6 Ways Humidifiers Breed Bacteria – And How To Prevent It

Humidifiers are essential to prevent an uncomfortable, dry environment. However, given their inflow of polluted air and use of an internal water reservoir, it is natural to question if they can potentially breed bacteria.

Humidifiers that are irregularly cleaned, poorly maintained, or contain standing water for more than 2 days, can breed bacteria. Clogged or inefficient filtration, inadequate cleaning, mineral scales (use of hard water), and low air quality (AQI) contribute to bacterial growth in humidifiers.

If you live in a dry climate and rely on a humidifier to moisturize the air for comfort, it’s important to understand how and when your appliance breeds bacteria. This article explains how a humidifier internal mechanisms contribute to bacterial growth, and provides some related preventative measures.

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What Are Bacteria?

Bacteria are microscopic organisms found in every environment, i.e. soil, water, and air. Contrary to popular belief, bacteria are not always harmful. Some are present within our bodies and play a vital role in digestion and reproductive processes.

However, most airborne bacteria are dangerous and pose a risk for various infections and diseases. Here are some of the more common negative health effects of bacteria:

  • Pneumonia
  • Cancer
  • STDs and STIs
  • Cholera
  • Dysentery
  • Compromised immune system
  • Typhoid
  • Chronic inflammation

Apart from human health, bacteria are also disastrous for plants. They can lead to wilting, overgrowth, leaf spots, etc., causing the early death of the plant. Bacteria also deplete the soil of minerals that are needed for plant nutrition, thereby stunting plant growth.

Bacteria can even settle down on inanimate objects like furniture and home appliances and survive on the surface for three to ten days (or for months depending on species). This increases your chances of exposure to the pathogen.

6 Ways Humidifiers Develop Bacteria

A humidifier works by:

  • Drawing in the surrounding dry (and often polluted) air – either via natural circulation or by the help of a rotating fan.
  • The filters in the unit (not present in all humidifiers) trap the contaminants from the air.
  • Water is stored in a reservoir (bucket) inside the unit, and is used to produce mist.
  • While flowing through the system, air comes in contact with the mist and becomes humidified.
  • The humid air is the emitted into the room.

Humidifiers can breed and harbour bacteria in multiple ways. Once the bacteria has bred inside a humidifier unit, they become airborne and are dispersed around your space when the humidifier is operated.

We easily ingest these microbes and can become infected. In fact, humidifiers that contain bacteria (and other pollutants) are linked with a certain type of inflammation in the lungs, known as ‘humidifier lung’.

Here are the most common ways bacteria can develop in a humidifier and how to prevent them:

1. Clogged Filters

Some humidifiers have filters that remove dust, debris, and sometimes finer particulate matter and pathogens from the air as it flows through the system. These filters make the air safer to breathe and prevent the pollutants from depositing anywhere in the unit.

Each filter has a specific capacity and requires regular cleaning and replacement. If the filter is not changed regularly, its pores become saturated and unable to capture more airborne pollutants. This allows airborne pathogens (including bacteria) to accumulate and multiply in the humidifier.


Follow the filter maintenance instructions given in your user manual and clean/replace the filter accordingly. Vacuuming the filter or cleaning it with a dry cloth is typically preferred. Manufacturers usually recommend avoiding washing the filter as water and cleaning agents, such as soap or detergent can damage filter media.

Buying high-quality filters with a 7-10 MERV rating is also a great way to ensure efficient filtration and long filter life.

2. Inflow of Contaminated Air

In case of high pollution, the generic filter present in humidifiers is generally insufficient to remove the pollutants. If an air purifier is not run alongside humidifiers, airborne microbes and other contaminants enter and collect within the system.

While most of the bacteria flow along with the air out of the unit, some of them settle on the inner surfaces of the humidifier if the unit is not cleaned and descaled thoroughly; the bacteria buildup and breed into hundreds of colonies in a very short amount of time.


Most humidifiers use mesh filters with large filter pores. Although they can trap large-sized dust and debris, they are of no use against microscopic particles.

Running an air purification system along with a humidifier can remove contaminants from the air. Their filtration system is designed to trap and kill bacteria (True HEPA filter and UV light bulb) and prevent microbes from accumulating and breeding inside humidifiers.

Plentiful Air has detailed information on air purifiers that can remove bacteria available here.

3. Use of Tap Water or Mineral Water

One major factor contributing to bacteria build-up in humidifiers is using water that has a high mineral content. This can be tap water or well water that contains high quantities of magnesium and /or calcium ions.

Humidifiers produce mist or vapours from reservoir water to humidify the air. Once the water is depleted, the machine will shut-off until the bucket, or reservoir, is refilled.

The problem arises when mineral rich water, or hard water, is added to the tank. It contains a large concentration of calcium and magnesium minerals that deposit in the tank. Over time, these mineral deposits form a hardened clog or build-up, known as scale.

These blockages provide nutrition to bacteria and provide a favorable breeding ground for bacteria.


Demineralized or distilled water should be used instead of hard water. If you must use mineral water, frequently descale (not just clean) the tank. Also, make it a point to place a demineralization cartridge inside the tank to minimize scales.

4. Inadequate Cleaning

Adequate maintenance of a humidifier is essential to keep it running for a long time. When it comes to humidifiers, there is a higher chance of clog formation, or build-ups, due to insufficient filtration. These deposits are usually a combination of dust, debris, minerals, and airborne pathogens. It is incredibly important to thoroughly clean a humidifier at least once a week (when in use).

Understandably, if the deposits are not removed or effectively descaled, they lead to bacteria build-up.


Ideally, clean the filter weekly and rinse the water bucket before refilling. Descaling the humidifier when needed is also essential to prevent bacterial growth.

5. Old Reservoir Water

Humidifier manufacturers always advise emptying the reservoir water when the humidifier is not in use for more than 2 days. This is because a moist environment provides a favorable breeding ground for bacteria (and other germs).

A standing bucket of water naturally facilitates bacterial growth.


If you don’t use your humidifier daily, it is best to always drain its tank fully after use. Rinsing the tank before each refill is also crucial to prevent bacteria, mold and fungi growths.

6. Corrosion

Ultrasonic humidifiers use a metal diaphragm that produces high-frequency sound vibrations, propelling water from the bucket into the air. Iron-oxidizing bacteria present in the air can corrode the metal diaphragm. If the metal isn’t cleaned or replaced after rusting, bacteria continue to grow on it.


Rusting on metal diaphragm doesn’t only lead to bacterial growth but also shortens the disc life and reduces its efficiency. Cleaning the entire machine regularly is the only way to save the diaphragm from corrosion.

However, if rusting has already occurred, you must replace the diaphragm for adequate humidification.

How To Clean a Humidifier

Here’s how you can efficiently clean a humidifier to prevent bacteria breeding and to improve the unit’s optimal life.

Turn It Off

Always turn the unit off and disconnect it from the power source when cleaning or disassembling to avoid electrical accidents. This sounds obvious, but humidifiers contain water and use electricity, and shocks are a considerable risk.

Dust The Exterior

Take a clean, dry cloth and dust the external body of the humidifier. Avoid using water if you can, but if there are stubborn marks (etc) on the outside you can use a damp cloth – simply dry the unit with a towel before cleaning the inside of the humidifier.

Clean/Replace The Filter

Filters are typically located inside the motor housing of humidifiers. Take out the dirty filter and use a vacuum or dry cloh to remove the dust from it. If your user manual doesn’t explicitly recommend avoiding rinsing, you can also wash the filter with warm water, but don’t use any soap or detergent as this can degrade the filter.

Mesh filters should usually be replaced every three months. However, depending on the pollution, you may need to change the filter sooner.

Since humidifiers generally don’t have filter change indicators, you can look out for the followings signs to know if your humidifier filter is saturated:

  • Clogged or excessively dirty filter
  • Swollen filter pores
  • Humidifier overheats frequently

Descale and Disinfect

Descaling implies cleaning an appliance to remove scales (deposits, crusts or layers formed by minerals, that are often combined with dust, and other particulate matter).

Disinfecting means cleaning with a chemical (not just water) to kill/eliminate bacteria and other microbes.

To descale and disinfect a humidifier:

  • Empty the tank water and fill it with clean, room temperature water. Let the water sit for a few minutes and then drain.
  • Prepare a vinegar solution (1:1 part vinegar and water) or a bleach solution (1 tsp of bleach in a gallon of water) and fill the tank with it. Make sure to check if your user manual advises avoiding bleach.
  • Let the solution stand in the tank for 15-20 minutes and drain.
  • Wash the reservoir and keep rinsing until the bleach/vinegar smell is gone.

Bleach and vinegar are highly effective at breaking down encrusted deposits. They also act as strong disinfectants by killing bacteria and reducing their growth.

After draining the vinegar from the tank base, use a dry cloth to remove any mineral and dust deposits from it. Then rinse it with fresh water to eliminate the smell of the vinegar.

For descaling the nozzle and tank lid, dip them in the base vinegar solution for 15 minutes, and then clean, rinse and dry them to reassemble.

Unless the user manual has other related instructions, using a vinegar solution is typically the best to descale and disinfect a humidifier.

Humidifiers That Are Least Prone to Bacterial Growth

While all humidifiers can cause bacterial growth, units with antibacterial filters can prevent microbial breeding by filtering out maximum pathogens from the incoming air. If regular cleaning of the tank and other components is taken care of, these antibacterial humidifiers naturally become less prone to bacteria build-up.

Demineralization cartridges and air purifier-humidifier combo units can also prevent bacterial multiplication.

Here are three of the best antibacterial humidifiers (available on Amazon):

1. MistAire Eva-Mist-Free Evaporative Humidifier

PureEnrichment is a popular brand in America, and its appliances are known for quality and reliability. Their MistAire Eva is an evaporative humidifier that employs a heating element to produce water vapors that are then sent into the air.

It comes with an easy-to-install antibacterial filter that traps allergens (pollens, dust, etc.) and bacteria. The filter is also coated in antibacterial material to improve its optimal life.

The humidifier caters to 500 sq. ft. of space and is an excellent choice for small to medium-sized rooms.

2. TotalComfort Deluxe Warm and Cool Mist Ultrasonic Humidifier

The TotalComfort Deluxe Warm and Cool Mist is an ultrasonic humidifier that generates visible mist to humidify the air. It comes with a demineralization cartridge that can be placed in the water tank to prevent inorganic deposits, thus limiting bacterial growth.

It also comes with a Clean Tank Technology that makes it easy to drain and clean the water tank. Easy maintenance benefits the user while simultaneously reducing the risk of bacterial breeding.

Its 1.38 gm top-fill water tank provides an 85-hours runtime. Covering an area of almost 521 sq. ft. This humidifier is a perfect fit for complete medium-sized room coverage.

To add to it, the package also includes essential oil tray pads that dispense fragrance along with pure mist into the room. 

3. Afloia Miro Pro 2-in-1 HEPA Air Purifier With Humidifier

Afloia 2-in-1 is a humidifier and air purifier combo device. With the air purifier being the system’s main body, this unit provides three-tier filtration (comprising pre-filter, HEPA filter and an activated carbon filter) for over 99% removal of airborne contaminants.

This minimizes the entry of pollutants into the humidifier section, thus reducing the chance of bacterial buildup.

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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