Black Stuff In Your Humidifier: What Is It And Is It Harmful?


Black residue in or around your humidifier is caused by mold or the build-up of mineral deposits from non-purified or hard water. The humidifier should not be used until the black substance has been removed and the device cleaned, to prevent damage to the unit or a decrease in the indoor air quality.

Humidifiers help us breathe easier in the drier months, but if they’re not properly maintained, black stuff can appear around the humidifier, collect in the steamer or filter, or sink to the bottom of the water tank.

In this article, we explain the reasons for the black residue in your humidifier, how to fix it and what the best solutions are to prevent further issues.

What the black stuff in your humidifier really is

There are really only two causes of black residue in humidifiers:

1. Black Mold

Any water tank is a perfect habitat for breeding mold. Humidifiers have warm and moist interiors, which makes them extra vulnerable to this common household problem.

When humidity is too high and/or the humidifier is not cleaned regularly, this unpopular fungus will usually appear as black spots or blobs. Although mold isn’t always easily visible, a musty odor usually gives it away.

Mold is not necessarily toxic. Only when it contains mycotoxins does it has the potential to be fatal, but the presence of this compound is invisible to the naked eye.

The mold that usually appears in humidifiers is the garden variety type (the most common type of mold found inside and outside of homes) and it has no mycotoxins.

Still, non-toxic black mold can still create breathing problems and should be removed immediately.

Mold spores can also spread quickly onto other surfaces in the room, damaging your home and property.

So it’s important to treat and prevent any further development of mold in your humidifier (Keep reading for steps on how to remove this frustrating problem).

2. Mineral Buildup

If you’re using untreated or hard water from the tap to fill your humidifier, at some point you’re likely to find black specs in your unit’s tank.

This happens because some minerals, like calcium and magnesium, react when heated and turn into small black flakes that settle to the bottom of the tank.

This is more common in in warm mist humidifiers, where black sediment tends to build up as a layer of black coating over the heating elements.

Humidifiers filled with rainwater are equally susceptible to mineral deposit buildups. This is because rainwater contains copper and other types of minerals that turn black or dark brown when they come into contact with oxygen. 

When these minerals are released into the air with the humidifier’s steam, they are small enough to enter our lungs.

While no serious health concerns have been identified, the effects from inhaling this mist for a long period of time are unclear.

The accumulation of minerals or limescale in your humidifier obviously also lowers its performance, and it will struggle to humidify your room properly.

How to prevent mold and minerals in your humidifier

The best way to prevent mold or mineral buildup is to fill your humidifier with filtered or distilled water and clean it regularly.

Unfiltered water contains bacteria or minerals that both helps mold grow and limescale to form.

If you don’t have access to filtered water at home you can purchase purified water by the gallon, or demineralize tap water by simply boiling it on the stove.

The water in the tank should be changed daily, and every three days you should scrub the emptied tank with vinegar or citric acid powder. Remember to rinse and let it dry before refilling it.

Keeping your humidifier mold and mineral free also involves disinfecting it -including the base, wick and tank.

It’s best if you can disinfect your humidifier at least once or twice a month with a solution of bleach or hydrogen peroxide.

Add one teaspoon of liquid chlorine bleach to one gallon of water if you have a warm mist humidifier, or prepare a solution of 3 percent strength hydrogen peroxide for a cool mist humidifier.

You can purchase a 35 percent strength solution, the most common ‘food grade’ form of hydrogen peroxide, at a health food store, and dilute it by adding one and a quarter cups to one gallon of water.

NEVER mix bleach with hydrogen peroxide.

How to clean a humidifier properly

If you have mold or mineral deposits in your humidifier, remove them by cleaning it and then disinfect the unit to make sure it doesn’t re-establish.

  • Unplug the device and remove every detachable part, including the filter and water tank.
  • Wash the filter with plain water and the other parts with water and dish soap.
  • Wipe the entire external surface of the humidifier.
  • Pour one cup of white vinegar with another one of water into the water tank and swish it around.
  • Place the tank on the base and let the vinegar drain into the reservoir. Let it sit for a few minutes.
  • Remove the vinegar and use an old toothbrush to scrub any mold and mineral deposits from the water reservoir and any other area where the black particles have set.
  • Rinse everything with water and reassemble the pieces once everything has dried out, replacing the filter and filling the tank with clean, filtered water.  

Can mold in a humidifier make you sick?

Inhaling the steam from humidifiers contaminated with mold has the potential to produce allergens and irritants that trigger flu-like symptoms and, less likely, lung infections.

People with asthma and allergies are more sensitive to mold exposure, developing allergic responses such as fever, sneezing, runny nose, red eyes and skin rashes. Non-allergic people may still experience irritation in the eyes, skin, nose, throat and lungs. 

You may have heard of something called ‘humidifier lung’, an acute hypersensitivity pneumonitis caused by inhaling air from ventilation units -including humidifiers- contaminated with certain bacteria and fungi.

This disease is very rare and requires an exposure to high concentrations of toxic pathogens.

You would notice the dirt in your humidifier long before it escalates to such levels. 

Plentiful Air has more detailed information on how humidifiers can make you sick (and how to avoid this common problem) available here.

Highlights

The purpose of a humidifier is to improve the quality of the air indoors. It can also aid your respiratory system by reducing symptoms of hay fever and dryness in your nasal passages all the way to the lungs.

However, the incorrect use of your humidifier can actually do more harm.

Any contaminant in the device will pervade the entire space and enter your body.

It’s vital to keep moisture at its optimal level, use distilled water to reduce the risk of pollutants and maintain the unit regularly disinfected.

Take action as soon as you notice the appearance of any black stuff in your humidifier, and make sure you clean it thoroughly before storing when it is no longer in use.

Theresa Orr

Theresa Orr holds a PhD in Earth Science and specializes in determining past climates from rocks using geochemistry. Her passion for clean water, soil and air drives her to provide easy to understand information for everyone to read.

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