Indoor environment factor · measured in ppm or mg/m³ (1 ppm ≈ 1.15 mg/m³)
Carbon monoxide (CO)
Also: CO
A colourless, odourless, toxic gas produced by incomplete combustion — distinct from carbon dioxide. It binds to haemoglobin far more strongly than oxygen does, starving tissues of oxygen at concentrations that cannot be seen, smelled or felt until symptoms appear.
Why it matters indoors
Carbon monoxide forms whenever a fuel burns without enough oxygen to complete the reaction. It is the most common cause of fatal poisoning in homes in Europe, precisely because it gives no sensory warning: the gas is invisible, has no smell and the early symptoms resemble ordinary illness.
Where it comes from indoors
Faulty or poorly vented gas boilers and water heaters, blocked chimneys, gas cooking without extraction, solid-fuel stoves and fireplaces, portable heaters burning gas or paraffin, charcoal barbecues used indoors, and vehicle exhaust from attached garages. Tobacco smoke adds a small, continuous contribution.
Health effects
Carbon monoxide binds to haemoglobin about 240 times more strongly than oxygen, forming carboxyhaemoglobin and reducing the blood’s capacity to carry oxygen. Low chronic exposure causes headaches, fatigue and impaired concentration and worsens cardiovascular disease; unborn children and people with heart disease are most vulnerable. High exposure leads to loss of consciousness and death within minutes to hours.
Exposure limits
| Jurisdiction | Value | Averaging time | Source |
|---|---|---|---|
| World Health Organization | 100 mg/m³ (≈ 87 ppm) | 15 minutes | WHO indoor air quality guidelines 2010 |
| World Health Organization | 35 mg/m³ (≈ 30 ppm) | 1 hour | WHO indoor air quality guidelines 2010 |
| World Health Organization | 10 mg/m³ (≈ 9 ppm) | 8 hours | WHO indoor air quality guidelines 2010 |
| World Health Organization | 7 mg/m³ (≈ 6 ppm) | 24 hours | WHO indoor air quality guidelines 2010 |
| World Health Organization (ambient) | 4 mg/m³ | 24 hours | WHO AQG 2021 |
Slovak, UAE and Hong Kong values are being compiled in the indoor air quality limits table.
How it is measured
Electrochemical cells generate a current proportional to the carbon monoxide concentration; they are selective, sensitive to below 1 ppm, and last several years. Every monitor that includes a carbon monoxide channel should be treated as a safety device with an audible or push alarm, not just a logger.
What the studies report
12 of 259 Findings — those with the strongest study design.
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| — | other 0.47 | — · personal exposure of the cook | systematic review and pooled analysis of paired PM2.5 and carbon-monoxide measurements from studies in households where biomass was the dominant fuel: regression of ln(PM2.5) on ln(CO) for personal exposure and for cooking-area measurements, with covariates and a random intercept for each study | F-0980 Carter Assessing Exposure to Household Air Pollution: A Systematic … (2017) | machine |
| — | other 0.46 | — · kitchen | systematic review and pooled analysis of paired PM2.5 and carbon-monoxide measurements from studies in households where biomass was the dominant fuel: regression of ln(PM2.5) on ln(CO) for personal exposure and for cooking-area measurements, with covariates and a random intercept for each study | F-0981 Carter Assessing Exposure to Household Air Pollution: A Systematic … (2017) | machine |
| Biomass fuel | mean 18.82 | — · home | review of studies of indoor air pollution in Ethiopian households with calculated mean concentrations across the included studies: particulate matter, nitrogen dioxide, total volatile organic compounds, polycyclic aromatic hydrocarbons and carbon monoxide, by geography, stove type and household activity | F-1003 Asefa Human exposure to indoor air pollution in Ethiopian househol… (2022) | machine |
| Clean fuels | median 0.52 | — · personal exposure of pregnant women | multi-country randomised controlled trial in pregnant women (HAPIN): households were assigned a liquefied petroleum gas stove and fuel, an improved biomass stove, or usual cooking, with personal carbon monoxide and fine particulate matter measured after the intervention | F-1777 A cluster randomised trial of cookstove interventions to imp… (2021) | machine |
| Improved cookstoves | median 0.74 | — · personal exposure of pregnant women | multi-country randomised controlled trial in pregnant women (HAPIN): households were assigned a liquefied petroleum gas stove and fuel, an improved biomass stove, or usual cooking, with personal carbon monoxide and fine particulate matter measured after the intervention | F-1778 A cluster randomised trial of cookstove interventions to imp… (2021) | machine |
| Cookstoves | mean 19 | primary cooks · personal exposure of the primary cook in the household | quasi-experimental evaluation of two improved cookstove programmes in Lusaka, Zambia: 24-hour personal exposure to carbon monoxide (747 measurements) and PM2.5 (90) of primary cooks at baseline in the cool season of 2019 and at endline in the warm season, with difference-in-differences and generalised least squares models of log-transformed exposure against stove group, season, neighbourhood, cooking location, ventilation, stove-influenced hours and expenditure | F-0711 Impacts of Improved Cookstove Interventions on Personal Expo… (2025) | machine |
| Charcoal | mean 18 | primary cooks · personal exposure of the primary cook in the household | quasi-experimental evaluation of two improved cookstove programmes in Lusaka, Zambia: 24-hour personal exposure to carbon monoxide (747 measurements) and PM2.5 (90) of primary cooks at baseline in the cool season of 2019 and at endline in the warm season, with difference-in-differences and generalised least squares models of log-transformed exposure against stove group, season, neighbourhood, cooking location, ventilation, stove-influenced hours and expenditure | F-0712 Impacts of Improved Cookstove Interventions on Personal Expo… (2025) | machine |
| Charcoal | mean 14 | primary cooks · personal exposure of the primary cook in the household | quasi-experimental evaluation of two improved cookstove programmes in Lusaka, Zambia: 24-hour personal exposure to carbon monoxide (747 measurements) and PM2.5 (90) of primary cooks at baseline in the cool season of 2019 and at endline in the warm season, with difference-in-differences and generalised least squares models of log-transformed exposure against stove group, season, neighbourhood, cooking location, ventilation, stove-influenced hours and expenditure | F-0713 Impacts of Improved Cookstove Interventions on Personal Expo… (2025) | machine |
| Charcoal | mean 14 | primary cooks · personal exposure of the primary cook in the household | quasi-experimental evaluation of two improved cookstove programmes in Lusaka, Zambia: 24-hour personal exposure to carbon monoxide (747 measurements) and PM2.5 (90) of primary cooks at baseline in the cool season of 2019 and at endline in the warm season, with difference-in-differences and generalised least squares models of log-transformed exposure against stove group, season, neighbourhood, cooking location, ventilation, stove-influenced hours and expenditure | F-0714 Impacts of Improved Cookstove Interventions on Personal Expo… (2025) | machine |
| Charcoal | mean 9 | primary cooks · personal exposure of the primary cook in the household | quasi-experimental evaluation of two improved cookstove programmes in Lusaka, Zambia: 24-hour personal exposure to carbon monoxide (747 measurements) and PM2.5 (90) of primary cooks at baseline in the cool season of 2019 and at endline in the warm season, with difference-in-differences and generalised least squares models of log-transformed exposure against stove group, season, neighbourhood, cooking location, ventilation, stove-influenced hours and expenditure | F-0715 Impacts of Improved Cookstove Interventions on Personal Expo… (2025) | machine |
| — | difference 78 | primary cooks · personal exposure of the primary cook in the household | quasi-experimental evaluation of two improved cookstove programmes in Lusaka, Zambia: 24-hour personal exposure to carbon monoxide (747 measurements) and PM2.5 (90) of primary cooks at baseline in the cool season of 2019 and at endline in the warm season, with difference-in-differences and generalised least squares models of log-transformed exposure against stove group, season, neighbourhood, cooking location, ventilation, stove-influenced hours and expenditure | F-0716 Impacts of Improved Cookstove Interventions on Personal Expo… (2025) | machine |
| — | difference 44 | primary cooks · personal exposure of the primary cook in the household | quasi-experimental evaluation of two improved cookstove programmes in Lusaka, Zambia: 24-hour personal exposure to carbon monoxide (747 measurements) and PM2.5 (90) of primary cooks at baseline in the cool season of 2019 and at endline in the warm season, with difference-in-differences and generalised least squares models of log-transformed exposure against stove group, season, neighbourhood, cooking location, ventilation, stove-influenced hours and expenditure | F-0717 Impacts of Improved Cookstove Interventions on Personal Expo… (2025) | 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 Coridum measures it: Coridum devices use an electrochemical cell specific to carbon monoxide; alarm thresholds follow WHO short-term limits and trigger immediate notifications.
Identifiers
- Molecular formula
- CO
- IUPAC name
- carbon monoxide
- CAS Registry Number
- 630-08-0 · PubChem · CTD
- InChIKey
- UGFAIRIUMAVXCW-UHFFFAOYSA-N
- MeSH
- D002248
- SMILES
[C-]#[O+]
Frequently asked questions
What are the first symptoms of carbon monoxide poisoning?
Headache, dizziness, nausea, weakness and confusion — easily mistaken for flu or food poisoning. The tell-tale signs are symptoms that improve when you leave the building and affect several people in the same room, including pets.
Which appliances cause carbon monoxide indoors?
Any fuel-burning appliance that is faulty, poorly maintained or badly vented: gas boilers and water heaters, gas hobs and ovens, wood and coal stoves, fireplaces, portable gas or paraffin heaters, and engines running in attached garages.
Does a CO₂ sensor detect carbon monoxide?
No. They are different gases requiring different sensors. A room can have normal CO₂ and lethal carbon monoxide at the same time.
Sources
- WHO guidelines for indoor air quality: selected pollutants. World Health Organization Regional Office for Europe, 2010.
- WHO global air quality guidelines. World Health Organization, 2021.
- Salthammer Carbon monoxide as an indicator of indoor air quality (2024). doi:10.1039/d4ea00006d CKB 0961
- Investigation of indoor air quality inside houses from UAE (2020). Air, Soil and Water Research. doi:10.1177/1178622120928912 CKB 0038
- Carbon monoxide formation from total volatile organic compounds from the use of household spray products (2023). Journal of Air Pollution and Health. doi:10.18502/japh.v8i3.13790 CKB 0209
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. Carbon monoxide (CO). Coridum Knowledge G-0004, 16 September 2026. https://coridum.com/k/G-0004/