Air Purifier vs. Humidifier

Air purifiers and humidifiers have different functions. Air purifiers are clean indoor air, but do nothing for indoor humidity levels 3. They remove dust and smoke from the air, as well as allergenic substances like animal dander and pollen. Humidifiers add water into the air, but do not clean it. They are used to relieve health issues from dry air and help reduce static electricity in the home 2.

Air Purifiers

Air purifiers remove particles and other pollutants from indoor air. There are two main types of air purifiers: those that use mechanical filters to separate out particulate matter, and those that use electrostatic methods to trap electrically charged particles. Ionizers, which produce negative ions, create a negative charge on suspended particles, which then settle out of the air and stick to the next surface they contact, where they can be wiped up. Some air purifiers were found to produce ozone, which is implicated in producing inflammation of the respiratory system and worsening asthma symptoms. Ultraviolet, or UV, air purifiers kill bacteria and other pathogens and are commonly used in hospitals and day care centers. UV light purification has also become available in residential HVAC units

Mechanical Air Filters

Mechanical air purifiers use filters to remove relatively large airborne pollutants, such as dust and pet dander, from the air. Filters are often made from foam, pleated paper or polyester, or some other synthetic material. A high efficiency particulate air filter, commonly known as HEPA, is capable of removing 99.97 percent of airborne particles. HEPA filters can remove extremely small particles, but cannot remove odors. An air purifier may combine a HEPA filter with a charcoal filter to help reduce odors.


Humidifiers add water to indoor air, increasing the relative humidity of the indoor environment. Dry winter air can cause chapped skin and contribute to respiratory problems. Adding moisture to the air with a humidifier can reduce dry skin and decrease breathing problems, including lessening coughs. Adding humidity to indoor air can also reduce static electricity and prevent wooden furniture from cracking.

Types of Humidifiers

Four main types of humidifiers are ultrasonic, impeller-driven, evaporative and steam vaporizers 1. Ultrasonic and impeller humidifiers both produce a cool mist. Ultrasonic models are quiet because they use ultrasonic waves to produce mist, while impeller models use a rotating disk that can produce noise. Evaporative humidifiers use a fan to evaporate water into the air, and are also cold humidifiers 1. Steam vaporizers create a warm mist by heating water with an electrical element. Some models allow the mist to cool slightly before exiting the machine, and are known as warm mist humidifiers.

Humidifier Problems

The standing water in humidifiers can become home to a wide variety of bacteria, mold and fungi 1. When the humidifier is turned on, these organisms can be released into your home’s air, and breathing them can cause lung problems and even infections. In the past, disinfectants used with humidifiers have also created problems. Minerals from the humidifier’s water tank can be released into the air, where they settle out as a fine white dust. Humidifiers that use heat to evaporate water are prone to mineral build-up on the heating element, and the filters in evaporative humidifiers can also harbor bacteria and molds 1. You must keep humidifiers clean, and you need to occasionally descale them to remove mineral build-up.

Reviewed by: Tom Iarocci, M.D.

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