What does an air purifier do? Your complete guide

An air purifier is a device that removes harmful particles, allergens, and pollutants from indoor air using advanced filtration technology. Modern air purifiers can eliminate up to 99.97% of airborne contaminants as small as 0.3 micrometers, including dust, pollen, pet dander, smoke, bacteria, and even some viruses.

But here's what might surprise you: the air inside your home can actually be more polluted than outdoor air. From pet dander to dust mites, cooking fumes to cleaning product chemicals, even a spotless home harbors invisible airborne contaminants that can irritate your lungs and worsen allergies.

These invisible particles can irritate your lungs and worsen allergies, even when your home looks perfectly clean.

Indoor air quality is even more important to consider as we spend a tremendous amount of time indoors. The average American spends 85-90% of their time inside.

The people most susceptible to air pollution (the elderly and those with cardiovascular or respiratory problems) often spend even more time indoors than average. This makes protecting indoor air quality crucial for the most vulnerable.

Some indoor air pollutants have actually increased in recent decades. Energy-efficient buildings insulate better but provide less fresh air circulation. Meanwhile, we're using more synthetic materials in buildings, furniture, and personal care products that release VOCs.

Climate change has also escalated the problem, causing more frequent wildfires that degrade both outdoor and indoor air quality.

The good news? Air purifiers give you real control over the air you breathe at home.

What is an air purifier and what does it do?

An air purifier is a relatively simple device made up of two main components: a fan and a filter.

Here's how they work together: The fan draws in air from your room and pushes it through one or more filters. These filters trap airborne particles and gases. Then the purifier sends the cleaned air back into your room.

How do air purifiers work? The science explained.

A typical air purifier uses one or more specially designed filters to capture airborne contaminants called particulate matter (PM). These particles are incredibly small, far smaller than anything visible to the naked eye.

Dust, pollen, and mold are classified as PM10, meaning they have diameters smaller than 10 micrometers. These are the larger particles that air purifiers target.

Smoke, heavy metals, bacteria, and viruses fall under PM2.5, having diameters smaller than 2.5 micrometers. These particles are considered more dangerous than PM10 because they're small enough to penetrate deep into the lungs and enter the bloodstream.

Ultra-fine dust and some viruses, including COVID-19, are even smaller at PM0.3 or less. These are the tiniest, most dangerous particles that only the best filters can capture.

Air purifiers use advanced filters made of mesh material designed to capture these microscopic particles. Basic filters catch PM10 and larger particles like dust and pollen. Higher-efficiency filters are thicker and have finer mesh, which can capture much smaller particles, including smoke, bacteria, and viruses.

Understanding HEPA filters: The gold standard

The gold standard is the HEPA (High Efficiency Particulate Air) filter. To earn HEPA certification, filters must trap 99.97% of particles as small as 0.3 micrometers.

This means HEPA filters capture nearly everything harmful: allergens, smoke, bacteria, mold spores, and even some viruses. It's why HEPA is the filter type experts recommend for anyone serious about air quality.

HEPA filters capture air particles through three mechanisms: interception, impaction, and diffusion.

• Interception occurs when particles stick to the filter fibers as air flows past.
• Impaction happens when larger particles can't navigate around fibers and embed themselves directly into the material.
• Diffusion is the most fascinating mechanism. Ultra-small particles (smaller than 0.1 microns) bounce around randomly as they move through the filter. This zigzag motion slows them down until they're captured through interception or impaction.

HEPA filters become less effective the longer they're used, which is why they need replacement every 6-12 months. Saturated filters can't trap new particles efficiently and may even release trapped contaminants back into your air.

This is where pre-filters come in. These capture larger dust particles and hair before air reaches the HEPA filter, extending the HEPA's lifespan and saving you money on replacements.

How air purifiers remove odors and VOCs

HEPA filters are powerful against particles, but most gases pass right through them. This includes odors from cooking, pets, smoke, and volatile organic compounds (VOCs) from furniture and cleaning products.

That's why many quality air purifiers include an activated carbon filter. These filters specifically target gases and odors that HEPA can't capture.

Activated carbon is a highly porous form of carbon covered in millions of microscopic holes that trap gases. The surface area is astounding: each gram can have over 1,000 square meters of surface area.

To put that in perspective, a single gram of activated carbon has roughly the surface area of two basketball courts. All that surface area packed into a tiny space is what makes it so effective at capturing odors.

Activated carbon works through adsorption, a process where gas molecules stick to the carbon's surface. Since odors are simply chemicals in gas form, they get trapped in the carbon's microscopic pores.

Think of it like a sponge soaking up water. Eventually, the activated carbon becomes saturated and can't absorb any more. Once saturated, it needs replacement or your purifier will stop removing odors effectively.

How often? Most carbon filters need replacement every 3-6 months, depending on how much pollution they're filtering.

Types of air purifier filters compared

Different filters target different contaminants. Here's what each type does:

Bottom line: Look for air purifiers with true HEPA filters. Activated carbon is a valuable add-on if you're concerned about odors or VOCs.

Air purifier benefits: What the science says

Air purifiers are backed by substantial scientific research. Dozens of peer-reviewed studies have documented their effectiveness at removing particulates and improving health outcomes.

Here's what the science actually shows:

• 🫁 Asthma: A 2011 study found that smoke-exposed asthmatic children required significantly fewer unplanned doctors visits when HEPA air purifiers were used in the home.
• 🤧 Allergies: A 2020 study on adults with allergic rhinitis found that using HEPA air purifiers led to significantly reduced medication use and lower levels of allergens.
• 🫀 Blood pressure: A 2025 study of adults living near highways with elevated systolic blood pressure (SBP) found that one month of running HEPA air purifiers led to a significantly lower SBP.
• 🫁 COPD: A 2022 study of adults with chronic obstructive pulmonary disease (COPD) found that adding HEPA air purifiers in the home resulted in better respiratory symptom scores and overall well-being.
• 🤒 Respiratory infections: A 2024 study found that running HEPA air purifiers in secondary school classrooms removed 77% of fine particulate matter and was associated with a drop in respiratory infection absences and coughing in the classroom.
• 🔥 Wildfire smoke: A 2022 government report concluded that HEPA air purifiers can effectively reduce concentrations of indoor PM2.5 and lower the negative health risks of wildfire smoke exposure.

What to expect: Real-world air purifier performance

Lab tests show impressive numbers, but here's what air purifiers actually deliver in everyday use:

Particle reduction:

• HEPA air purifiers typically reduce indoor PM2.5 levels by 50-90%
• Results vary based on outdoor air quality, room size, and how often you run the unit
• Maximum effectiveness requires running continuously or at least 12-18 hours daily

Timeline for results:

• Immediate (30 mins - 2 hours): Noticeable air quality improvement on monitors
• Few days: Reduced allergy symptoms for many users
• 1-2 weeks: Noticeable reduction in dust accumulation
• 2-4 weeks: Improved sleep quality and respiratory comfort (for those with sensitivities)

What air purifiers can't do:

• Eliminate surface dust (still need to clean regularly)
• Remove the source of mold, though they can trap airborne spores
• Make up for poor ventilation
• Filter 100% of ultra-fine particles smaller than 0.1 micrometers

The takeaway? Air purifiers work well, but they're one tool in a comprehensive approach to indoor air quality.

What to look for when buying an air purifier

Air purifiers are incredibly impactful devices, but their effectiveness depends on several factors. Room size, filter types, clean air delivery rate (CADR) ratings, and your specific air quality concerns all matter when choosing the right model.

The problem? Marketing claims often exaggerate what air purifiers can actually do. An air purifier might be advertised for large living areas but only do one air change per hour (ACH). That's far below the recommended 3-5 ACH needed to effectively clean the air.

Without understanding these specifications, you could end up with an underpowered purifier that doesn't solve your air quality problems. Or you might overspend on features you don't actually need.

We all deserve to breathe clean air, but finding the right air purifier shouldn't be overwhelming.

That's exactly why we created Find My Purifier, a free tool that cuts through the marketing hype and matches you with air purifiers suited to your specific situation. Answer 10 quick questions about your room size, air quality concerns, and preferences, and get personalized recommendations.

Take the quiz now → It takes less than 2 minutes, and no email is required.

💨 Air purifier FAQs: Your questions answered

Do air purifiers really work?

Yes, scientific research consistently shows that HEPA air purifiers effectively reduce airborne particulate matter by 50-90% in real-world settings. Studies have demonstrated measurable health benefits including reduced asthma symptoms, fewer allergy medication needs, improved blood pressure in polluted areas, and decreased respiratory infections.

However, effectiveness depends on proper sizing for your room, running the purifier consistently, and regular filter replacement. Our quiz can help you find an appropriately-sized purifier for your space.

What do air purifiers help with?

Air purifiers with HEPA filters help with:

• Seasonal and year-round allergies (pollen, dust mites, mold)
• Asthma symptoms and respiratory issues
• Pet dander and pet odors (with carbon filter)
• Wildfire and cigarette smoke
• Cooking odors (with carbon filter)
• Dust reduction
• Bacteria and some viruses
• VOCs from furniture, paint, and cleaning products (with carbon filter)

How long does it take for an air purifier to work?

Most air purifiers can noticeably improve air quality within 30 minutes to 2 hours, depending on the room size and the purifier's CADR rating. For optimal results, run your air purifier continuously or at least 12-18 hours per day. You may notice reduced allergy symptoms within a few days of consistent use.

Where should I place an air purifier?

For maximum effectiveness, place your air purifier:

• In the room where you spend the most time (bedroom or living room)
• At least 6-12 inches away from walls for proper airflow
• Away from corners and behind furniture
• Near the source of pollution when possible (but not mandatory)

Many people run purifiers in bedrooms at night for better sleep quality and reduced nighttime allergy symptoms.

How often do I need to replace air purifier filters?

Filter replacement schedule:

• Pre-filters: Every 1-3 months (some are washable)
• HEPA filters: Every 6-12 months for most residential use
• Activated carbon filters: Every 3-6 months

Most air purifiers have filter replacement indicators. Running a purifier with old filters significantly reduces effectiveness and may even release trapped particles back into your air.

Are air purifiers worth it?

Air purifiers are worth the investment if you:

• Have allergies or asthma
• Live with pets
• Live in an area with wildfire smoke or high outdoor pollution
• Have respiratory sensitivities
• Want to reduce household dust
• Are concerned about indoor air quality

The upfront cost ($100-$800) plus ongoing filter costs ($50-$150/year) are generally worthwhile given the documented health benefits and quality of life improvements.

Can air purifiers remove COVID-19?

HEPA filters can capture particles as small as 0.3 micrometers, which includes the size range of respiratory droplets that carry COVID-19. While air purifiers can reduce airborne virus particles, they're not a complete solution. Combine air purifiers with other protective measures like vaccination, masking, ventilation, and surface cleaning for comprehensive protection.

Do air purifiers use a lot of electricity?

Most air purifiers use 30-200 watts on high speed, costing approximately $15-$50 per year in electricity if run 24/7. This is similar to running a computer monitor or laptop. Many models have eco modes or auto settings that reduce energy consumption while maintaining air quality.

Is an air purifier the same as a humidifier?

No, an air purifier is designed to improve indoor air quality by removing pollutants with advanced filters. Humidifiers work by adding moisture to the air, but they do not remove harmful particulate matter.

Is an air purifier the same as a dehumidifier?

No, a dehumidifier simply removes moisture from the air. An air purifier actually cleans the air by trapping airborne contaminants in its filters.

Do you need an air purifier if you have a central air filter?

Central air filters are designed primarily to protect your home's heating and cooling system, not your indoor air. They use basic filters that miss smaller particles.

In fact, central air systems can actually circulate particulate matter throughout your home. Pet dander, viruses, bacteria, and allergens get pushed through your ducts into every room, exposing you repeatedly.

Air purifiers differ in two key ways. First, they use much finer filters (like HEPA) that capture the tiny, lung-irritating particles central air filters miss. Second, they're designed to thoroughly clean the air in a single room with multiple air changes per hour, not just push air around your house.

Do air purifiers help with mold?

Yes, air purifiers can effectively remove mold spores from the air. This prevents you from breathing them in and reduces their spread to other areas.

However, air purifiers can't eliminate the source of mold growth. To truly solve a mold problem, you need to address the root cause: fix water leaks, improve ventilation, reduce humidity, and clean affected surfaces.

Think of it this way: an air purifier treats the symptom (airborne spores) while moisture control treats the disease (mold growth).

Do air purifiers help with dust?

Air purifiers can help trap ultra-fine dust particles from the air. Many people report noticing less dust accumulation on surfaces when running a purifier consistently.

Here's the catch: larger dust particles are often too heavy to stay airborne long enough to reach your purifier. They settle on surfaces before the purifier can capture them.

For best results with dust, combine strategies. Run an air purifier for fine airborne dust, and vacuum regularly (ideally with a HEPA-filter vacuum) to capture the heavier particles that settle.

Do air purifiers help with smells?

Only air purifiers with an activated carbon filter can effectively tackle smells. HEPA filters capture particles, but odors are gases, and gases pass right through HEPA.

Activated carbon filters work differently by adsorbing odor molecules onto their surface. If eliminating pet odors, cooking smells, or cigarette smoke is a priority for you, make sure any air purifier you're considering includes activated carbon.

About this guide

This guide was created by the team at Find My Purifier, a resource dedicated to helping people navigate the complex world of indoor air quality solutions. Our content is based on peer-reviewed research, EPA guidelines, and real-world testing data. We regularly update our guides to reflect the latest air quality science and product innovations.

Last Updated: November 5, 2025

References

Albers, K. (2024, May 3). What Is a HEPA Filter and How Does a HEPA Filter Work?. ISO-Aire. https://www-iso--aire-com.translate.goog/blog/what-is-a-hepa-filter-and-how-does-it-work?

Banholzer, N., Jent, P., Bittel, P., Zürcher, K., Furrer, L., Bertschinger, S., Weingartner, E., Ramette, A., Egger, M., Hascher, T., & Fenner, L. (2024). Air Cleaners and respiratory infections in schools: A modeling study based on epidemiologic, environmental, and Molecular Data. Open Forum Infectious Diseases, 11(4). https://doi.org/10.1093/ofid/ofae169

Baugh, T. (2020, August 12). Do Air Purifiers Work? Your Guide To How Do Air Purifiers Work. Carrier. https://www.carrier.com/residential/en/us/products/indoor-air-quality/air-purifiers/do-air-purifiers-work/

Bonan, J., Granella, F., Renna, S., Sarmiento, L., & Tavoni, M. (2025, June). The Effect of Air Purifiers in Schools. RFF. https://media.rff.org/documents/WP_25-17.pdf

Booth, T. (2025, April 28). A jargon-free guide to air purifiers. HouseFresh. https://housefresh.com/what-does-an-air-purifier-do/

Chen, C., & Zhao, B. (2011). Review of relationship between indoor and outdoor particles: I/O ratio, infiltration factor and penetration factor. Atmospheric Environment, 45(2), 275–288. https://doi.org/10.1016/j.atmosenv.2010.09.048

Cherney, K., & Lamoreux, K. (2025, March 24). Do Air Purifiers Actually Work?. Healthline. https://www.healthline.com/health/allergies/do-air-purifiers-work

Ebrahimifakhar, A., Poursadegh, M., Hu, Y., Yuill, D. P., & Luo, Y. (2024). A systematic review and meta-analysis of field studies of Portable Air Cleaners: Performance, User Behavior, and by-product emissions. Science of The Total Environment, 912, 168786. https://doi.org/10.1016/j.scitotenv.2023.168786

Environmental Protection Agency. (2025a, June 15). Indoor Air Quality. EPA. https://www.epa.gov/report-environment/indoor-air-quality

Environmental Protection Agency. (2025b, August 25). Indoor Particulate Matter. EPA. https://www.epa.gov/indoor-air-quality-iaq/indoor-particulate-matter

Francis, H., Fletcher, G., Anthony, C., Pickering, C., Oldham, L., Hadley, E., Custovic, A., & Niven, R. (2003). Clinical effects of air filters in homes of asthmatic adults sensitized and exposed to pet allergens. Clinical & Experimental Allergy, 33(1), 101–105. https://doi.org/10.1046/j.1365-2222.2003.01570.x

International Enviroguard. (2022, March 31). What Is PM0.3 and Why Does It Matter?  . International Enviroguard. https://int-enviroguard.com/blog/what-is-pmo-and-why-does-it-matter/

Joseph, G., Schramm, P., Vaidyanathan, A., Breysse, P., & Goodwin, B. (2020, July). Evidence on the Use of Indoor Air Filtration as an Intervention for Wildfire Smoke Pollutant Exposure. Centers for Disease Control. https://www.cdc.gov/air-quality/media/Wildfire-Air-Filtration-508.pdf

KLEPEIS, N. E., NELSON, W. C., OTT, W. R., ROBINSON, J. P., TSANG, A. M., SWITZER, P., BEHAR, J. V., HERN, S. C., & ENGELMANN, W. H. (2001). The National Human Activity Pattern Survey (NHAPS): A Resource for assessing exposure to environmental pollutants. Journal of Exposure Science & Environmental Epidemiology, 11(3), 231–252. https://doi.org/10.1038/sj.jea.7500165

Lanphear, B., Hornung, R., Khoury, J., Yolton, K., Lierl, M., & Kalkbrenner, A. (2010). Effects of HEPA air cleaners on unscheduled asthma visits and asthma symptoms for children exposed to secondhand tobacco smoke. PEDIATRICS, 127(2). https://doi.org/10.1542/peds.2009-2312d

Lu, F., Laumbach, R. J., Legard, A., Myers, N., Black, K., Ohman-Strickland, P., Alimokhtari, S., de Resende, A., Calderón, L., Mainelis, G., & Kipen, H. (2023). Real-World Effectiveness of Portable Air Cleaners in Reducing Home Particulate Matter Concentrations. https://doi.org/10.2139/ssrn.4377290

Park, K. H., Sim, D. W., Lee, S. C., Moon, S., Choe, E., Shin, H., Kim, S. R., Lee, J.-H., Park, H. H., Huh, D., & Park, J.-W. (2020). Effects of air purifiers on patients with allergic rhinitis: A multicenter, randomized, double-blind, and placebo-controlled study. Yonsei Medical Journal, 61(8), 689. https://doi.org/10.3349/ymj.2020.61.8.689

Puragen. (2025, October 7). What is Activated Carbon?. Puragen. https://puragen.com/us/resources/what-is-activated-carbon/

Thomas & Galbraith. (2023, January 4). This Is Why You Need to Change Your Furnace Filter. Thomas & Galbraith. https://thomasgalbraith.com/knowledge-center/changing-furnace-filters/

Walther, O. (2025, August 6). Air Purifiers May Reduce Heart Risks for People Exposed to Traffic Pollution. American College of Cardiology. https://www.acc.org/About-ACC/Press-Releases/2025/08/06/15/32/Air-Purifiers-May-Reduce-Heart-Risks-for-People-Exposed-to-Traffic-Pollution

Wasserman, H. (2022, December 5). Household Air Cleaners Improve Heart Health Among Individuals with COPD, Researchers Find. Johns Hopkins Medicine. https://www.hopkinsmedicine.org/news/newsroom/news-releases/2022/12/household-air-cleaners-improve-heart-health-among-individuals-with-copd-researchers-find