Indoor environment factor · measured in µg/m³ or ppb (1 ppb ≈ 1.25 µg/m³)
Formaldehyde (CH₂O)
Also: HCHO, CH2O, methanal, formaldehyde gas
A colourless gas with a sharp smell, classified as a human carcinogen. Indoors it is released for months to years by pressed-wood furniture, laminate flooring, adhesives, textiles and combustion, making it the most important single volatile organic compound in homes.
Why it matters indoors
Formaldehyde is the simplest aldehyde and one of the most produced chemicals in the world, mostly for resins that glue wood particles into boards. Those resins slowly release formaldehyde back into the air, which is why new furniture, flooring and kitchens raise indoor levels — and why the gas is the reference case for indoor chemical exposure.
Where it comes from indoors
Particleboard, medium-density fibreboard and plywood bonded with urea-formaldehyde resin (furniture, kitchen units, laminate flooring), adhesives, paints and varnishes, permanent-press textiles and carpets, insulation foams, cosmetics and disinfectants, tobacco smoke, gas cooking and candles. It also forms indoors when ozone reacts with terpenes from cleaning products and fragrances.
Health effects
Formaldehyde irritates the eyes, nose and throat at concentrations from around 0.1 mg/m³, and causes burning eyes, coughing and headaches at higher levels. It is classified by the International Agency for Research on Cancer as carcinogenic to humans (Group 1) on the basis of nasopharyngeal cancer and leukaemia in occupationally exposed workers. Associations with childhood asthma and allergic sensitisation have been reported, though the evidence is mixed.
Exposure limits
| Jurisdiction | Value | Averaging time | Source |
|---|---|---|---|
| World Health Organization | 0.1 mg/m³ (100 µg/m³) | 30 minutes | WHO indoor air quality guidelines 2010 |
| European Union (products) | emission limit 0.062 mg/m³ for articles, 0.080 mg/m³ for furniture and wood-based articles, in a test chamber | article emission, from 2026 | Regulation (EU) 2023/1464 |
The EU regulates emissions from products rather than room concentrations. Slovak, UAE and Hong Kong indoor values are being compiled in the indoor air quality limits table.
Converting between the units
Guidelines and instruments report formaldehyde both ways — the WHO guideline in mg/m³, most sensors and much of the North American literature in ppb. At 25 °C and 101.325 kPa one ppb is about 1.23 µg/m³, so the WHO 30-minute guideline of 0.1 mg/m³ is about 81 ppb:
How it is measured
Reference methods pass air through a cartridge that traps formaldehyde for laboratory analysis. Continuous monitoring uses electrochemical sensors selective for formaldehyde; general VOC sensors respond to it but cannot separate it from other compounds, so a dedicated channel is needed to compare against the guideline.
What the studies report
12 of 99 Findings — those with the strongest study design.
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| Atopic dermatitis symptoms | difference 79.2 (19.6–168.4) per 10 % | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0278 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| Atopic dermatitis symptoms | difference 39.9 (14.3–71.2) per 10 % | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0279 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| Atopic dermatitis symptoms | difference 28.0 (6.6–53.7) per 10 % | children aged 6 to 18 years with atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0280 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| Atopic dermatitis symptoms | difference 17.8 (3.9–33.6) per 10 % | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0281 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| Atopic dermatitis symptoms | difference 2.5 per 10 % | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0282 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| — | mean 13.6 | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0283 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| — | mean 18.1 | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0284 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| — | mean 16.5 | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0285 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| — | mean 12.5 | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0286 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| — | mean 10.8 | children with moderate-to-severe atopic dermatitis · home | longitudinal (panel) study of children with moderate-to-severe atopic dermatitis in Seoul: real-time indoor formaldehyde monitoring at home and daily symptom scores (4,789 person-days), generalized linear mixed models adjusted for ambient PM2.5, temperature and relative humidity | F-0287 Harmful Effect of Indoor Formaldehyde on Atopic Dermatitis i… (2021) | machine |
| Birth outcomes | beta -0.056 per 1 z-score | pregnant women and their newborns · home | birth cohort in Western Australia: formaldehyde, nitrogen dioxide and VOCs monitored in the homes of pregnant women at 34 weeks of gestation, associations with birth outcomes adjusted for maternal age, parity, asthma, diabetes, hypertension and season | F-0331 Franklin et al. Maternal Exposure to Indoor Air Pollution and Birth Outcomes (2019) | machine |
| Unvented heaters | difference 9.4 (5.7–13.1) | school children · classroom | double-blind, cluster-randomised crossover trial in Australian school classrooms: low-NOx unflued gas heaters against non-indoor-emitting flued gas heaters, NO2 and formaldehyde measured with passive diffusion badges, children recorded symptoms, medication use and lung function twice daily | F-0690 Respiratory Health Effects of Exposure to Low-NOx Unflued Ga… (2010) | 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
-
Newly installed laminate flooring and wood-based panels may be associated with raised indoor formaldehyde.
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 with a formaldehyde channel use an electrochemical sensor; the general VOC sensor also responds to formaldehyde but cannot distinguish it.
Identifiers
- Molecular formula
- CH₂O
- IUPAC name
- methanal
- CAS Registry Number
- 50-00-0 · PubChem · CTD
- InChIKey
- WSFSSNUMVMOOMR-UHFFFAOYSA-N
- MeSH
- D005557
- SMILES
C=O
Frequently asked questions
What is a safe formaldehyde level indoors?
The WHO guideline is 0.1 mg/m³ (100 µg/m³, about 80 ppb) as a 30-minute average, set to prevent sensory irritation; the WHO considers this also protective against long-term effects including cancer. Many national bodies aim for 30–50 µg/m³ as a long-term target.
How long does formaldehyde off-gas from new furniture?
Emission from urea-formaldehyde resins in particleboard and MDF decays slowly and can continue at measurable levels for years, rising with temperature and humidity. The first weeks after installation are the peak.
Does ventilation help?
Yes, but only while the windows are open — the source keeps emitting. Lasting reduction comes from choosing low-emission (E1 or better, CARB 2) products, sealing exposed board edges, and keeping rooms cool and dry.
Sources
- WHO guidelines for indoor air quality: selected pollutants. World Health Organization Regional Office for Europe, 2010.
- IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100F: Formaldehyde. International Agency for Research on Cancer, 2012.
- Commission Regulation (EU) 2023/1464 amending Annex XVII to REACH as regards formaldehyde and formaldehyde releasers.
- Adsorption of Formaldehyde by Wood Enhances the LowTemperature Formaldehyde Oxidation Performance of Pt/TiO2 (2025). ACS Omega. doi:10.1021/acsomega.5c09800 CKB 1187
- Ham et al. Undeclared Formaldehyde Levels in Patient Consumer Products: Formaldehyde Test Kit Utility (2019). Cutaneous and ocular toxicology. doi:10.1080/15569527.2018.1471485 CKB 0261
- Yang et al. Recent advances in electrochemical sensors for formaldehyde. Molecules (Basel, Switzerland). doi:10.3390/molecules29020327 CKB 0278
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. Formaldehyde (CH₂O). Coridum Knowledge G-0008, 16 September 2026. https://coridum.com/k/G-0008/