Indoor environment factor · measured in µg/m³
Particulate matter (PM₂.₅ and PM₁₀)
Also: PM2.5, PM10, fine particles, fine particulate matter
Airborne particles small enough to stay suspended and be inhaled: PM₁₀ is 10 micrometres or less in diameter, PM₂.₅ is 2.5 micrometres or less. The smaller the particle, the deeper it travels into the lungs — and, for the finest fractions, into the bloodstream.
“Nearly all the classrooms in Athi River schools had PM2.5 and PM10 median levels that exceeded the World Health Organization (WHO) recommended levels.”
Why it matters indoors
Particulate matter is the mixture of solid and liquid particles suspended in air — dust, soot, smoke, pollen, droplets and the secondary particles formed when gases react. It is classified by size because size decides where in the body a particle ends up: PM₁₀ is mostly stopped in the nose and upper airways, PM₂.₅ reaches the small airways and alveoli, and ultrafine particles below 0.1 micrometres can pass into the bloodstream.
Where it comes from indoors
Cooking is usually the largest indoor source in homes — frying, grilling and gas burners release fine particles in bursts that can exceed outdoor levels tenfold for half an hour. Candles, incense, fireplaces and tobacco add combustion particles. Resuspension from carpets and soft furnishings, laser printers and cleaning sprays contribute in offices. The remaining share is outdoor air: traffic and heating particles enter through windows, gaps and ventilation systems without adequate filtration.
Health effects
Short-term exposure irritates the airways, worsens asthma and triggers heart-rhythm disturbances in susceptible people. Long-term exposure is linked to chronic obstructive pulmonary disease, cardiovascular disease, lung cancer and reduced life expectancy; the WHO ranks ambient particulate matter among the leading environmental risk factors for premature death. Children, older adults and people with existing heart or lung conditions are most affected.
Exposure limits
| Jurisdiction | PM₂.₅ | PM₁₀ | Averaging time | Source |
|---|---|---|---|---|
| World Health Organization (2021 guidelines) | 5 µg/m³ | 15 µg/m³ | annual | WHO AQG 2021 |
| World Health Organization (2021 guidelines) | 15 µg/m³ | 45 µg/m³ | 24 hours | WHO AQG 2021 |
| European Union (ambient air, from 2030) | 10 µg/m³ | 20 µg/m³ | annual | Directive (EU) 2024/2881 |
| European Union (ambient air, from 2030) | 25 µg/m³ | 45 µg/m³ | 24 hours | Directive (EU) 2024/2881 |
The EU values are outdoor (ambient) standards; the EU has no binding indoor limit for particulate matter. Slovak, UAE and Hong Kong indoor values are being compiled in the indoor air quality limits table.
How it is measured
Reference methods weigh particles collected on a filter. Continuous monitors — including the sensors in Coridum devices — use optical particle counters: a laser illuminates the air stream and the light scattered by each particle is converted into a size estimate, from which mass concentration is calculated. Optical sensors respond within seconds, which is what makes cooking peaks and ventilation effects visible.
What the studies report
12 of 411 Findings — those with the strongest study design.
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| Atopic dermatitis (eczema) | OR 0.96 (0.83–1.11) · borderline | young age groups (infants and children) | systematic review and meta-analysis | F-0062 Ngoc et al. Systematic Review and Meta-Analysis of Human Skin Diseases D… (2017) | machine |
| Atopic dermatitis (eczema) | OR 1.05 (0.95–1.16) · borderline | young age groups (infants and children) | systematic review and meta-analysis | F-0063 Ngoc et al. Systematic Review and Meta-Analysis of Human Skin Diseases D… (2017) | machine |
| Skin diseases | difference 1.01 (0.08–2.05) per 10 % | — | systematic review and meta-analysis | F-0064 Ngoc et al. Systematic Review and Meta-Analysis of Human Skin Diseases D… (2017) | machine |
| Skin diseases | difference 1.60 (0.45–2.82) per 10 % | — | systematic review and meta-analysis | F-0065 Ngoc et al. Systematic Review and Meta-Analysis of Human Skin Diseases D… (2017) | machine |
| Cardiovascular disease (CVD) | HR 1.13 (1.08–1.19) per 10 | — | systematic review and meta-analysis of 38 publications (35 cohort and 3 case-control studies) on long-term particulate matter exposure in low- and middle-income countries; preprint (Research Square), not peer reviewed | F-0066 The chronic effects of particulate matter (PM2.5, PM10 and P… (2022) | machine |
| Respiratory tract diseases | HR 1.10 (1.02–1.18) per 10 | — | systematic review and meta-analysis of 38 publications (35 cohort and 3 case-control studies) on long-term particulate matter exposure in low- and middle-income countries; preprint (Research Square), not peer reviewed | F-0067 The chronic effects of particulate matter (PM2.5, PM10 and P… (2022) | machine |
| Cardiovascular disease (CVD) | HR 1.17 (1.00–1.37) per 10 · borderline | — | systematic review and meta-analysis of 38 publications (35 cohort and 3 case-control studies) on long-term particulate matter exposure in low- and middle-income countries; preprint (Research Square), not peer reviewed | F-0068 The chronic effects of particulate matter (PM2.5, PM10 and P… (2022) | machine |
| Respiratory tract diseases | HR 1.28 (1.10–1.49) per 10 | — | systematic review and meta-analysis of 38 publications (35 cohort and 3 case-control studies) on long-term particulate matter exposure in low- and middle-income countries; preprint (Research Square), not peer reviewed | F-0069 The chronic effects of particulate matter (PM2.5, PM10 and P… (2022) | machine |
| Stroke | HR 1.09 (1.06–1.12) per 10 | — | systematic review and meta-analysis of 38 publications (35 cohort and 3 case-control studies) on long-term particulate matter exposure in low- and middle-income countries; preprint (Research Square), not peer reviewed | F-0070 The chronic effects of particulate matter (PM2.5, PM10 and P… (2022) | machine |
| Cardiovascular disease (CVD) | HR 1.08 (1.06–1.10) per 10 | males | systematic review and meta-analysis of 38 publications (35 cohort and 3 case-control studies) on long-term particulate matter exposure in low- and middle-income countries; preprint (Research Square), not peer reviewed | F-0071 The chronic effects of particulate matter (PM2.5, PM10 and P… (2022) | machine |
| Cardiovascular disease (CVD) | HR 1.14 (1.12–1.17) per 10 | females | systematic review and meta-analysis of 38 publications (35 cohort and 3 case-control studies) on long-term particulate matter exposure in low- and middle-income countries; preprint (Research Square), not peer reviewed | F-0072 The chronic effects of particulate matter (PM2.5, PM10 and P… (2022) | machine |
| Gestational diabetes | OR 1.06 (1.05–1.08) | pregnant women | systematic review and meta-analysis of 35 epidemiological studies (33 cohort, 1 cross-sectional, 1 case-control) covering 6,939,725 pregnant women | F-0078 Association of air pollution and fine particulate matter (PM… (2023) | 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
-
In adults, long-term exposure to fine particulate matter (PM₂.₅) is associated with newly diagnosed atopic dermatitis; a second systematic review, based on self-reported exposure and self-reported skin effects, found no association.
-
In infants with moderate atopic dermatitis, a single cohort suggests that long-term exposure to particulate matter below 10 µm (PM₁₀) makes the disease more likely to persist to the age of three; in the whole cohort no association was found.
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.
How Coridum measures it: Coridum devices use a laser optical particle counter that sizes particles as they scatter light, reporting PM₁, PM₂.₅ and PM₁₀ mass concentrations every few seconds.
Identifiers
- MeSH
- D052638
Frequently asked questions
Is PM₂.₅ more dangerous than PM₁₀?
Per microgram, yes. PM₂.₅ penetrates to the alveoli and the finest fraction crosses into the blood, which is why the WHO guideline for PM₂.₅ (5 µg/m³ annual) is three times stricter than for PM₁₀ (15 µg/m³ annual).
What produces particulate matter indoors?
Cooking (especially frying and gas hobs), candles and incense, tobacco and vaping, wood stoves and fireplaces, printers, cleaning with sprays, and outdoor air entering through windows and ventilation.
What is a safe PM₂.₅ level indoors?
There is no threshold below which effects stop. WHO recommends staying under 15 µg/m³ as a 24-hour average and 5 µg/m³ as an annual average; indoor peaks during cooking can exceed 100 µg/m³ for short periods.
Sources
- WHO global air quality guidelines: particulate matter (PM₂.₅ and PM₁₀), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. World Health Organization, 2021.
- Directive (EU) 2024/2881 of the European Parliament and of the Council on ambient air quality and cleaner air for Europe.
- Krittanawong PM2.5 and cardiovascular diseases - State-of-the-art review (2023). International journal of cardiology. Cardiovascular risk and prevention. doi:10.1016/j.ijcrp.2023.200217 CKB 0588
- Particulate matter causes skin barrier dysfunction. JCI insight. doi:10.1172/jci.insight.145185 CKB 0668
- Li Unrecognized pollution by inorganic condensable particulate matter in the atmosphere… (2023). Environmental Chemistry Letters. doi:10.1007/s10311-023-01644-9 CKB 0721
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. Particulate matter (PM₂.₅ and PM₁₀). Coridum Knowledge G-0001, 16 September 2026. https://coridum.com/k/G-0001/