--- topic: "Indoor Air Quality" title: "Do Air Purifiers Actually Improve Health?" order: 3 description: "Trials show air purifiers cut indoor particles and nudge blood pressure down, with mixed asthma and sleep results. Which types to avoid, and how to size one." question: "Do air purifiers actually improve health, and which types should you avoid?" answer: "Purifiers reliably cut indoor particles and likely lower blood pressure slightly; asthma and sleep benefits are mixed, and ozone-emitting types should be avoided." actions: - "Size the unit by CADR: aim for about two-thirds of the floor area in square feet (about 195 for a 300 ft² room) and run it faster when home [1]." - "Choose a true-HEPA unit that makes no ozone: avoid ozone generators, and check that ionizer, plasma or electrostatic models are on the CARB or AHAM low-ozone lists [1][2]." - "Treat a purifier as a supplement, not a fix: remove sources first (no smoking indoors) and ventilate with clean outdoor air [1]." cautions: - "If you or your child has asthma, keep your prescribed controller plan. Purifiers lowered unscheduled visits in one trial but did not significantly reduce symptoms in two others [3][4][5]." - "Ozone-emitting devices irritate the lungs and may worsen asthma, so do not run them in rooms where people or pets stay [2]." - "A purifier is not a blood-pressure treatment: pooled effects were only a few mm Hg, so keep taking prescribed medicine [6]." confidence: 3 confidenceNote: "Seven small-to-moderate randomized trials and one meta-analysis agree purifiers cut particles and nudge blood pressure, but asthma and sleep results conflict or come from pilots." evidenceSummary: rctCount: 7 observationalCount: 0 metaAnalysisCount: 1 totalParticipants: "900+ in individual trials; the blood pressure meta-analysis pooled about 880" replicated: true newestStudyYear: 2026 references: - id: "1" url: "https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home" title: "Guide to Air Cleaners in the Home" authors: "U.S. Environmental Protection Agency" year: 2026 journal: "EPA" - id: "2" url: "https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners" title: "Ozone Generators that are Sold as Air Cleaners" authors: "U.S. Environmental Protection Agency" year: 2026 journal: "EPA" - id: "3" pmid: "21149427" title: "Effects of HEPA air cleaners on unscheduled asthma visits and asthma symptoms for children exposed to secondhand tobacco smoke" authors: "Lanphear BP, Hornung RW, Khoury J, et al." year: 2011 journal: "Pediatrics" - id: "4" pmid: "34547084" title: "Effect of School Integrated Pest Management or Classroom Air Filter Purifiers on Asthma Symptoms in Students With Active Asthma: A Randomized Clinical Trial" authors: "Phipatanakul W, Koutrakis P, Coull BA, et al." year: 2021 journal: "JAMA" - id: "5" pmid: "40617376" title: "AIRWEIGHS: A Randomized Controlled Trial of Air Cleaners in Normal Weight and Overweight/Obese Children With Asthma" authors: "Qiu AY, Brigham EP, Woo H, et al." year: 2025 journal: "J Allergy Clin Immunol Pract" - id: "6" pmid: "37421892" title: "An updated systematic review and meta-analysis on portable air cleaners and blood pressure: Recommendations for users and manufacturers" authors: "Faridi S, Allen RW, Brook RD, et al." year: 2023 journal: "Ecotoxicol Environ Saf" - id: "7" pmid: "26022815" title: "Cardiopulmonary benefits of reducing indoor particles of outdoor origin: a randomized, double-blind crossover trial of air purifiers" authors: "Chen R, Zhao A, Chen H, et al." year: 2015 journal: "J Am Coll Cardiol" - id: "8" pmid: "30208394" title: "Effect of Portable Air Filtration Systems on Personal Exposure to Fine Particulate Matter and Blood Pressure Among Residents in a Low-Income Senior Facility: A Randomized Clinical Trial" authors: "Morishita M, Adar SD, D'Souza J, et al." year: 2018 journal: "JAMA Intern Med" - id: "9" pmid: "36351665" title: "Can air purification improve sleep quality? A 2-week randomised-controlled crossover pilot study in healthy adults" authors: "Lamport DJ, Breese E, Gião MS, et al." year: 2023 journal: "J Sleep Res" - id: "10" pmid: "38388489" title: "Improved childhood asthma control after exposure reduction interventions for desert dust and anthropogenic air pollution: the MEDEA randomised controlled trial" authors: "Kouis P, Galanakis E, Michaelidou E, et al." year: 2024 journal: "Thorax" - id: "11" pmid: "16268833" title: "Effects of an ozone-generating air purifier on indoor secondary particles in three residential dwellings" authors: "Hubbard HF, Coleman BK, Sarwar G, et al." year: 2005 journal: "Indoor Air" - id: "12" pmid: "21118308" title: "The effect of an ion generator on indoor air quality in a residential room" authors: "Waring MS, Siegel JA" year: 2011 journal: "Indoor Air" --- Yes, modestly. In trials, purifiers cut indoor fine particles by roughly 60% and lowered systolic blood pressure by a few points [6][7][8]. Benefits for asthma and sleep are mixed, with some trials positive and others null [3][4][5][9]. Pick a true-HEPA unit sized to the room, and avoid any device that makes ozone, including some ionizers and plasma cleaners [1][2]. ## How it works This page covers what purifiers do for health. For how HEPA and carbon filters work, see [Air Purifiers, Filters, and Ventilation](/air-quality/air-purifiers-and-filters). For smoke and cooking sources, see [Protecting Yourself from Wildfire Smoke](/wildfire-smoke/protecting-yourself-from-wildfire-smoke) and [Are Gas Stoves Bad for Your Health?](/gas-stoves/are-gas-stoves-bad-for-your-health). **Particles drop, but health effects are small.** Across blood-pressure trials, purifiers removed about 60% of indoor PM2.5 on average, with a range of 23% to 82% [6]. **Blood pressure.** A pooled analysis of 17 true-versus-sham trials found systolic pressure 2.35 mm Hg lower, and 3.62 mm Hg lower once high-risk-of-bias studies were removed [6]. In older adults in Detroit, three days of filtration lowered systolic pressure by 3.2 mm Hg [8]. In Shanghai students, a 57% particle cut over 48 hours lowered blood pressure and several inflammatory markers [7]. **Asthma.** Results conflict. HEPA cleaners cut unscheduled asthma visits in children exposed to secondhand smoke [3], and a package of alerts plus HEPA at home and school improved asthma control in a dust-storm region [10]. But classroom HEPA filters did not significantly reduce symptom-days [4], and home cleaners that cut PM2.5 by 64% did not improve asthma outcomes [5]. **Sleep.** A small two-week crossover pilot found about 12 more minutes of sleep a night, but more time awake after falling asleep [9]. **Choose by CADR.** The clean air delivery rate (CADR) rates particle removal per minute. The EPA's sizing chart works out to a CADR of about two-thirds of the room's floor area, such as 195 for a 300 ft² room with 8-foot ceilings [1]. Higher fan speeds and longer run times filter more air [1]. CADR does not rate gas removal [1]. **Types to avoid.** Ozone generators deliberately make ozone, a lung irritant. They can exceed health standards even when used as directed, and they do not remove particles [2]. Electrostatic precipitators, ionizers, some UV units, and plasma cleaners may also emit ozone [1]. In real homes, an ozone generator near a pine-oil cleaner raised fine particles [11], and an ion generator raised ozone and, near an air freshener, ultrafine particles [12]. ## The evidence in detail **Blood pressure trials.** Chen and colleagues ran a randomized, double-blind crossover trial in 35 healthy Shanghai students who alternated true and sham purifiers for 48 hours with a two-week washout [7]. True purification cut PM2.5 by 57% (96.2 to 41.3 µg/m³) and lowered systolic pressure by 2.7%, diastolic by 4.8%, and exhaled nitric oxide by 17%, along with interleukin-1β (68%) and myeloperoxidase (33%) [7]. Lung-function gains were not significant [7]. Morishita and colleagues studied 40 older adults in a Detroit senior building across three 3-day exposures: sham, low-efficiency HEPA-type, and true HEPA [8]. Personal PM2.5 fell from 15.5 to 10.9 and 7.4 µg/m³ [8]. Any filtration lowered systolic pressure by 3.2 mm Hg (95% CI -6.1 to -0.2) and diastolic by 1.5 mm Hg (-3.3 to 0.2); most secondary outcomes did not improve, and the true-HEPA effect alone (-2.9, -6.2 to 0.5) was not significant [8]. Faridi and colleagues pooled 17 trials with about 880 participants: -2.35 mm Hg systolic (-4.5 to -0.2) and -0.81 diastolic (-1.86 to 0.24) [6]. Apart from the Chinese studies, trials were in low-pollution settings [6]. **Asthma trials.** Lanphear and colleagues randomized 225 children aged 6 to 12 with asthma who lived with smokers to active or inactive HEPA cleaners [3]. The active group had 42 fewer unscheduled asthma visits (P = .043), but parent-reported symptoms, exhaled nitric oxide, air nicotine, and cotinine did not differ [3]. In the School Inner-City Asthma Intervention Study, 236 students in 41 schools were randomized to classroom HEPA or sham filters [4]. Symptom-days per two weeks were 1.6 versus 1.8 (incidence rate ratio 1.47, 95% CI 0.79 to 2.75), a null result; a school pest-management arm was also null [4]. The MEDEA trial randomized 182 children in Cyprus and Greece to no intervention, alerts plus advice to stay indoors, or that plus HEPA purifiers at home and school [10]. After three months, the combined arm improved on the childhood Asthma Control Test by 2.63 points (0.72 to 4.54) and FEV1 by 4.26 percentage points (0.54 to 7.99) versus controls [10]. The package cannot separate the filter from the advice. AIRWEIGHS randomized 164 children to HEPA or filterless units: PM2.5 fell 64.4%, yet there was no improvement in primary or secondary asthma outcomes at 12 weeks [5]. **Sleep.** Lamport and colleagues tested 30 healthy adults in a double-blind crossover, two weeks per condition [9]. The HEPA filter increased total sleep time by about 12 minutes and time in bed by 19 minutes a night, but wake time after sleep onset was higher, and many outcomes did not change [9]. **Ozone-producing devices.** Hubbard and colleagues released terpenes from a pine-oil cleaner in three homes while an ozone generator ran; particle number and mass rose when both were present [11]. Waring and Siegel tested an ion generator in a 27 m³ room: ozone rose in every configuration, formaldehyde and nonanal rose (within uncertainty in some cases), and ultrafine particles rose with an air freshener present; they advised limiting ion-generator use [12]. The EPA states that ozone can cause chest pain, cough, and shortness of breath and may worsen asthma [2]. **Null and conflicting results.** Two of the four asthma trials were null [4][5], and the positive ones paired filters with other measures or changed visits more than symptoms [3][10]. The investigators of the school trial noted that baseline allergen, particle, and symptom levels may matter [4]. The blood pressure effect is small and was not significant in some single comparisons [8], though it grew when biased studies were removed [6]. None of these trials lasted long enough to show whether purifiers prevent heart attacks or new asthma. **Bottom line (confidence 3 of 5).** Purifiers reliably remove particles and probably lower blood pressure by a few mm Hg. For asthma and sleep the evidence is mixed. Avoid ozone-emitting designs.