Do Air Purifiers Actually Work? Here's What Experts Say

young woman in living room setting up home air purifier
Do Air Purifiers Actually Work?ArtistGNDphotography - Getty Images

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The best air purifiers work to improve the air quality inside your home, cleansing the air you breathe each day and limiting the impact that air pollution has on your family. And there are plenty of impurities that portable air purifiers can target in your house, including dust and pet dander, smoke and unwanted odors just to name a few.

In fact, indoor air can hold levels of certain pollutants that are up to five times higher than found outdoors. Air purifiers can indeed neutralize some of the risks posed by indoor air pollution — but not all purifiers are equally as effective, and many don't live up to their marketing hype.

While a well-designed appliance is key, even the best air purifier can't do it all. A good air purifier should be part of a multi-pronged strategy for maintaining healthy indoor air, not seen as a silver bullet solution. Working to reduce common sources of pollutants and increasing fresh airflow in your home are crucial strategies when it comes to lowering your air pollution risks, per materials published by the Environmental Protection Agency (EPA) — and a great air purifier can handle the rest.

How do air purifiers work?

Air purifiers usually consist of a filter, or multiple filters, and a fan that sucks in and circulates air. As air moves through the filter, pollutants and particles are captured, and the clean air is pushed back out into the living space. Typically, filters are made of paper, fiber (often fiberglass) or mesh, and they require regular replacement to maintain efficiency.

How frequently you will have to change filters varies based on the purifier type and usage. Some filters are reusable and washable, but they require meticulous maintenance, so you don't usually find them on the most effective air purifiers. Reusable filters are generally good at removing larger particles from the air, like dust mites and pollen. You'll also find UV (ultraviolet light) filters on the market, which often claim to destroy biological impurities like mold or bacteria; but many require higher wattage and greater exposure to be effective (not to mention some bacteria are UV-resistant).

That means, in addition to the purchase price of an air purifier, you should also factor in operating costs and filter replacement costs. Operational costs can easily amount to $50 annually, since you should be running air purifiers constantly to garner the benefits. Filter replacements can run upwards of $100 a year, all told.

Note that some air purifiers use ionizers to help attract particles like static — negative ions bond to dust and allergens and make them settle out of the air. If you're interested in buying an air cleaner that uses ionizers, make sure it does not produce dangerous levels of ozone, a gas made up of three oxygen atoms that is often marketed as helping break down pollutants, because ozone could be a lung irritant and further aggravate any asthma conditions.

Usually, air purifiers that emit ozone will have that listed on the packaging or in the marketing descriptions. For now, until additional testing and more robust industry standards are in place, our recommendation is to run any machine featuring plasma/ionization with those functions turned off. This is due to the fact that there is the potential for unknown harmful consequences, coupled with additional energy usage and a negligible or non-existent increase in purification.

What are air purifiers supposed to filter out — and can they actually do it?

Most filters on the market are designed to capture particles like dust, smoke and pollen, but they don’t catch gases like VOCs (volatile organic compounds) or radon that may accumulate from adhesives, paints or cleaning products. That would require an absorbent, like activated carbon.

In fact, EPA agents warn that the functionality of air purifiers is limited in terms of filtering out gases and that you must frequently replace filters for optimal functionality — usually about every three months. Allergens that are embedded into furniture or flooring are also not captured by purifiers.

Additionally, the effectiveness of air purifiers in real-world situations likely won’t mimic those of controlled conditions in a lab (which is what those "99% effectiveness" claims are referring to!). The location, installation, flow rate and run time for all will vary, as will the conditions in the space. There are also other things happening in your home that may affect the efficacy of a purifier, like ventilation (open or closed windows). New particles are constantly emerging, so the air might not be as filtered in reality as the claims may have you believe. And to remove allergens, bacteria or viruses that have settled on surfaces, you need to use disinfectant cleaners and/or effective vacuums.

Editor's Note: If you are concerned about mold, our experts recommend buying a dehumidifier or humidifier to help maintain the appropriate moisture levels in your home and stave off mold growth issues. Air purifiers do not prevent mold growth, so it is necessary to eliminate the source of moisture that is allowing it to grow.

Can air purifiers filter the outdoor air that enters your home?

Some models may be able to target bad air that creeps into your apartment or house, especially if you live in an area affected by pollution or natural disaster, like a wildfire. Most people shouldn't be worried about exposure to temporary pollutants like smoke or exhaust in the air outside your home, as they dissipate over time, explains Ryan Roten, D.O., an emergency medicine doctor with Redlands Community Hospital in California.

"In the short term, people will have asthma-like symptoms, primarily, or symptoms closer to allergies or sinusitis, including stuffy nose and a bit of a cough," adds Dr. Roten, who regularly treats patients with underlying respiratory illnesses. "If the smoke [from a wildfire] is dense enough, you might have some headaches due to carbon dioxide, and those with issues like asthma or COPD will have it worse in the moment."

Sometimes, non-organic air pollutants — like the VOCs discussed above — can originate from outside your home. "There are all sorts of scenarios in structure fires where large doses of smoke inhalation may lead to cyanide toxicity," Dr. Roten explains. "But that would largely need to be someone who was standing directly in or near a fire: Those people are brought to emergency rooms immediately. Generally, outside pollution or smoke or temporary bad air isn't a constant concern for bystanders."

But the right kind of purifier can address any environmental air impurities that may be overwhelming your community at the moment. Using wildfires as an example, Roten adds that a HEPA filter-equipped purifier is your best bet: "Anything that has a true HEPA filter in it is probably adequate enough to filter out most of the large particles that would be concerning," he says. "Most of the smoky smell will also be addressed as well."

What is a HEPA filter?

HEPA is an acronym for High-Efficiency Particulate Air. HEPA filters capture variously sized particles within a multi-layered netting usually made out of very fine fiberglass threads (much thinner than a strand of hair!) with various sized gaps. The filter is composed of a dense sheet of small fibers pleated and sealed in a metal or plastic frame. delivering the highest capture rates of airborne pollutants. Every model included in the Good Housekeeping Institute's rigorously tested guide to the best air purifiers you can buy has a true HEPA filter.

The air purifier's fan draws air into the filter and particulates are captured in the filter. The larger particles (ones bigger than the fibers) are captured via impaction (the particle crashes into the fiber), whereas mid-sized particles are captured by interception (the particle touches the fiber and is captured). The smallest, ultra-fine particles are captured by diffusion (while zig-zagging the particle will eventually hit and stick to the fiber).

Can air purifiers help protect against COVID-19?

Air purifiers that utilize HEPA filters can capture SARS-CoV-2 particulates, the virus that spreads COVID-19. However, the actual efficacy of an air purifier at preventing someone from getting the virus is still unknown, as the rate of transmission may be faster than the air purifier can capture the particulates. Therefore, we continue to recommend adhering to the CDC's advice regarding the best methods for reducing transmission risk and avoiding exposure to the virus as much as possible. This includes masking when possible, especially in crowded public spaces.

Should I buy an air purifier?

Before you do, know that an air purifier is not a cure-all. There is very little medical evidence to support that air purifiers directly help improve your health or alleviate allergies and respiratory symptoms. That’s due in part to the fact that it is difficult to separate the effects of known air-quality pollutants in your home from other environmental and genetic factors. (For instance, how are the furnishings and ventilation in your home affecting you in addition to any indoor pollutants?) But if you are an allergy- or asthma-sufferer, an air purifier with a HEPA filter may be helpful for you as it will be good at removing fine airborne particles.

What should I look for in an air purifier?

Finding the right air purifier in a sea of options can feel overwhelming. A majority of shoppers will need to weigh how big their space is (i.e. how much coverage you'll need), alongside which kinds of filtration they'll need to use and operating costs. If you're stuck between two or more options, try discerning which air purifier is better by looking at distinct manufacturing characteristics, including:

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What are other ways I can improve the air quality in my home?

The best advice is to address the source of indoor air pollution and to ventilate your home. If you are looking to supplement the work of your air purifier or see if you can get by without one, we recommended trying these steps to help reduce indoor air irritants:

  1. Keep your windows open when it's safe to do so to prevent locking irritants into rooms (especially when air purifiers aren’t running!). Create a stronger cross draft by opening windows on opposite sides of the room if possible.

  2. Vacuum often. If you are in the market for a vacuum, opt for one that is sealed, has a bag and is HEPA-certified. They’re better at trapping dust instead of sending it back into the air. We recommend the Kenmore Floor Care Elite Upright Bagged Vacuum.

  3. Regularly change air filters to properly maintain HVAC equipment and maximize effectiveness. Roten adds that, if suitable for your machine, sourcing a HEPA-specific filter for your circulation system can provide additional filtration: "It's [going to] recirculate the air in your house a bit better with each pass."

  4. Use an exhaust fan in the kitchen (and bath and laundry areas if possible). Switch it on before preheating the oven or firing up the burners, and leave it running for a few minutes after you’re done cooking.

  5. Minimize the use of candles. Do the same for wood fires and ban smoking inside your home — reducing pollutant sources is a surefire way to improve air quality.

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