Last Updated: April 10, 2021

If you’re anything like Daniele Del Nero — which means you’re quickly aroused by the sight of millions and millions of molds consuming the load-bearing structures of any apartment, then turn on the humidifier during winter until you transform into a breathing braise of your own perspiration.

If you’re anything like me however — which means you’re quickly ruffled by the sight of molds hanging around the room curtains or the ceiling above, you want to be especially wary of how often you use the humidifier to treat the air.


Can humidifiers cause mold?

Yes, humidifiers can cause mold growth, but that’s when they are used unregulated that they end up raising the level of moisture indoors to one that easily supports such growth (usually above 55 percent relative humidity).

Rare portable humidifiers without a control humidistat are most likely the ones to cause such problems since they require manual monitoring by a human observer which isn’t going to be ideal.

Even portable humidifiers with built-in humidistats can also produce unreliable results since a vast majority of them are rarely accurate to the settings on the dial and can be off by as much as 10 to 20 percent.

In short, all humidifier can eventually lead to this problem if they’re not manually regulated in one way or the other.

This, in cold, warm, tropical or humid climate, can cause the humidifier to raise humidity level to far more than required and thus cause condensation on elements like walls and window sills which can easily harbor mold growth.

Another way in which air humidifiers can cause mold growth is if they are left uncleansed for an extended amount of time which ends up creating film or scum that act as breeding grounds for these microorganisms.

When the humidifier is run, it then disperses these microorganisms far and wide across the perimeters of the room where it is used, and the organisms can then easily find home on moist cottons, moist wooden furniture, or walls and window sills with condensation built up on them. From there, it’s only a matter of days before the presence of any living mold become known in those areas.

The mold growth problem can be especially pronounced when an individual lives in an area where the species of mold require a relatively low moisture content in the air to begin activities, and also when the temperature indoors is warm rather than cold which is optimal for most fungus to activate and begin reproduction.


Types of humidifiers and how they affect mold growth

There are generally two ways in which humidifiers can cause mold growth indoors. First is when they’re left to run unnecessarily, for long, or at excessive moisture settings which will cause an increase in the humidity levels around house (or room where they are installed) and then favor microbial growth, or when the standing water present in the humidifiers gets too dirty that it begins to create thin layers of scum which attract fungus like molds for feeding and breeding.

These organisms are then disperse during humidification which is the perfect time and condition for them to find residence in various materials around the house, especially wet and damp surface like wet laundry cloth or damp carpets.

The first point applies equally to all humidifiers that aren’t controlled by an automated system, and as for the second, it’s exaggerated mostly on the cold mist humidifiers such as ultrasonic, evaporative and the impeller types that generally contain a compartment for standing water.

Cold mist humidifiers are the biggest culprits when it comes to mold growth for the following reason.

They create cold mists and disperse them into the air which is excellent for spewing into the air, whatever microorganisms have already breed inside the standing water. For warm mist humidifiers, they revolve around “hot” or “steam”, and that is especially useful at ridding off microbes off already contaminated water before dispersing.

That’s isn’t to say that warm mist humidifiers like the steam vaporizers are completely safe when it comes to preventing mold growth around the house, it’s just to say that they are at least better in this regard!

When molds are disperse from contaminated standing water into the air, they usually cling to surfaces that are reminiscent of the medium they just left, which are warm, moist areas that are able to provide them food to eat. The typical examples are building materials made up of cellulose or plant fibers such as moist wooden walls, furniture and cotton curtains.


How to prevent a possible mold growth from humidifiers

In the first case from above, it’s very simple. Only use a humidifier when you really need it, because even those having humidistat can rarely keep to exact settings. That’s how humidifiers are meant to be used after all, not all year round.

Put humidifiers at the correct moisture setting while taking into consideration the current conditions of the room. This will help maintain the humidity at an acceptable range which is somewhere between 25 percent and 40 percent. You can always confirm and adjust the level of humidity within the four walls of any room using a hygrometer when the humidifier doesn’t have a built-in humidistat for automatic detection and control.

To dehumidify a room manually, use a dehumidifier, or an air conditioning system. For a manual method, ventilate the area to allow fresh air to enter so it can dry all damp and wet spots that can easily favor microbial growth.

For the second case, which is that of humidifiers with standing water, the solution is simple. Here’s what to do.


1) Clean the humidifier as per the manufacturer’s recommendation

This will prevent any buildup of scum which can promote growth of microorganisms. When planning on cleaning humidifiers, always refer to the owner’s manual for the instructions and also the recommended cleaning products or disinfectants. The manual will most often contain a one line sentence highlighted in bold which warns to always unplug the humidifier first before proceeding with any cleaning exercise! That inclusion is there for a reason! It’s shock!

If for some reason, you aren’t able to access your owner’s manual, below are some tips that you can use to properly clean your humidifier.

  • Use a 3% solution of hydrogen peroxide to clean all surfaces that come in contact with water i.e. the tank (inside, sides and base), filter, cap etc. Make sure to rinse thoroughly with water (about 2 to 3 times) and then dry completely to prevent any residue from making it into the standing water which will be used for later spraying.
  • Do now allow water to stand in your humidifier for an extended period of time. Replace water regularly to keep it fresh.  For portable humidifiers, it’s best to do this every day. Thoroughly empty the tank then clean every corner from the base to the sides, and then go ahead and clean the cap and other areas or components with the solution mentioned above or using the recommended cleaning agent by the manufacturer. Use a scrubber or brush for that purpose, but go gently to avoid scratches or damage. Also, make sure to clean and properly dry before components before refilling, and also before any long term storage and after taking out from storage to use again.
  • Check filters or cartridges regularly and replace them as per manufacturer’s instructions. When storing, it’s best to dispose of demineralization cartridges, cassettes, or filters.

Cleaning the humidifier and replacing water content regularly during the humidifying season will ensure that no harmful organisms are spewed in the air during use which may end up causing allergy or having consequential effects to vulnerable people.


2) Use water with less mineral content

Tap water contains too much minerals that can cause dispersal of allergy causing minerals into the air, often seen as fine white dust accumulated on surfaces. Besides, the minerals present also increase the development of scales which can become breeding ground for molds and other microorganisms and thus leading them to be dispersed into the air during the humidification cycle.

For that reason, the best water to use in your humidifier is distilled or demineralized water since most of the minerals have been removed from it. You can find that in bottled waters specifically labeled as such, and not those labelled with spring or artesian as they usually have not been treated to remove minerals.

Additionally, if your humidifier support the use of filters or cartridges or cassettes for filtering out minerals, consider using it when you don’t have access to distilled water. You should note though, that their effectiveness in removing minerals will vary wildly. You can check for effectiveness by observing whether or not white residue settle on items around the house after humidification session.

When opting for these devices, ensure that you properly change them on a regular basis to prevent accumulation of minerals which can end up causing the same effects as without the devices.


3) Eliminate any dampness near the humidifier to prevent mold growth

This include drying out windows, walls and window sills that have picked up condensation on them by ventilation. You can also turn down the humidification output volume to regulate humidity so items like carpeting, drapes, and tablecloths do not become too damp. If you can’t turn down the output of your humidifier, you can always reduce the frequency of use, or turn back to an air conditioning system to aid you. With a properly configured HVAC system, all these are in check.


How to remove existing mold growth at home

Use this guide here to do so.