Sarah Bence, OTR/L, is an occupational therapist and freelance writer.

Daniel Combs, MD, is board-certified in sleep medicine and pediatrics.

Air purifiers are devices that filter air quality. They are helpful for people with allergies, asthma, and other respiratory or cardiovascular conditions. There are an overwhelming number of options, features, and brand names on the market, so it's difficult to know not only which one to pick, but if it's worth picking one at all.

Air purifiers do work to filter pollutants from the air, but there are limitations to be aware of. In this article, you'll learn about how air purifiers work, benefits, and factors to be aware of.

On average, Americans spend 90% of their time indoors, and just like the outdoor world, there can be pollutants in your home. In fact, some of these pollutants are up to five times more concentrated indoors than outdoors due to:

The purpose of an air purifier is to filter and sanitize these pollutants, chemicals, and allergens from the indoor air and improve air quality.

HEPA stands for high efficiency particulate air filter. It is one of the most effective and studied air purifiers on the market.

It can capture extremely small particles of 0.3 microns or larger. Theoretically, HEPA filters can remove 99.97% of airborne dust, bacteria, mold, pollen, and other particles, although in reality its effectiveness will depend on factors like the age of the filter.

Research has shown that HEPA filters are highly effective at removing fungi, mold, and other allergens from indoor air.

HEPA filters are highly in demand because they are effective at removing airborne COVID-19 virus. However, a HEPA filter or other air purifier alone is not enough to protect you from COVID-19 infection. You should follow CDC guidance to prevent contracting or spreading the virus.

Ionic air purifiers tend to be less costly than HEPA filters, so people may opt for them for this reason. However, there are some important things to be aware of regarding their effectiveness and health impacts.

Ionic air purifiers work by emitting large amounts of electrically charged negative ions into the air. In the same way that static works, these ions attach to particles in the air (such as mold, allergens, and chemicals) and ground them to surfaces like the floor or walls.

While this improves air quality, these particles remain, and may be recirculated to the air the next time you sweep, sit on the couch, lean on a wall, or walk across the floor.

Additionally, research has shown that the negative ions sent out by ionic air purifiers can have negative health consequences by increasing systemic oxidative stress. The researchers concluded that the drawbacks of ionic air purifiers do not outweigh their benefits, and did not recommend their use.

Many air purifiers work through a system of filtration to remove particles from the air and recirculate clean air. The exact mechanism of how this is done can differ between different brands and types of air purifiers.

In its basic form, an air purifier includes a fan that draws in nearby air. This air passes through a filter, which can be made from various materials such as paper or fiberglass.

The filter then traps particles above a certain size. This size will differ between air purifiers. For example, a HEPA filter is the highest standard and can trap particles greater than 0.3 microns in size.

Finally, the filtrated, clean air is then recirculated to the room through the fan. Over time, however, the filter will need to be replaced.

Keep in mind that not all air purifiers work in the same way. Some air purifiers work by neutralization, instead of drawing in and filtering air. For example, they may send out negative ions that attract particles through static, and neutralize them.

Ultraviolet light (UV) filters are another kind of air purifier. They work by sending out UV light to kill bacteria and mold.

The goal of air purifiers is to reduce our exposure to certain irritants by filtering them out of the air and improving air quality. The theory is that this will lead to health benefits.

Some of the studied health benefits of air purifiers include:

Yes, air purifiers do work, but with some caveats.

In reality, the benefits derived from air purifiers will depend on many factors, including:

Air purifiers work best in combination with other cleaning techniques at home, such as:

The term allergens refers to generally harmless substances that may trigger an allergic response in some people. Indoor airborne allergens can include:

Some air purifiers are effective at filtering allergens from the air. HEPA air purifiers, in particular, have been shown to be effective.

In one study, HEPA air purifiers significantly decreased allergen concentration (which was predominantly dust mites) in both the air and bedding. The participants, who all had allergic rhinitis, also showed symptomatic improvement in nasal and eye symptoms and activity limitation.

Another study found that among schoolchildren with allergies, HEPA air purifiers were effective at improving pulmonary (lung) function and reducing allergy symptoms of runny nose and inflammation.

Fungi, which includes mold, mushrooms, and yeast, can be an allergen for many people. One study found that a HEPA air purifier fan was effective at reducing airborne fungi within homes.

Smoke is a big concern regarding indoor air pollution. Smoke may be produced from:

One study found that portable HEPA filter air cleaners were effective at reducing secondhand smoke exposure among non-smokers.

Another study among smoking households with non-smoking pregnant people found that while the HEPA air purifier reduced particulate matter in the air, it did not reduce air nicotine. Secondhand smoke exposure was reduced—but not eliminated—among the pregnant people. It did not change among the infants.

Ultimately, smoking cessation is highly preferred over the use of air purifiers. The United States Environmental Protection Agency (EPA) also recommends ventilating with clean outdoor air, if there is indoor smoking.

Other indoor toxins, such as chemicals produced by cleaning, personal care products, or building materials, are also a concern.

Research shows that HEPA air purifiers can reduce indoor toxins produced by 3D printers, although it is more effective if the filter is built into the printer itself.

Photocatalytic oxidation is another kind of air purification technique that has a role in reducing airborne toxins. This type of air purifier uses the energy produced by UV light to begin a chemical process to neutralize and destroy particles in the air.

Research shows this kind of air purifier can remove chemicals like formaldehyde , acetaldehyde , and toluene from the air.

You may choose to purchase an air purifier to help improve your indoor air quality. Here are some things you should look for as you choose the best air purifier for you:

It is recommended to use an air purifier in combination with other methods to manage your indoor air quality. Some other things to try to improve your indoor air quality include:

Air purifiers are effective at reducing the particulate matter in the air. Some types can lead to health benefits for those with allergies, asthma, and other conditions. However, there are many factors to consider when choosing the most effective air purifier. HEPA filters have the most research to support them and can filter extremely small particles.

Most people spend the majority of their time inside, so indoor air quality can be a major concern. This is especially true for people with allergies or asthma, who may be reacting to airborne pollutants in their homes. Air purifiers can reduce these pollutants and help you feel better, but not all air purifiers are created equal. You should consider the type of air purifier, the size of the indoor space, MERV rating, and how often you'll need to change the filter.

Ionic air purifiers emit large amounts of negative ions into the air. In the same way that static works, these ions attach to particles in the air (such as mold, allergens, and chemicals) and ground them. However, there can be negative health consequences to ionic air purifiers that negate their value as an air purifier.

Aim to put your air purifier where there is air flow, and where you believe there is a high concentration of pollutants. For example, place it on a side table, mount it on the wall, or place it near a door or window. Do not place it in a corner blocked by a TV or shelves.

The cost of air purifiers can vary greatly, from $50 to hundreds of dollars. You should also budget $50-$100 for annual filter replacement.

It is often recommended to run an air purifier for 12-24 hours a day. You should check the manufacturer guidelines. Additionally, frequently vacuuming and cleaning can improve the life of your air filter.

An air purifier draws pollutant particles out of the air, whereas a humidifier adds moisture particles to the air.

How long an air purifier lasts will depend on the particular brand, model, and level of air pollutants. However, many air purifiers last a full year before a filter must be replaced.

Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life.

Thank you, {{form.email}}, for signing up.

There was an error. Please try again.

U.S. Environmental Protection Agency (EPA). Indoor air quality.

U.S. Environmental Protection Agency (EPA). What is a HEPA filter?.

Hashimoto K, Kawakami Y. Effectiveness of airborne fungi removal by using a hepa air purifier fan in houses. Biocontrol Science. 2018;23(4):215-221. doi:10.4265/bio.23.215

U.S. Environmental Protection Agency (EPA). Will an air cleaner or air purifier help protect me and my family from COVID-19 in my home?.

Liu W, Huang J, Lin Y, et al. Negative ions offset cardiorespiratory benefits of PM2.5 reduction from residential use of negative ion air purifiers. Indoor Air. 2021;31(1):220-228. doi:10.1111/ina.12728

Chen Renjie, Zhao Ang, Chen Honglei, et al. Cardiopulmonary benefits of reducing indoor particles of outdoor origin. Journal of the American College of Cardiology. 2015;65(21):2279-2287. doi:10.1016/j.jacc.2015.03.553

Yang X, Wang Q, Han F, et al. Pulmonary benefits of intervention with Hepa air purifier in schoolchildren: a double-blind crossover study. SSRN Journal. 2021. doi:10.2139/ssrn.3790393

Jia-Ying L, Zhao C, Jia-Jun G, Zi-Jun G, Xiao L, Bao-Qing S. Efficacy of air purifier therapy in allergic rhinitis. Asian Pac J Allergy Immunol. 2018;36(4):217-221. doi:10.12932/AP-010717-0109

Barn P. The effect of portable HEPA filter air cleaners on indoor PM2.5 concentrations and second hand tobacco smoke exposure among pregnant women in Ulaanbaatar, Mongolia: The UGAAR randomized controlled trial. Science of the Total Environment. 2018;615:1379-1389. doi:10.1016/j.scitotenv.2017.09.291

Rice JL, Brigham E, Dineen R, et al. The feasibility of an air purifier and secondhand smoke education intervention in homes of inner city pregnant women and infants living with a smoker. Environ Res. 2018;160:524-530. doi:10.1016/j.envres.2017.10.020

Gu J, Uhde E, Wensing M, Xia F, Salthammer T. Emission control of desktop 3d printing: the effects of a filter cover and an air purifier. Environ Sci Technol Lett. 2019;6(8):499-503. doi:10.1021/acs.estlett.9b00376

Kim, S. Practical scale evaluation of a photocatalytic air purifier equipped with a Titania-zeolite composite bead filter for VOC removal and viral inactivation. Environmental Research. 2022;204:112036. doi:10.1016/j.envres.2021.112036

U.S. Environmental Protection Agency (EPA). What is radon gas? Is it dangerous?.

Thank you, {{form.email}}, for signing up.

There was an error. Please try again.