Should I get rid of my gas stove?

The measured claim: gas stoves genuinely emit NO2 at levels worth taking seriously in small, unventilated kitchens with children who have asthma — and the fix hierarchy starts far short of replacement. Use the extraction hood every time you cook (vented outdoors if possible), open a window, cook on back burners, and the exposure problem largely resolves; induction is the superior technology on air, safety and performance grounds when replacement time comes anyway. The 12.7% asthma figure that launched the panic is a contested modelling estimate, not a measurement. If your child has asthma and your kitchen is unventilated, act on ventilation this week; nobody needs to ambush a functioning stove for public health reasons.

Do air purifiers actually work?

HEPA filtration works, with the physics beyond dispute and health-endpoint evidence growing: portable HEPA units measurably cut indoor PM2.5, allergens and wildfire smoke, with trials showing benefits for allergy symptoms and some cardiovascular markers, and they earn their place in smoke events, allergy seasons and polluted cities — sized to the room (check clean air delivery rate) and run continuously. What does not work or worse: ozone generators (deliberately emitting a regulated lung irritant — never buy), many ionisers and 'photocatalytic' devices with ozone by-products and weak data, fragrance devices that add VOCs while masking odours, and houseplants, which at realistic densities remove approximately nothing. Ventilation and source control still beat every box you can purchase.

How do I know if radon is a problem in my home?

Only by testing — radon is invisible, odourless, and varies so much building-to-building that regional maps cannot clear an individual house. Testing is cheap and simple: a passive detector placed in the main living area for at least three months (long-term beats short-term; winter concentrations run higher), available from national radon programmes and hardware stores. At or above the WHO reference level of 100 Bq/m³ — national action levels vary to 148-300 — mitigation by sub-slab depressurisation reliably cuts levels dramatically at the cost of a modest home repair. If anyone in the house smokes, the urgency multiplies literally: radon and smoking interact multiplicatively on lung cancer risk.

Is mould in my home dangerous?

For respiratory health, yes in a specific, well-evidenced way: damp and mould consistently associate with asthma development, asthma exacerbation and respiratory infection, particularly in children, and remediation trials show symptom improvement. What the evidence does not support is the expansive 'toxic mould' syndrome attributing systemic multi-organ illness to household mycotoxin exposure — indoor airborne concentrations fall far below toxic thresholds, and 'chronic Lyme'-adjacent mould-illness protocols run ahead of any controlled data. The response is structural, not pharmaceutical: find and fix the moisture source (leaks, condensation, rising damp), remove affected material, ventilate bathrooms and kitchens — and recognise that persistent damp housing is a landlord and housing-standards problem masquerading as a lifestyle one.

What indoor air upgrades give the most health value for money?

In rough order of return: stop indoor smoking and vaping entirely (free, enormous); test for radon and mitigate if high (cheap test, one-off repair); use kitchen and bathroom extraction and fix damp promptly (largely free, high respiratory value); maintain functioning CO and smoke alarms (trivial cost, saves lives outright); upgrade HVAC filters to MERV-13 or run a right-sized HEPA unit where smoke, allergy or pollution justify it; and ventilate deliberately — even scheduled window airing measurably drops CO2 and VOCs. Skip ozone devices, ionisers of unverified pedigree, fragrance systems and plant-based purification. Globally, the same ranking logic puts clean cooking fuel above everything: the greatest indoor-air value for money on Earth is a family's first LPG cylinder.

Did COVID really change indoor air policy?

It changed the framework; implementation is the open question. The pandemic forced formal recognition that respiratory pathogens transmit through shared room air, producing the first ventilation standard explicitly targeting infection risk (ASHRAE 241, 2023), government clean-air-in-buildings programmes, school ventilation funding in several countries and a normalisation of CO2 monitoring as a public-facing ventilation gauge. The unresolved politics: standards are largely voluntary, retrofit money is finite, and energy costs push against outdoor-air volumes — making filtration and heat recovery the realistic path. The historical parallel advocates draw is sanitation: cholera made water infrastructure a public obligation, and the open question is whether shared air eventually acquires the same status.

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Indoor Air Quality

GMJ News knowledge hub · last reviewed August 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

People in high-income settings spend around 90% of their time indoors, and the indoor environment carries both the world’s deadliest confirmed air hazard and some of its most contested new ones. The settled core is enormous: household air pollution from cooking with solid fuels kills roughly 3.2 million people a year, radon is the second leading cause of lung cancer after smoking, second-hand tobacco smoke kills over a million annually, and damp and mould demonstrably worsen asthma. The contested frontier is narrower than headlines suggest — gas stoves genuinely raise indoor nitrogen dioxide and are associated with childhood asthma, but the widely quoted claim that they cause one in eight US childhood asthma cases rests on modelling assumptions that are actively disputed; meanwhile ozone-generating “air purifiers” are marketed as a solution while adding a regulated pollutant to the room (WHO household air pollution fact sheet).

Key messages

SETTLED AND ENORMOUS: household air pollution from solid fuels

The deadliest indoor air problem attracts the least Western attention: roughly 2.1 billion people cook with wood, charcoal, crop waste, dung or coal on open fires and rudimentary stoves, and the resulting household air pollution kills about 3.2 million people a year — pneumonia in children, COPD, ischaemic heart disease, stroke and lung cancer in adults — with women and children bearing the exposure. Clean cooking transition (LPG, electricity, genuinely clean biomass stoves) is among the highest-value interventions in global health, and it dwarfs every contested indoor air question in high-income countries combined.

SETTLED: radon, second-hand smoke, damp and mould

Three further indoor exposures are beyond scientific dispute. Radon — a natural radioactive soil gas accumulating in buildings — is the second cause of lung cancer after smoking and the first among never-smokers, with risk multiplicative in smokers; testing is cheap and mitigation established. Second-hand tobacco smoke kills over a million people yearly and has no safe level — the evidence base behind smoke-free laws, among the most successful health policies ever enacted. And damp and mould consistently associate with asthma development and exacerbation, an exposure concentrated in poor-quality housing and therefore as much a housing-policy issue as a medical one.

GENUINELY CONTESTED: gas stoves — real exposure, disputed magnitude

Gas combustion indoors demonstrably produces nitrogen dioxide at concentrations that can exceed outdoor air standards in unventilated kitchens, and meta-analyses have long associated gas cooking with childhood asthma (a 2013 synthesis estimated over 30% higher odds). The 2022 claim that 12.7% of US childhood asthma is attributable to gas stoves — the number that ignited the political firestorm — applied that older meta-analysis through a population attributable fraction model whose assumptions (causality, transferability, exposure equivalence) are actively disputed, and a large Swedish cohort found no association. The defensible summary: the hazard is real, ventilation is the confirmed remedy, and the headline attributable fraction is a modelling estimate presented with more confidence than it earned.

OPEN AND POST-PANDEMIC: ventilation as infrastructure

COVID-19 converted ventilation from an engineering afterthought into public health policy: recognition of airborne transmission produced the first standards explicitly targeting infection risk (ASHRAE 241 in 2023), national clean-air-in-buildings initiatives and a research agenda on CO2 monitoring as a ventilation proxy. The open questions are economic and normative rather than mechanistic — how much ventilation, at what energy cost, mandated where — because the underlying science (dilution reduces far-field airborne transmission) is established. Indoor air is plausibly the pandemic's most durable public health legacy, and the one least implemented so far.

UNSUPPORTED AND SOMETIMES HARMFUL: the air-cleaning marketplace

The consumer response to indoor air anxiety includes genuinely effective technology and outright harm sold side by side. HEPA filtration demonstrably removes particles and reduces allergen and smoke exposure, with growing trial evidence for health endpoints; ventilation and source control outperform any gadget. Meanwhile ozone-generating 'purifiers' add a regulated lung irritant to the room by design; ionisers and 'plasma' devices can generate ozone and secondary pollutants with thin efficacy data; and houseplants, at any realistic density, do approximately nothing to indoor VOCs — a myth descended from a NASA chamber study misapplied to real rooms. The market rewards the sensation of purification over the removal of pollutants.

THE FRAME: buildings are a health determinant, unequally distributed

People in high-income countries spend about 90% of life indoors, and indoor air integrates every upstream inequity: damp, crowding, gas cooking without ventilation, traffic-adjacent housing, no air conditioning in heatwaves and no filtration in wildfire smoke — which now episodically makes indoor air in affected regions worse than a bad day in any megacity. The gradient runs the same direction globally as locally: the poorest breathe the worst indoor air, from dung smoke in rural kitchens to mould in social housing. Treating indoor air as infrastructure — building codes, housing standards, school ventilation — rather than as consumer self-protection is where the evidence points and the disparities close.

Key statistics

3.2 million

deaths per year from household air pollution, overwhelmingly from cooking with solid fuels

WHO

2.1 billion

people still relying on polluting fuels and technologies for cooking

WHO/IEA

radon’s rank among causes of lung cancer — first among never-smokers; 3-14% of lung cancers by country

WHO

1.2 million+

annual deaths attributed to second-hand smoke exposure — no safe level exists

WHO

12.7%

the contested modelled share of US childhood asthma attributed to gas stoves — an estimate, not a measurement

Gruenwald et al. 2022

~90%

share of time spent indoors in high-income countries — the case for treating buildings as a health determinant

Exposure science

Indoor air — where the disagreement actually lies

Source: Bars show strength of supporting evidence. High values indicate well-supported propositions; low values indicate claims tested and not supported.

Glossary of key terms

Household air pollution and the energy ladder
Global healthThe 'energy ladder' runs from dung and crop residues through wood and charcoal to kerosene, LPG, biogas and electricity, with indoor emissions falling by orders of magnitude on the climb. Burning solid fuel indoors produces PM2.5 at concentrations that can exceed WHO guideline values a hundred-fold, and the exposure is structured by gender and age — women cooking and infants carried beside the fire. WHO defines clean cooking by emission performance rather than fuel identity, and the disappointing trial history of 'improved' biomass cookstoves (real emission cuts, largely unrealised health gains in trials such as HAPIN) has shifted the field toward genuinely clean fuels — making clean cooking access, tracked under SDG 7, the pragmatic frontline of indoor air.

Radon: testing and mitigation
Environmental healthRadon is a decay product of uranium in soil and rock — an odourless radioactive gas that seeps through foundations and concentrates indoors, with enormous variation between neighbouring buildings. Its alpha-emitting progeny lodge in airway epithelium; pooled European case-control studies established lung cancer risk rising about 16% per 100 Bq/m³ long-term exposure with no evident threshold, and the smoker-radon combination is multiplicative. WHO recommends a 100 Bq/m³ reference level. The public health frustration is that everything works and little happens: testing costs little, sub-slab depressurisation reliably cuts concentrations, yet testing rates stay low even in mapped high-radon zones — a pure implementation failure.

Nitrogen dioxide and the gas stove evidence
EvidenceGas flames fix atmospheric nitrogen into NO2, an airway irritant with established respiratory effects from outdoor pollution science, and kitchen measurements confirm unvented gas cooking can push indoor NO2 past one-hour outdoor standards. The association with childhood asthma appeared in meta-analysis a decade before the controversy — the 2013 synthesis reporting roughly 32% higher odds — but individual studies conflict (a large Swedish cohort found no association), exposure varies enormously with ventilation and stove use, and causality versus correlated housing factors remains arguable. The 12.7% attributable fraction that dominated headlines multiplied the older meta-analytic odds ratio through gas-stove prevalence — methodologically standard, assumption-laden, and defensible only with the uncertainty attached, which the ensuing culture war removed in both directions.

Volatile organic compounds and formaldehyde
Exposure scienceIndoor VOC concentrations typically run several-fold above outdoor levels, emitted by building materials, furnishings, paints, adhesives, cleaning products and fragrances — with formaldehyde (a Group 1 carcinogen at occupational exposures, released by composite wood products) the best characterised. Established effects at typical home concentrations are mainly irritant and inconsistently linked to asthma; the honest position is that chronic low-level mixture effects are under-studied rather than exonerated. Practical control is source-side and cheap: low-emission certified materials, airing new furnishings, moderate use of fragranced products, ventilation during and after painting — a hierarchy in which buying a VOC-sensing gadget ranks last.

Ventilation metrics: ACH, CO2 and ASHRAE 241
EngineeringVentilation is measured in air changes per hour (ACH) or litres per second per person; occupant-generated CO2 serves as a convenient proxy for how much exhaled air accumulates — outdoors ~420 ppm, well-ventilated rooms under ~800, stuffy classrooms often far beyond. COVID-19 produced the first standard written for infection risk: ASHRAE 241 (2023) defines equivalent clean airflow targets per occupant for infection-risk-management mode, combinable from outdoor air, filtration (MERV-13 and above) and validated air cleaning including far-UVC. The unresolved tension is energy: every litre of conditioned outdoor air costs carbon, which is why heat-recovery ventilation and filtration-heavy strategies dominate serious retrofit designs.

Wildfire smoke and the indoor refuge problem
Climate/HealthClimate-driven wildfire seasons have created a recurring inversion: regions with historically clean air experiencing weeks when outdoor PM2.5 exceeds hazardous thresholds and the official advice is 'stay indoors' — which only helps if indoors is actually cleaner. Leaky buildings without filtration converge toward outdoor concentrations within hours; homes with recirculating HVAC on MERV-13 filters or portable HEPA units maintain PM2.5 at small fractions of outdoor levels, and the do-it-yourself box-fan filter (Corsi-Rosenthal) performs respectably in published tests for tens of dollars. Smoke readiness — filtration capacity, sealed rooms, N95s for unavoidable outdoor time — is becoming a standard preparedness domain alongside heat, and access to it tracks income precisely.