Indoor Air in French Homes: What the 2025 OQEI Report Reveals
The Essential
France's second National Housing Campaign (CNL2), published by the OQEI in June 2025, measured over 170 pollutants in 571 representative households. Nearly all targeted substances were found in more than half of homes surveyed. 70% of homes exceed the 10 µg/m³ target for fine particles PM2.5 set by France's High Council for Public Health (HCSP) for 2025. Indoor air quality has improved since the first campaign (2003-2005), but levels of several pollutants remain a concern - particularly in older and poorly ventilated housing. These findings are relevant to anyone spending most of their time indoors in France.
We tend to think of air pollution as an outdoor problem - city traffic, industrial emissions, wildfire smoke. The data tells a different story.
In June 2025, France's Observatory for the Quality of Indoor Environments (OQEI, formerly OQAI) published the results of its second National Housing Campaign (CNL2), covering 571 homes across 84 of France's 96 departments. With over 170 pollutants analyzed, it is the most comprehensive study ever conducted on indoor air quality in French residential buildings.
The headline finding is clear: indoor air pollution is widespread, not exceptional. But the picture is nuanced - a genuine improvement since the 2003-2005 baseline, alongside persistent gaps that the science community and policymakers cannot yet claim to have closed. For a full overview: indoor air quality: breathe cleaner at home.
What the OQEI Measured - and How
The OQEI (previously OQAI) was created in 2001 to provide an independent scientific foundation for indoor air quality policy in France. In January 2024, it broadened its scope to include noise, light, and thermal comfort, becoming the Observatory for the Quality of Indoor Environments.
The CNL2 methodology is what gives it statistical credibility: 571 households selected by random sampling, weighted to represent France's 29.7 million primary residences. Sensors were installed for one week in the living room and main bedroom of each home, capturing real-world concentrations rather than lab estimates. Occupant questionnaires on habits, equipment, and health perceptions completed the picture.
Pollutant by Pollutant: The Key Findings
Fine Particles PM2.5: The Headline Number
PM2.5 - airborne particles smaller than 2.5 micrometers in diameter - can penetrate deep into lung tissue and enter the bloodstream. Indoor sources include cooking, candles and incense, wood burning stoves, and infiltration from outdoor air.
The CNL2 finding: 70% of French homes exceed the 10 µg/m³ target set by the HCSP for 2025. 11% exceed the 50 µg/m³ rapid action threshold, the level at which corrective measures are formally recommended.
70 %
of French homes exceed the 2025 PM2.5 target of 10 µg/m³ set by France's High Council for Public Health (HCSP).
Source: OQEI - National Housing Campaign 2, June 2025.
Formaldehyde: A Confirmed Carcinogen in Most Homes
The median formaldehyde concentration across surveyed homes was 14 µg/m³ - below the HCSP's provisional management threshold of 30 µg/m³, but 6% of homes exceeded that level. Classified as a confirmed human carcinogen by the International Agency for Research on Cancer (IARC, Group 1), formaldehyde off-gasses primarily from composite wood panels (MDF, chipboard), furniture adhesives, and paints and varnishes.
Radon: A Geological Risk Underestimated
Radon is a naturally occurring radioactive gas produced by the decay of uranium in certain rock formations - granite, schist. It seeps into homes through foundations and cracks. After tobacco, it is the second leading cause of lung cancer in France (IRSN, 2023 data). The CNL2 found that 8% of surveyed homes exceed the regulatory threshold of 300 Bq/m³. The highest-risk zones correspond to France's granite regions: Massif Central, Brittany, Vosges, Alps.
Benzene, NO₂ and CO₂: Signals Worth Monitoring
Benzene, a confirmed carcinogen, had a median concentration of 1.2 µg/m³ in surveyed homes. The HCSP management reference value of 6 µg/m³ was exceeded in 1.4% of homes. Nitrogen dioxide (NO₂), produced by gas stoves and combustion heating systems, exceeded the WHO daily guideline of 25 µg/m³ in 3% of homes. The median CO₂ level in bedrooms was 783 ppm - a signal of insufficient air renewal. Night-time peaks frequently exceeded 1,000 ppm, the threshold above which sleep quality and cognitive performance begin to decline (Satish et al., Environmental Health Perspectives, 2012).
Pesticides: An Unexpected Finding (PestiLoge Study)
A companion study funded by France's ANSES and published in November 2025 detected pesticide residues in the air and dust of French homes - including households where occupants reported no domestic pesticide use. Transfer from nearby green spaces and multi-year persistence in household dust are suspected mechanisms.
Twenty Years of Progress - Still Not Enough
Comparison with the CNL1 (2003-2005) is the report's main good news: concentrations have fallen across most pollutant categories. The largest decreases involve chlorinated volatile organic compounds (trichloroethylene, tetrachloroethylene, 1,4-dichlorobenzene), as well as benzene, PM2.5, and formaldehyde.
The OQEI attributes this progress to three concurrent drivers: regulation (bans on specific substances; mandatory VOC labeling on construction materials, introduced in France in 2012), falling rates of indoor smoking, and growing public awareness of indoor air quality issues.
Progress is real. But it is incomplete. The 2025 PM2.5 target is missed in seven out of ten homes. And the current drive to improve building energy efficiency - through tighter insulation - risks partly reversing these gains if it is not systematically paired with adequate mechanical ventilation.
Where France Stands in Europe
France is not an outlier. Across Europe, available studies on residential indoor air quality converge on the same priority pollutants: formaldehyde (building materials), PM2.5 (cooking, heating, outdoor infiltration), radon (local geology), NO₂ (combustion appliances).
In the United Kingdom, the UK Health Security Agency (UKHSA) and DEFRA document identical concerns: formaldehyde from furniture, NO₂ from gas cookers, radon concentrated in southwest England and Wales. Post-Brexit, the UK has maintained alignment with WHO recommendations while developing its own guidance framework. Measurement campaigns in older housing stock (Victorian-era homes) reveal pollution levels sometimes higher than the French average.
In Germany, the Umweltbundesamt (UBA) has issued health-based indoor air guidance values with strengthened mandatory labeling requirements on construction products. The result: generally lower VOC levels than France, but a comparable radon risk in granite regions.
A shared European paradox deserves attention: the countries with the best energy performance in buildings (Nordic countries, Germany) are precisely those facing the highest risk of degraded indoor air quality, when mechanical ventilation systems are not properly maintained or replaced. Insulation without ventilation concentrates pollutants. This applies to France as current renovation efforts accelerate.
At the regulatory level, the European Commission has launched work to incorporate indoor air quality requirements into building regulations, as part of its Zero Pollution Action Plan. The CNL2's methodology has been cited as a model for this European-level standardization effort.
What You Can Do
Three practical levers are within reach of any household.
- Control the sources: prioritize low-emission materials and furniture (EU A+ label or equivalent), reduce use of scented candles and incense, avoid wood burning in poorly ventilated rooms, test your home for radon if you live in a high-risk geological zone.
- Ventilate consistently: open windows for at least 10 to 15 minutes daily even in winter, use the range hood when cooking, maintain your mechanical ventilation system (if fitted) and replace filters regularly.
- Purify the air: a well-designed air purifier can significantly reduce concentrations of the key pollutants identified in the CNL2 - PM2.5, bacteria, and allergens. Consult our complete guide to choosing an air purifier.
Concerned about the air quality in your home?
TEQOYA air purifiers are designed and assembled in France, require no disposable filters, and have been independently tested on the pollutants identified in the CNL2: PM2.5, bacteria, allergens, and fine particles. They use ozone-free air ionization technology: they produce negative ions that charge pollutant particles and eliminate them from the air by electrostatic precipitation.
Easy to maintain, energy-efficient, with no disposable filters, the TEQOYA T200 (for small rooms) and TEQOYA T450 (for larger rooms) operate in complete silence.
Unlike HEPA filters that must be replaced regularly, a simple wipe-down is all it takes to maintain the full efficiency of a TEQOYA air purifier throughout its lifetime.
Conclusion
The 2025 OQEI report provides an evidence-based picture of indoor air quality in French homes: better than twenty years ago, but still falling short of health targets for fine particles and several other substances. The progress made since 2003 demonstrates that regulation and public education work. What remains to be done makes clear that indoor air quality does not improve on its own - and that newer, more airtight homes are not automatically healthier ones.
Across Europe, the next frontier is ventilation: ensuring adequate air renewal where insulation has reduced natural exchange. This is not a technically unsolvable problem. It is a question of prioritization.
Frequently Asked Questions
What is the OQEI?
The OQEI (Observatoire de la Qualité des Environnements Intérieurs - Indoor Environment Quality Observatory) is an independent French scientific body created in 2001, affiliated with the Scientific and Technical Centre for Building (CSTB). It monitors indoor air quality in French homes, schools, and offices. Known as OQAI until January 2024, it expanded its scope to include noise, light, and thermal comfort when it adopted its current name.
Is indoor air quality really worse than outdoor air quality?
In most cases, yes - particularly in urban environments. Indoor spaces can contain higher concentrations of certain pollutants (formaldehyde, particulate matter from cooking, radon, biological particles) than the outdoor air, because there is less natural dilution. The OQEI CNL2 data confirms this: virtually all targeted substances were detected in more than half of French homes, often at levels that exceed health-based reference values.
How do I reduce PM2.5 levels in my home?
PM2.5 in homes comes from both indoor sources and outdoor infiltration. To reduce indoor generation: avoid wood burning in enclosed spaces, limit use of candles and incense, use a range hood when cooking. To limit outdoor infiltration: keep windows closed during outdoor pollution episodes. To actively reduce concentration: a certified air purifier reduces airborne fine particles in real-time. Regular ventilation (10-15 minutes daily) remains essential to dilute all indoor pollutants.
What is radon and how do I know if my home is at risk?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in certain geological formations - granite, schist. It seeps into buildings through foundations, floors, and cracks. In France, the highest-risk zones are Brittany, the Massif Central, the Vosges, and the Alpine foothills. A passive radon dosimeter (available from pharmacies or local authorities) can measure concentration over several weeks. If the result exceeds 300 Bq/m³ (France's regulatory threshold), remediation - typically improved sub-slab ventilation - is recommended.
Which air purifier actually removes formaldehyde from home air?
Formaldehyde is one of the most difficult indoor air pollutants to capture because it is highly volatile and present at low concentrations. Activated carbon can adsorb formaldehyde in theory, but at the concentrations found in homes it offers limited capture efficiency and carries a risk of desorption when conditions change. The most effective and evidence-based approach remains source reduction - choosing low-emission furniture and materials (A+ label or equivalent), ventilating consistently, and allowing new furniture to off-gas in a ventilated space before installation in a living room.
Sources
- OQEI (Observatoire de la Qualité des Environnements Intérieurs), "Campagne Nationale Logements 2 (CNL2) - Campaign Report," June 2025. oqei.fr
- OQEI, "PestiLoge Study: Presence of Pesticides in the Air and Dust of French Homes," November 2025. oqei.fr
- International Agency for Research on Cancer (IARC), "Formaldehyde - Monographs Volume 88," World Health Organization, 2004.
- World Health Organization, "WHO Global Air Quality Guidelines," 2021. who.int
- Institut de Radioprotection et de Sûreté Nucléaire (IRSN), "Radon in French homes: levels and determinants." irsn.fr
- Satish U. et al., "Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance," Environmental Health Perspectives, vol. 120, no. 12, 2012.
- UK Health Security Agency (UKHSA) / DEFRA, "Indoor air quality: evidence review for guidance."
- Umweltbundesamt (UBA, Germany), "Indoor air - health-based guidance values."
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