At a glance
| Chemical family | A radioactive noble gas from the natural decay of uranium in soil and rock; filed under building & environmental sources |
| CAS number | 14859-67-7 (radon-222) |
| Classification | IARC / WHO Group 1 — carcinogenic to humans (lung cancer). Second leading cause of lung cancer overall; first among never-smokers |
| Where you encounter it | Indoor air, drawn up from the ground through foundation cracks and gaps; concentrates in basements and lower-level rooms |
| Sleep micro-environment relevance | Accumulates in the lowest occupied levels — frequently bedrooms — where you breathe it for roughly a third of every day |
| Activated carbon capture | Not the lever for a home — the documented fix is sub-slab depressurization (radon mitigation); testing comes first |
What it is
Radon-222 is a radioactive gas, the decay product of uranium that occurs naturally throughout the earth's crust. Because it is a noble gas it is chemically inert — it does not react, bind or smell — but it is radioactive, and as it and its short-lived "decay products" break down they emit alpha particles that can damage the DNA of the cells lining the lung. Regulatory — US EPA, Health Risk of Radon It is everywhere at low levels outdoors, where it disperses; the hazard is entirely about what happens when it collects inside a building.
That makes radon unlike anything else in this Atlas. It is not manufactured, not added to a product, not a residue. It is the ground's own contribution to the air indoors — and it accounts for about half of the average person's exposure to natural ionizing radiation. Regulatory — US EPA / WHO International Radon Project
How it relates to the bedroom
Why it concentrates where you sleep
Radon enters a home from below. Soil gas carrying radon is drawn through cracks in the slab, gaps around pipes, sump openings and unsealed foundations by the slight suction a heated building exerts on the ground beneath it. Because it comes from underneath, it concentrates in the lowest occupied levels — basements and ground-floor rooms, which in a great many homes are bedrooms. Inferred — radon's soil-gas entry route concentrates it in lower levels; bedrooms are commonly among them And the bedroom is where a chronic inhalation exposure does its quiet work: you breathe one room's air, undisturbed, for roughly a third of your life. A modest concentration met for eight hours every night is exactly the exposure pattern radon risk is built on.
A serious, well-measured risk
The evidence here is unusually strong, because radon has been studied for decades — first in underground miners, then directly in homes. Two landmark pooled analyses settled the residential question. The European collaboration, combining 13 studies and over 7,000 lung-cancer cases, found that risk rose by about 16% for every 100 Bq/m³ of usual home radon, along a straight line with no safe threshold — the effect held even below 200 Bq/m³. Peer-reviewed — Darby et al. 2004 The North American pooling of seven studies reached the same conclusion and matched the predictions extrapolated from the miner data, supporting estimates that radon drives 10–15% of lung-cancer deaths. Peer-reviewed — Krewski et al. 2006 Regulators put the toll at roughly 21,000 US lung-cancer deaths a year, making radon the second leading cause after smoking and the leading cause among non-smokers. Regulatory — US EPA, Health Risk of Radon (BEIR VI)
The smoking multiplier
One fact reframes the whole risk: radon and tobacco smoke act together, and the combination is far worse than either alone. The proportional increase in risk per unit of radon is similar for smokers and non-smokers, but smokers start from a vastly higher baseline — so their absolute radon-related risk is on the order of 25 times that of lifelong non-smokers. Peer-reviewed — Darby et al. 2004 In EPA's framing, at the 4 pCi/L action level about 62 of 1,000 lifelong smokers would be expected to die of lung cancer versus about 7 of 1,000 who never smoked. Regulatory — US EPA, Health Risk of Radon For a smoker, reducing radon and quitting tobacco attack the same danger from two sides.
What the research says
- Group 1 carcinogen; #2 cause of lung cancer. ~21,000 US deaths a year; first cause among never-smokers. Regulatory — US EPA (BEIR VI)
- Risk rises with home level, no threshold. +16% per 100 Bq/m³; significant even at low concentrations. Peer-reviewed — Darby et al. 2004
- Confirmed across continents. North American pooling matches European and miner data. Peer-reviewed — Krewski et al. 2006
- Smoking multiplies it. Smokers' absolute radon risk ~25× that of non-smokers. Peer-reviewed — Darby et al. 2004
What helps reduce it
Test first — it is cheap and definitive. A short-term kit or a digital monitor reveals your level; you cannot know it any other way. The EPA recommends acting at 4 pCi/L (150 Bq/m³) and considering action between 2 and 4. Regulatory — US EPA, Health Risk of Radon
Mitigate if it is high. Sub-slab depressurization — a fan and vent pipe that intercepts soil gas before it enters — reliably lowers indoor radon, the same engineered approach used for solvent vapor intrusion. Inferred — radon mitigation is the established sub-slab method
If you smoke, quit. It removes the multiplier that makes radon most lethal — the single biggest lever a radon-exposed smoker has. Peer-reviewed — Darby et al. 2004
What does NOT help
- A "cleaner" mattress or bedding. Radon is a soil gas; nothing about the bed affects it. Inferred
- Ordinary air purifiers as a fix. Filtration does not address a continuously replenished soil-gas source; mitigation at the foundation does. Inferred
Open research questions
- How much of the measured residential-radon risk at low levels reflects radon itself versus co-varying indoor particulate pollution. Speculation
- Whether bedroom-specific (versus whole-home) radon measurement better predicts individual risk given sleep-time exposure. Speculation
Citations
- US EPA, Health Risk of Radon (incorporating BEIR VI, National Academy of Sciences 1999; EPA 402-R-03-003). Radon the #1 cause of lung cancer in non-smokers and #2 overall; ~21,000 US deaths/year (~2,900 never-smokers); action level 4 pCi/L; smoking synergy. US EPA Regulatory
- Darby S, et al. (2004). Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. BMJ. +16% lung-cancer risk per 100 Bq/m³ usual radon; linear, no threshold; smokers' absolute risk ~25× non-smokers. Via Consensus. Reference record Peer-reviewed
- Krewski D, et al. (2006). A combined analysis of North American case-control studies of residential radon and lung cancer. J. Toxicol. Environ. Health A. Pooled 7 studies (4,081 cases); risk rises with radon; consistent with miner extrapolation; supports 10–15% of lung-cancer deaths. Via Consensus. Reference record Peer-reviewed
Frequently asked questions
What is radon and where does it come from?
Radon-222 is a radioactive gas produced by the natural decay of uranium in soil and rock. It is colorless, odorless and tasteless, so you cannot sense it. It seeps out of the ground everywhere, but outdoors it disperses harmlessly; the problem is that it can collect indoors, drawn up through a building's foundation, where it builds to concentrations far above the outdoor background.
Why is the bedroom relevant?
Radon enters from below and accumulates in the lowest occupied levels of a home — basements and ground-floor rooms, which often include bedrooms. Since you spend roughly a third of your life asleep, breathing the air of one room for hours every night, the bedroom is exactly where a chronic inhalation exposure like radon matters most. It is the ground's contribution to the air you sleep in.
How serious is the risk?
Serious, and well established. Radon is the second leading cause of lung cancer overall and the leading cause among people who have never smoked, responsible for an estimated 21,000 lung-cancer deaths a year in the United States. Large pooled studies in Europe and North America show lung-cancer risk rising steadily with home radon levels, with no clear safe threshold. The risk is dramatically higher for smokers, because radon and tobacco smoke act together.
What should I do about it?
This is the encouraging part: radon is both easy to measure and fixable. Inexpensive test kits or digital monitors tell you your level; the EPA recommends acting at 4 pCi/L (150 Bq/m3) and considering it between 2 and 4. If your level is high, a radon mitigation system — typically sub-slab depressurization, a fan and vent pipe that draws soil gas away before it enters — reliably brings it down. If you smoke, quitting removes the multiplier that makes radon most dangerous.
Related compounds
Embr is a sleep environment company researching and addressing the chemistry of the bedroom. Research and product development in progress.
Last reviewed 2026-06-27. If you find a factual error, contact us.