Dehumidifier vs air purifier: What’s the difference?

person switching on a dehumidifier
(Image credit: Getty Images)

If you struggle with uncomfortable respiratory symptoms, you may be wondering what the difference is between a dehumidifier vs air purifier? Both can be helpful in controlling troublesome symptoms of conditions such as allergies and asthma, but how do they work? And is one better than another for certain conditions? 

Air purifiers differ from dehumidifiers because they actually clean the air and trap pollutants and allergens, whereas a dehumidifier’s purpose is to alter the humidity levels of indoor air and remove any excess moisture.

We’ve spoken to a medical doctor and an associate professor of indoor air quality to get their views on dehumidifiers vs air purifiers. If you’re looking for the best air purifiers, or for the best dehumidifiers, we’ve also tested and reviewed some of the top models available on the market to make your choice easier.  

Dehumidifier vs air purifier: What do they do?

Dehumidifiers work by extracting moist, warm air from the environment and cycling cool, dryer air back into your home. They can help to control the humidity in a room and can reduce condensation and damp, in turn reducing the risk of a space developing mold.

Air purifiers, on the other hand, do not change the humidity levels of a room and are instead designed to filter indoor air pollutants such as pollen, smoke and dust out of the air and cycle clean, pollutant-free air back into your home.

Wei-Ning Wang, an associate professor of indoor air quality and aerosol technology at Virginia Commonwealth University, outlines the main role of each system.  “Dehumidifiers are essential tools, in particular in summer, to lower the relative humidity (RH), which in turn could reduce mold growth and hence increase air quality,” she says. “Air purifiers are to capture and remove airborne particles including molds to enhance air quality.” 

Dr Wei-Ning Wang
Dr. Wei-Ning Wang

Dr. Wang is an associate professor in the Department of Mechanical & Nuclear Engineering at Virginia Commonwealth University. He covers a wide range of topics in nanomanufacturing and nanotechnology, addressing critical challenges in the sectors of energy, the environment, and human health. 

Dehumidifier vs air purifier: What are the benefits?

A dehumidifier can be particularly useful if you live in a damp environment and find that the moisture in the air causes issues like condensation and mold. If you’re not sure what humidity is comfortable, Dr Deborah Lee, a medical doctor and representative for Dr Fox Online Pharmacy explains more to Live Science. “If the air is too humid, this can precipitate house dust mites and mold, triggering asthma symptoms” she says. “Humid air directly triggers the airways to constrict, resulting in allergens being trapped inside, and worsening asthma symptoms.”

Air purifiers can also aid those with respiratory conditions, by removing allergens from the air before they can be inhaled. “Exposure to a wide range of indoor allergens is known to trigger asthma,” adds Lee. “These allergens include house dust mites, household pets, cockroaches, mold, and mice. One solution may be the use of air filtration mechanisms. These may be installed as an integral part of the home’s heating or air conditioning system, or air filtration can be achieved using portable machines, such as a High-Efficiency Particulate Air Filter (HEPA).”

Happy couple use air purifier

(Image credit: Getty)

Dehumidifier vs air purifier: What can they help with?

The two main issues that both dehumidifiers and air purifiers can help with are allergies and asthma, which are often related. So, how do dehumidifiers help with allergies? And are dehumidifiers good for asthma

A study in the journal Clinical and Experimental Allergy indicates that low humidity environments can be helpful in controlling dust mite populations and therefore reduce the burden on those with allergies and asthma. A Chochrane review also indicates that more evidence needs to be collected to definitively say whether a low humidity environment can help with asthma, however their use did lead to a decline in the house dust mite count and the antigen level.

dehumidifier in an apartment besides some plants

(Image credit: Getty Images)

The evidence supporting that air purifiers help with allergies and also help with asthma is more robust. A 2021 study in Allergologia et Immunopathologia (a Spanish medical journal) showed a reduction in particulate matter and dust mites when an air purifier with a HEPA filter was used. A review in Current Allergy and Asthma reports also indicates that air cleaners and air filters (air purifiers fall within these categories) can reduce the burden of allergies and asthma symptoms on those who suffer chronically. 

Dehumidifier vs air purifier: Which is right for you?

If you live in an area with high outdoor pollution (such as near a road) or you live with someone who smokes, you might want to consider purchasing an air purifier. 

Lee encourages investing in a system with a HEPA filter. “Choose a HEPA filter that has a high level of efficiency: to be effective the device should remove 99.97% of particles that measure 0.3 nanometers or larger in diameter,” she says. “The HEPA machine should be powerful enough to replace the air volume of the room 2-3 times an hour. Don’t use an ionizing air purifier as this produces ozone which is known to worsen asthma symptoms. Reduce environmental triggers by hoovering regularly – twice a week or more with a hoover with a HEPA filter.”

If your house is particularly damp, you frequently have excess condensation on windows or cold surfaces, or you struggle with mold, then a dehumidifier might be the better option for you. However, to remain effective you must remember to clean your dehumidifier, as Lee explains. “Without cleaning, it can be a breeding ground for bacteria and viruses which it then releases into the air, and this can make asthma worse. Also, the chemicals needed to clean it are then released into the air and again can trigger symptoms,” she says. “A dehumidifier will reduce dampness and mold but cannot remove these completely.”

Lou Mudge
Health Writer

Lou Mudge is a health writer based in Bath, United Kingdom for Future PLC. She holds an undergraduate degree in creative writing from Bath Spa University, and her work has appeared in Live Science, Tom's Guide, Fit & Well, Coach, T3, and Tech Radar, among others. She regularly writes about health and fitness-related topics such as air quality, gut health, diet and nutrition and the impacts these things have on our lives. 

She has worked for the University of Bath on a chemistry research project and produced a short book in collaboration with the department of education at Bath Spa University.