Intervention
Air filtration and air purifiers
Also: HEPA, air purifier, air cleaner
Removing particles from air by passing it through a filter — in the ventilation system or in a portable air purifier. HEPA filters capture over 99.97 % of particles at 0.3 micrometres; activated carbon adds some removal of gases.
Why it matters indoors
Filtration is the main defence against particulate matter that ventilation cannot remove — outdoor particles infiltrating on polluted days, and indoor particles from cooking or smoking. Portable HEPA purifiers sized to the room (clean air delivery rate matched to room volume) reduce PM₂.₅ by half or more in intervention studies, with measurable improvements in blood pressure, inflammatory markers and asthma symptoms. They do little for gases unless they carry a substantial activated-carbon stage, and nothing for CO₂ or humidity. Devices that generate ozone or ions are not recommended.
What the studies report
12 of 26 Findings — those with the strongest study design.
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| Particulate matter (PM₂.₅ and PM₁₀) | the sentence is the abstract's conclusion; the review's own meta-analysis covers seven homogeneous studies and its text layer is garbled on page 6 | — | systematic review of 47 studies with meta-analysis of seven homogeneous studies on the effectiveness of filters for particulate matter | F-0121 Effectiveness of particulate matter filtration: systematic r… (2026) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | SMD -2.27 (-2.98–-1.55) | — · home | systematic review and meta-analysis of 27 randomised controlled trials of personal-level protective measures against air pollution (air purifiers, respirators and similar), GRADE-assessed | F-0235 Effectiveness of Personal‑Level Protective Measures Against … (2026) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | SMD -3.87 (-4.59–-3.16) | — · home | systematic review and meta-analysis of 27 randomised controlled trials of personal-level protective measures against air pollution (air purifiers, respirators and similar), GRADE-assessed | F-0236 Effectiveness of Personal‑Level Protective Measures Against … (2026) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | SMD 0.04 (-0.07–0.15) · borderline | — | systematic review and meta-analysis of 27 randomised controlled trials of personal-level protective measures against air pollution (air purifiers, respirators and similar), GRADE-assessed | F-0237 Effectiveness of Personal‑Level Protective Measures Against … (2026) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | SMD -0.16 (-0.28–-0.04) | — | systematic review and meta-analysis of 27 randomised controlled trials of personal-level protective measures against air pollution (air purifiers, respirators and similar), GRADE-assessed | F-0238 Effectiveness of Personal‑Level Protective Measures Against … (2026) | machine |
| Airborne bacteria | difference 113.13 (-197.89–-28.38) | — · hospital room | systematic review and meta-analysis of indoor bioaerosols in hospital rooms: culturable bacteria and fungi compared between rooms without a heating, ventilation and air conditioning system, rooms with a conventional system and rooms with an enhanced system, pooled with random-effects models and assessed with the Agency for Healthcare Research and Quality checklist | F-1405 Dai et al. A systematic review and meta-analysis of indoor bioaerosols … (2021) | machine |
| Airborne fungi | difference 6.53 (-10.50–-2.55) | — · hospital room | systematic review and meta-analysis of indoor bioaerosols in hospital rooms: culturable bacteria and fungi compared between rooms without a heating, ventilation and air conditioning system, rooms with a conventional system and rooms with an enhanced system, pooled with random-effects models and assessed with the Agency for Healthcare Research and Quality checklist | F-1406 Dai et al. A systematic review and meta-analysis of indoor bioaerosols … (2021) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | SMD 2.27 (-2.98–-1.55) | — · home | systematic review and meta-analysis of 27 randomised controlled trials of personal-level protective measures against household air pollution: indoor particulate matter and lung function pooled as standardised mean differences with GRADE certainty | F-1511 Effectiveness of Personal‑Level Protective Measures Against … (2026) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | SMD 3.87 (-4.59–-3.16) | — · home | systematic review and meta-analysis of 27 randomised controlled trials of personal-level protective measures against household air pollution: indoor particulate matter and lung function pooled as standardised mean differences with GRADE certainty | F-1512 Effectiveness of Personal‑Level Protective Measures Against … (2026) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | other 43 | — · home | crossover randomised intervention in the homes of asthmatic children aged 6 to 12: portable air filtration switched on and off over seven weeks, with indoor fine particles measured continuously and peak expiratory flow rate recorded by the children | F-1612 Kim et al. Association between Peak Expiratory Flow Rate and Exposure L… (2020) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | difference 39.9 | — · classroom | block randomised crossover trial in elementary school classrooms: 99 classrooms with HEPA filter air cleaners compared with 87 classrooms with non-HEPA air cleaners over a school year, with classroom particle concentrations monitored throughout | F-1661 Simona Classroom air quality in a randomized crossover trial with p… (2025) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | the study found no statistically significant effect of the filtration on microvascular or lung function or on the systemic inflammation markers | — · home | crossover filtration study in the homes of elderly subjects: custom-built particle filter units run in the living room and the bedroom, with fine particles and particle number measured and cardiovascular and lung outcomes recorded before and during each exposure scenario | F-1667 An indoor air filtration study in homes of elderly: cardiova… (2013) | machine |
Each row is one Finding — a sentence as printed in one study, recorded with its page in the Coridum Knowledge Base. Follow the Finding number for the exact wording and the citation. Checked says who verified the row: machine means every automatic check passed and the surrounding text was read; person means someone read the sentence in the document. Rows are re-checked by a person over time. The studies are curated in the Coridum Knowledge Base; the reading of them together is a Claim, shown separately.
How strong is the evidence
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A single intervention study suggests that using an air purifier at home for 24 weeks reduces the severity of atopic dermatitis in children.
A Claim is Coridum reading the Findings together, not a quotation from one study — according to Coridum. The grade follows the study designs behind it: A is the strongest, D means a single study or a mechanism.
In the literature
- Indoor-air purification by photoelectrochemical oxidation mitigates allergic airway…. doi:10.1038/s41598-023-38155-0 CKB 0850
- Green et al. Demonstrating the most effective interventions to improve classroom air quality. What novel in situ tests of real-world conditions show is still missing in our guidance (2023). doi:10.1088/2752-5309/ace5c9 CKB 0820
- Design and Development of a Low-Cost IoT-Based Smart Air Cleaner for Real-Time Indoor Air… (2026). doi:10.54552/v87i3.341 CKB 1031
Studies in the Coridum Knowledge Base in which this term is used. The definition follows standard usage in WHO, ISO and textbook sources; it is not quoted from these papers.
CKB = document number in the Coridum Knowledge Base, our curated library of peer-reviewed studies. Follow the DOI for the original paper.
Cite this page
Coridum Research. Air filtration and air purifiers. Coridum Knowledge G-0068, 16 September 2026. https://coridum.com/k/G-0068/