Can Humidifiers Make You Sick – Infections And Pneumonitis

Around 45 million American use a humidifier to increase the moisture content in the air. Humidifiers are particularly essential in the wintertime, or in dry climates, for a comfortable environment. But do they have any adverse effects on health? 

Humidifiers can lead to health conditions, including microbial infections, sinus congestion, and humidifier lung by breeding germs (due to dirty filters, mineral deposits, inadequate cleaning, etc.) or by creating relative humidity levels that facilitate pathogenic growth.  

Humidifiers are a great addition to any home and play a crucial role in preventing allergies and respiratory issues that a dry environment may cause. However, using them incorrectly can have severe health implications. This article discusses humidifiers, how they work, and certain medical conditions associated with their use. 

What Is A Humidifier And How Does It Work

A humidifier is a device that imparts moisture to the environment. A humidifier generally works by: 

  • Using a water reservoir (bucket) to store water: While an evaporative humidifier uses a heating element to vaporize this water, an ultrasonic humidifier uses a metallic membrane that vibrates at an ultrasonic frequency (higher than 20 kHz) to produce mist. 
  • Inside the unit, a circulating fan rotates to draw dry air inside the system. The vapor/mist is then added to the air to increase its moisture content. 
  • Humidifiers have a built-in humidistat that detects the humidity levels of the room. It signals to the humidifier when to increase and then maintain the humidity to a preset level (selected by the user).
  • The humidifier periodically switches on and off to maintain the ideal humidity level as warm or cool mist is dispensed into the room.  

How A Humidifier Can Make You Sick

Humidifiers can cause various health conditions and under certain conditions (discussed later), they can breed germs as a result of their components and internal operating mechanisms (e.g., storage tank).

These germs are emitted with the air into the room.

Humidifiers may also create conditions (high humidity) that facilitate pathogenic growth outside the unit.  

Here are some of the health implications of humidifiers: 


Humidifiers can facilitate the growth of germs (bacteria, mold, and viruses), leading to various infections

Bacterial Infections

Bacteria are microscopic pathogens that are found everywhere – in soil, water, and our air. They carry over 40 diseases, which are typically transmitted via breathing and contact.

Common airborne bacteria caused by humidifiers are Salmonella, E. Coli, Klebsiella pneumonia, Staph aureus, Mycobacterium tuberculosis, etc. 

Bacterial infections may cause: 

  • Dysentery 
  • Diarrhea 
  • Fever 
  • Nausea and vomiting 
  • Muscle pain 
  • Chills  
  • Stiff neck 
  • Abnormal bowel movements 

Viral Infections

Viruses generally spread through close contact with the infected person. However, they remain suspended in the environment for some time, making airborne transmission possible. 

Humidifiers may breed viruses like Influenza, Herpes, Covid-19, Measles, Rubella, Common Cold, etc. They may infect us and cause symptoms like: 

  • High-grade fever 
  • Respiratory issues like Acute Respiratory Distress Syndrome (a condition categorized by low blood oxygen) 
  • Headache 
  • Swollen lymph nodes 
  • Organ failure 
  • Neurological damage (mental fatigue, confusion, seizures, etc.) 
  • Septic shock 

Mold Infections

Molds are complex, multicellular organisms that naturally exist in the environment as mold spores.

Spores can reach concentrations of more than 50,000 in a cubic meter. They produce toxins that can harm us when inhaled. Mold spores can also contaminate food and then infect us when the food is ingested.  

Some common molds that humidifiers may cause are Cladosporium, Penicillium, Aspergillus, etc. They can manifest as severe conditions like: 

  • Allergic reactions (wheezing, runny nose, itching, etc.) 
  • Damage to vital organs, especially lungs 
  • Exacerbation of asthma  
  • Skin, eye, and throat infections 
  • Impairment of intestinal functions 
  • DNA mutations 
  • Neurological and psychological damage 

Humidifier Lung

Inhaling contaminated moisture from humidifiers can lead to severe hypersensitivity.

A notorious condition that is linked to humidifier use is called humidifier lung – a rare type of pneumonitis. 

Pneumonitis is an inflammation of the lungs that is triggered by the immune system in response to germs and environmental toxins (smoke, pollens, dander, etc).

When constantly exposed to a large concentration of microorganisms or chemicals, our immune system goes into overdrive and starts killing our body’s cells (in this case, lung tissue).  

The injury impacts lung function, causing the following symptoms

  • Shortness of breath 
  • Fatigue  
  • Appetite loss 
  • Weight loss 
  • Temporary impairment of cognitive functions 

Initially, the natural healing system of the body repairs the damaged tissue. However, if the exposure to the toxins continues, the constant tissue injury leads to scarring of the lungs or pulmonary fibrosis. This implies that the lung tissue thickens and becomes stiff, making it difficult for you to breathe.  

Fibrosis is an irreversible, lifelong condition and can progress into the following severe diseases: 

  • Lung cancer 
  • Heart disease like cor pulmonale (damaged right ventricular wall)  
  • Perpetual brain fog (forgetfulness and inability to concentrate) 

Over time, the lung becomes susceptible to microbial infections, and can eventually lead to death. 


The sinuses are four paranasal cavities located in our head that warm the air we breathe in, reduce the weight of our skull, insulate our brain, aid in hearing, and even keep our nose clean.

Sinusitis refers to inflammation of the tissue lining these cavities.  

It is often caused by bacterial infections. A person exposed to moisture that is contaminated by bacteria is understandably more prone to developing sinusitis. It can present as

  • Runny nose 
  • Facial pain 
  • Headache  
  • Sore throat 
  • Bad breath 

Causes of microbial growth in a humidifier

Humidifiers need regular cleaning and upkeep. It draws in contaminated air and stores water, and the two factors can lead to a buildup of dust and germs. These germs are then emitted from the system and are dispersed around the home.   

Here are all the reasons why a humidifier may breed bacteria, molds, and viruses: 

1. Dirty Filter

All modern humidifiers have a generic filter that captures large particulate contaminants (particles) from the incoming air.

Over time, these filter pores become saturated and need to be cleaned to enable further filtration.  

This is compounded by the filter’s optimal lifespan, after which, cleaning becomes insufficient and it needs to be replaced instead. Although the filter life is mentioned in product manuals, sometimes a filter needs to be changed more frequently due to poor air quality. 

If replacement/cleaning instructions are not followed regularly, the filter fails to remove dust and debris from the air. These contaminants then accumulate inside the humidifier in the filter housing area, and breed germs. 


Here’s how you can clean the filter: 

  • Turn the humidifier off and remove the filter (usually present in the motor housing). 
  • Using a dry cloth or handheld vacuum to remove the dust and debris from the filter pores. 
  • If your user manual does not advise against washing the filter, rinse the filter under lightly running warm water – do not use detergent. 
  • Let it dry completely before placing it back. 

If the filter pores are swollen, severely clogged, or the humidifier frequently overheats replace the filter. A saturated filter interferes with the airflow, driving the unit under stress and increases the likelihood of overheating.  

2. Tap Water or Hard Water 

Humidifiers need water to increase the moisture in the air. This water is stored inside the reservoir and is directly propelled into the circulating dry air. The water is not filtered, so if unfiltered tap water or hard water is added to the tank, it causes the formation of scales. 

Hard water is rich in mineral content, especially calcium and magnesium. Tap water may also contain salts. While the water from the storage bucket is consumed for humidification, the minerals and particles in the water remain, and settle on the reservoir surface.  

Over time, the residue builds up and eventually forms hard yellowish scales. These minerals provide nutrition to the mold and bacteria, facilitating their growth.  


Using distilled (mineral-free) water will solve the problem.

Water Purification Guide has detailed information on brands of distilled water available here.

If distilled water is not readily available or you would prefer an alternate solution, use a demineralization cartridge in the water tank. It absorbs the minerals and salts from the hard water, significantly reducing the scales.  

Before each refill, it is crucial to descale, disinfect and clean the water tank. Here’s how to do it: 

  • After draining the tank, fill it with clean water. Let the water sit for a while and then empty the reservoir again.  
  • Prepare a white vinegar (1:1 part vinegar and water) or a bleach solution (1 tsp bleach in 1-gallon water), and fill half the tank with it.  
  • Let the solution sit for 20 minutes, and then drain the tank. Bleach and vinegar are strong disinfectants that can remove scales and kill bacterial colonies.  
  • Wipe the tank with a dry cloth. 
  • Keep rinsing the tank until the bleach/vinegar smell is gone.  

Note that some companies advise against using bleach as it is strong and can damage the reservoir surface.  

3. Old Reservoir Water 

Each humidifier has a specific runtime depending on the tank capacity. Usually, people let their humidifier run continuously for a few hours, and the entire tank of water is utilized for humidification.  

If the humidifier is not used for a few days, people tend to leave the leftover water in the reservoir for later use. But, since standing water is a favorable ground for microbial growth, the old reservoir water can make you sick.  


Drain and change the tank water at least every two days.  

4. Poor Air Quality Index (AQI)

The Air Quality Index or AQI is a scale used to gauge how clean or polluted the air is. While an AQI level above 100 is considered unhealthy, a humidifier filter can often cope with the amount of contaminant particles in the air.

However, in high pollution, the buildup of pollutants inside a humidifier is inevitable.  


Placing an air purifier in the room will resolve the issue. We recommend getting a HEPA air purifier, as it captures microscopic particles and pathogens (measuring up to 0.3 microns) with over 99% efficiency. This ensures that the air entering the humidifier is contaminant-free and disinfected. 

Also read about the pros and cons of using a humidifier and air purifier together here.

Other than this, you can also consider buying humidifiers with antimicrobial filters and sterilization techniques to ensure only clean air is emitted into the room.  

5. Corrosion 

The metallic membrane in ultrasonic humidifiers is essential to produce mist. This membrane comes in contact with unfiltered water and polluted air, which can lead to corrosion. The resultant rust can cause bacterial growth. 


If the rust does not go away after cleaning, replace the disc. Cleaning the disc frequently will prevent the issue in the longterm. 

It is important to note that once rust is established it will likely return, even if you have removed evidence of it. Cleaning it regularly will keep the humidifier in good working order and not expose you to airborne rust particles. However, replacing the disc is generally the best option.

How Humidifiers Cause Germs To Grow In The Environment

Before we dig into how humidifiers can cause pathogens to grow inside your room, it helps to know how humidity impacts the three main types of germs; bacteria, viruses, and molds. 

Humidity is a measure of moisture content in the air. In contrast, relative humidity is the ratio of how much water vapor is in the air compared to the maximum amount of water could be in the air (or its maximum water holding capacity).

A relative humidity of 30 to 50% is considered ideal. Levels higher or lower than this range are unhealthy and may lead to microbial growth. 

High humidity and high temperature often go hand-in-hand, and this combination suits bacterial growth. Above 60% humidity, bacterial metabolic processes are accelerated, and their growth rate is increased.  

The same holds true for molds. Mold cannot grow without humidity. In dry conditions, mold spores become dormant and do not sprout until relative humidity reaches above 55% (at 65 degrees).

On the other hand, viruses thrive in dry weather conditions (less than 40% RH), as it favors their survival and transmission. Research suggests that virus viability significantly decreases at higher temperatures and humidity. 

Humidifiers maintain the relative humidity at a preset level, which should be between 30 to 50%. However, humidifiers can sometimes have technical issues that can disrupt optimal humidity levels.  

A faulty humidifier can quickly turn a room into an ideal environment for microbial growth. Here are the most common causes of a faulty humidifier:

Faulty Humidistat 

A humidistat is a sensor that detects the humidity levels of the room. Once the humidifier attains the preset relative humidity, the humidistat temporarily stops the process to prevent over-humidification. When the humidity starts dropping again, humidification is resumed.

This way, the sensor helps regulate the moisture.  

If the humidistat breaks or stops working, it may cause humidity levels to rise or fall below the set level, both of which can influence microbial growth.  


You can use an ohm-meter to check if your humidistat is working. Attach the device to the humidistat and change the relative humidity gradually. If the ohm-meter needle does not deflect and constantly displays zero voltage, it implies that the sensor is broken.  

Call a technician and ask them to replace the sensor.  

Leaking Tank

Ultimately, the tank capacity determines the runtime of the humidifier. This reservoir is typically made of plastic, which can break or crack. Water can leak through the cracks and disrupting the entire humidification process.  


If you suspect a tank leak, you’ll likely notice water puddles around the humidifier. Inspect the tank for cracks – small cracks are usually fixable with adhesives.  Otherwise the tank will need replacing.

Broken or Displaced Float 

The float is a component in humidifiers that measures the water level inside the tank. Most humidifiers are programmed to turn off once the water bucket is empty. Since humidification cannot be carried out without water, this feature is crucial to conserve energy and prevent the unit from overheating. This entire process is regulated by the float. 

If the float is broken or not installed correctly, the unit can shut off sooner, preventing humidification (or not turn on at all).


After each refill, make sure to adjust the float according to the instructions given in your user manual. In case a float is broken, get a new one, and replace it to resolve the issue. 

Broken Fan 

The fan that draws air inside the humidifier is an integral component that determines the rate of humidification (by speed). If the fan breaks or its motor becomes damaged, it won’t rotate, and disrupts the inflow of air.  

Apart from impact and a malfunctioning motor, fan rotation is also hampered due to dust particles and clogs obstructing the blades. 


In the case of blockage in the way of the fan’s rotation, you will typically hear a grunting sound from the humidifier during operation.  

Refer to your user manual to disassemble the humidifier (make sure it’s turned off), and locate the fan. Try to rotate the fan manually, and if it does not move properly, clean the blades and remove any particles that may be disrupting the process.  

If there’s an issue with the fan motor, call a professional to fix it. Note that the motor is expensive and often requires replacement, even after minor damage. Therefore, if the warranty is not valid, purchasing a new humidifier will be more cost-effective than changing the motor.  

Malfunctioning Heating Element or Ultrasonic Disc 

The heating element or ultrasonic disc in humidifiers can start acting up. As a result, sufficient mist or vapors are not produced, and consequently, it takes longer for the humidifier to adequately improve the moisture level in the room.  


If you notice less than usual production of warm/cold mist from the humidifier and the fan, float, and humidistat are working fine, call in a professional and ask them to check the ultrasonic disc/heating element. 

Electrical Issues 

Frequent short-circuits can damage the humidifier components, interfering with the humidification process. New units or recently repaired appliances might have incorrectly placed wires, which also prevents the entire process. 


As a result of electrical issues, the humidifier either does not start or automatically shuts off a while into operation. If you notice either of the two problems with your unit, immediately call a professional technician to diagnose and fix the issue or call the customer service of your humidifier’s brand.

Benefits Of Using A Humidifier

If you clean the humidifier regularly and keep the relative humidity in check (between 30 to 50%), it can help improve your health. Here’s how: 

  • Reduce Allergies: Adequate moisture levels can soothe irritation and inflammation. Allergens like pollens, dander, dust, etc., primarily affect us when inhaled. By increasing humidity, humidifiers knock these allergens down onto surfaces, thereby reducing the risk of allergies.  
  • Relieve Asthma Symptoms: Asthma is a common lung disease that involves breathlessness, wheezing, chest tightness, and coughing. It is triggered by environmental factors, especially cigarette smoke.
    • Dryness can exacerbate asthma symptoms. Humidifiers improve moisture levels, thus keeping asthma at bay.  
  • Help With Sleep Apnea: Sleep apnea is a medical condition in which breathing periodically stops during deep sleep. This disorder is caused by a combination of diseases like pulmonary conditions, weak heart walls, obstruction in the respiratory tract, etc. The shortness of breath dries the mouth and trachea, leading to laborious breathing.
    • Humidifiers provide adequate moisture to the environment, keeping the respiratory tract moist, which aids in breathing air in and out. This is why humidifiers are a part of CPAP (Continuous Positive Airway Pressure) machines that are used to treat sleep apnea.  
  • Reduce Snoring: Snoring is associated with difficulty breathing. Multiple factors like sinusitis, allergies, cold, alcohol consumption, etc., can cause snoring.
    • Humidifiers keep the respiratory passage warm and moist, which can reduce snoring.
  • Prevent Infections: The ideal range of relative humidity keeps the microbes from breeding and impedes their growth, thereby significantly reducing the risk of infections.  
  • Maintain Skin and Hair Health: Moisture is crucial to keep the skin soft and supple. In dry weather, moisture is pulled from the skin, leaving it irritated. This can lead to wrinkles, redness, itching, and early aging.
    • The adverse effects of dryness don’t spare hair as well. In dry conditions, hair may appear frizzy and dull. The scalp may also release excess oil (sebum) that makes your hair look greasy. 
    • By improving the moisture level of the room, the humidifier protects hair health and rejuvenates the skin.  

Apart from this, a humidifier also protects plants. Dryness can cause wilting in plant leaves and inhibit overall plant growth. Therefore, a humidifier is essential, especially for topical plants.  

Is A Warm Mist Humidifier Better

Warm mist humidifiers do not have a specific germicidal mechanism (except if it uses a microbial filter or special disinfection technique). However, the water in their tank is boiled and can kill some germs.  

Note that this does not significantly affect the pathogenic exposure as filter health and condition of water and reservoir play a critical role in determining the quality of moisture dispensed out of the humidifier.  

Warm mist humidifiers also have a particular disadvantage over cool mist humidifiers because they consume more electricity to run the heating element. Therefore, there is no absolute answer for which type of humidifier is better at preventing germs.   

Russell Singleton

Russell holds a Bachelor of Science (Environmental and Marine Geoscience) with Class I Honors. He is currently completing his doctorate in science and is passionate about all earth processes, especially isotope geochemistry and paleohydrology.

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