As the seasons change and the air becomes cooler and dryer, many people rely on humidifiers to keep their indoor air comfortable. While humidifiers have a lot of benefits, they’ve also been known to impact indoor air quality readings.  So, what’s the story? Do humidifiers help or hurt your indoor air quality?

The Good

A lack of moisture in the air can cause a variety of health problems including:

  • dry skin
  • irritated eyes
  • dryness in the throat or airways
  • allergies
  • frequent coughs
  • bloody noses
  • sinus headaches
  • cracked lips
  • snoring

Dry air has also been linked to higher rates of transmission of illnesses, including the flu and COVID.

Beyond the health benefits, humidifiers have also been shown to lengthen the lifespan of wood floors and furniture, prevent wallpaper from cracking, and keep indoor houseplants vibrant. Humidifiers may also help cut utility costs as humid air tends to feel warmer than dry air. Most experts recommend aiming for 30% to 50% humidity in your home at all times of the year.

The Bad

Unfortunately, when humidifiers turn on, air quality often goes down. But, why is that? Why would adding moisture to the air also increase pollutants?  The answer lies in how you are adding moisture.

There are two major types of humidifiers that work in very different ways: Ultrasonic and Evaporative.

  • Ultrasonic. Ultrasonic humidifiers contain a small metal plate that vibrates at an ultrasonic frequency powerful enough to break apart water particles. Water from the internal reservoir is broken apart into a cool vapor which is then distributed throughout the room as a fine mist.
  • Evaporative humidifiers. Evaporative humidifiers have been around for a long time and follow a very basic design. Air from the room is pulled in by a fan. The air passes through a moist wick filter at the bottom of the humidifier. When the air evaporates, it’s pushed back out into the room as a spray.

Why would either type of humidifier add pollutants to the air?

The most obvious reason is the humidifier itself.  If your humidifier, of either kind, is contaminated with bacteria or mold, your air quality monitor will likely pick up on these particles. However, there is another major factor that determines the number of contaminants in the air:

What form of moisture does your humidifier distribute?

Water vapors: Evaporative humidifiers release humidity in the form of water vapor. Water vapor is composed of purely H₂O molecules in their gaseous form.

Water droplets: Ultrasonic humidifiers release humidity in the form of water droplets. These droplets remain in liquid form so that whatever minerals in the water you put into the humidifier’s reservoir will be distributed around the room in the form of a hazy “white dust” and picked up by air quality monitors.

Research is still pending on how harmful white dust is. A study on mice showed that inhaling the dust from ultrasonic purifiers does produce a cellular response, but so far there has been no conclusive evidence to show that white dust creates the damage and inflammation caused by other harmful particulate matter such as PM 2.5.

While we do not yet know how white dust may affect your health, we do know that there are some key ways to keep the air quality in your home high, even while using a humidifier.

Switch to an evaporative humidifier.

While many prefer ultrasonic humidifiers for their sleek appearance, quiet operation, and lack of filters to replace, the easiest way to prevent a drop in air quality is to switch to an evaporative humidifier.

Use distilled water.

The fewer pollutants that are in your water, the less will be distributed into your home. Most tap water contains a variety of different minerals and contaminants. When the water evaporates, these contaminants are left behind. Distilled water, on the other hand, is pure H₂O. Whether you use an evaporative or ultrasonic humidifier, distilled water will cut down on maintenance and extend the life of your humidifier.

Maintain your demineralization filter.

If you opt to keep your ultrasonic humidifier, you can limit pollutants by using a demineralization cartridge. This is a ceramic filter that strips the minerals out of water. Most ultrasonic humidifiers come with these filters, but regular maintenance is required to keep them effective. Maintenance can vary by brand, but most need to be cleaned monthly and replaced annually.

Keep your humidifier clean.

Both types of humidifiers can collect bacteria, mold, and other pollutants which can then be released into the air and inhaled into your lungs. Consumer Reports recommends the following tips for keeping your humidifier clean.

  • Every day. Empty, rinse, and dry the base tray or reservoir before refilling.
  • Every week. Remove water scaling with vinegar, and disinfect the unit with a bleach solution following the manufacturer’s instructions.
  • Before storing. Clean to remove scaling, disinfect with a bleach solution, and dry thoroughly.
  • After storing. Before using again, clean to remove scaling, disinfect with a bleach solution, and dry thoroughly. Don’t fill it before you need to.

Purchase an air purifier.

A high-quality air purifier with a True HEPA filter will remove 99.95 % of all indoor pollutants, including any particulate matter that gets dispersed in the air from humidifiers. Besides keeping your air free of pollutants, research shows that a combination of a humidifier and an air purifier with a HEPA filter may be instrumental in slowing the spread of COVID-19.