steps 5 and 6 in the book Breath Easy which is available on this website for $7.99. Stay healthy, Dan.

    • Dehumidifiers only create problems when people do not use or maintain them correctly. To resolve your issues you need to discover your cumulative sources of moisture and eliminate or reduce as many as you can. The sources can be obscure so I recommend the second book in the DIY mold inspection series which explains moisture issues.

      • Hi Dan,

        My whole family are suffering from and under treatment for CIRS. I was wondering if there was any brand, or better yet specific dehumidifier models that you would recommend, which are not prone to developing mold and creating a problem in their own? I’m thinking one’s that have humidity gages, turn on/off when required, have a hose from the coil to drain off water, and most importantly are designed to prevent mold from building up on the coil and drain assembly (run a fan for a period of time after dehumidifying first awhile?). Anyways, any help or references in this regard would be very much appreciated.

        • Most all humidifiers today have the features you described but all of them are still prone to mold growth. It’s the nature of the appliance which is why they need to be monitored and maintained. Sorry to hear about your family. I have so many clients in the same shoes. If you have not read it yet, you would benefit tremendously from the book here on the website called Breath Easy.

  2. Hello,
    I have mold growing on the outside of my house (I rent half of a split house). My half o the house does not get sunlight and the mold is growing. I can see it on the window sills outside of my windows. Does this mean the mold is likely getting inside my house? In my bedroom, I have been sleeping with one of the windows open as it gets very hot and also with the air conditioner on; now I am thinking this is the cause of my horribly restless sleep, I have no problem falling asleep but toss and turn the entire night (not normal for me). I did shut the window, and also took the air conditioner out. I can’t see any visible signs of mold on the inside of the window but am wondering what I should do ? I also tested high for mold recently on urine test I did so I do have it in my system (its not normally high on the test for me). Would getting an inexpensive de humidifier help for my bedroom and some kind of cleaning of the indoor windows to be safe? Thank you so much !

    • Hi Diane, I usually do consults over the phone, but I’ll try to answer your questions here:

      It’s common for mold and black or green algae to grow on the shaded sides of homes. It does the same thing on the shady sides of trees. The mold you see on the siding is not the type of mold that causes most mold-related health issues that many experience today, and the house can be washed off for improved cosmetic appearance.

      Mold on the interior sides of windows and inside of window jambs is a different story. Mold on and around windows can cause a variety of health issues as shown and explained in the fifth book in the DIY Mold Inspection series.

      Sleeping with a window open is useful to allow entry of appropriate oxygen indoors to maintain health, healing, and clear thinking, but it has little bearing on mold. However, window and wall air conditioners can grow a lot of mold inside them that can affect health.

      A dehumidifier is a great idea to prevent mold but does not get rid of mold if you already have it. That is why you should perform a thorough inspection for mold.

      Tossing and turning can be due to toxic mold exposure but can also be caused by electrical radiation exposure. One or both can cause neurological malfunctions, including sleep disorders.

      I’m going to recommend that you read the book Breathe Easy – 6 Steps to Healthy Indoor Air. There are other books at that can help you learn more about indoor environmental health and how to see invisible mold. I hope this helps.

  3. Thank you for this post! Bypassing the water collection tank makes total sense. Could you please recommend a good dehumidifier with a proper hose connector, so no water will accumulate and there will be no concerns about mold in it.

    • Most all humidifiers today have features to prevent problems but all of them are still prone to mold growth. It’s the nature of the appliance which is why they all need to be monitored and maintained.

  4. Hi Dan, somewhat related: what do you think of alternatives like DampRid? I am using a dehumidifier but not in all rooms and I am looking for something small to put on my window sills so that I don’t have to manually dry all windows in the winter.

    • Hi Marie, DampRid works well in areas where there is no electricity such as a camper or storage room, but it is expensive for what it does, it is very corrosive if spilled, and bad for skin contact. Controlling indoor humidity and providing air circulation near the windows is the best solution. When below zero it is sometimes inevitable to stop moisture on windows and it needs to be wiped off daily until the weather warms up.

  5. Hi Dan,

    Thank you for this blog post. I do have a question. We just moved into a brand new house last year (built in 2020). We started noticing more humidity this spring began running our dehumidifier, which we have had for 3 years. It didn’t occur to us to inspect or clean it. We’ve been running it for the last couple of months but just noticed some black mold on the inside of the tank and even up inside the area around the filter. We didn’t feel like we’d be able to get it completely clean so we decided to toss the unit and will buy another one. My concern, however, is if we need to worry that we will get any mold contamination in our home? I don’t see any signs of mold on the walls or anything and we do pour bleach every few months in our central AC unit to prevent any blockages. Do we need to be worried or is there any precaution we can take right now to get ahead of this in case we have anything to worry about? Thank you!

    • Hi Kathrine, You’ll get mold in your new dehumidifier too so you might as well learn how to clean and sanitize them. My dehumidifier doesn’t grow mold and neither does my AC coil because I use an air purifier as described in steps five and six in the book Breathe Easy here at the website.

      You are putting bleach is in the AC condensate line I assume? Putting a 10-inch water-trap loop in the line and using clear tubing is best.

      In new homes, most mold that can be discovered right away will be found on the floor joists, in the box-sill cavities, and on the underside of the subflooring in crawls and basements. I show how to see it in the first DIY Mold Inspection book. Hope this helps you.  

Leave a Comment

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes:

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>