Short answer
Radon breaks down into radioactive particles that lodge in the airways and release alpha radiation, which can damage the DNA of lung cells. Cells repair most of it, but some mistakes are copied as cells divide, and nothing reverses them afterwards. You feel nothing, and cancer can show up many years later. Fixing radon stops new damage and lowers future risk, but it can’t repair what’s already happened.
Key facts
- The harm comes from radon’s decay products, which release alpha radiation inside the airways.
- Damaged DNA that is copied wrongly stays in that cell line. There is no treatment that reverses it.
- There are no symptoms while it happens. Effects typically appear years to decades later.
- Lowering radon stops new damage. Risk from older exposure fades slowly with time, but doesn’t disappear.
What happens when you breathe it in
Radon gas is mostly breathed back out. The trouble starts with what it becomes. Radon has a half-life of 3.8 days, and in the air of a room it keeps breaking down into decay products, mainly isotopes of polonium. These are solid particles. They cling to dust and droplets in the air, and when you inhale, they stick to the lining of your airways.
There they keep decaying, and each decay releases alpha radiation. An alpha particle doesn’t travel far, but the cells it passes through are the ones right next to it: the lining of your bronchial tubes. At that range it is a strong source of DNA damage. Canada’s radon guidance and the World Health Organization both describe lung cancer as the health effect that follows.
Why the damage can’t be undone
Cells are good at repairing broken DNA. Most breaks are fixed correctly. Some are not: a repair can leave a small change in the genetic code. When that cell divides, the change is copied into every cell that comes from it. A single change doesn’t make a cancer. Cancer develops when changes accumulate in the same line of cells, which is why more years of exposure mean more chances for it to happen.
Two things follow from that, and they’re the reason radon is taken seriously:
- Nothing reverses a mutation that has already been copied. There is no treatment, supplement or air purifier that goes back into the lung and corrects it. And there is no medical test for how much radon you’ve breathed in.
- Each year adds to the total. The risk comes from the whole history of exposure, not from the latest reading, which is why Health Canada’s guideline is built on a yearly average and long-term tests.
Why you won’t feel it
Radon doesn’t cause coughing, headaches or any other short-term symptom. The cell-level damage is silent, and cancer, if it comes, usually takes years to decades to appear. The U.S. agency ATSDR notes that radon exposure in childhood may not show up as a health effect until adulthood. That delay is why people assume a home is fine because nobody has been sick, and why a test is the only way to know.
What lowering radon changes, and what it doesn’t
| Does mitigation change it? | |
|---|---|
| Cell damage that has already happened | No. It can’t be repaired or removed by lowering radon afterwards. |
| New damage from this point on | Yes. A properly installed system typically cuts radon by 90% or more, so far less new damage accumulates every day. |
| Your risk going forward | Yes, it falls. The longer you stay at a high level, the more the total grows. The sooner you stop adding to it, the smaller it stays. |
| Risk from exposure many years ago | Fades, but slowly. In the BEIR VI analysis of miners, exposure more than 25 years in the past carried about half the risk, or less, of recent exposure. |
That last row is a fair thing to know, and it doesn’t make waiting a good plan. The old exposure still counts for something, and every additional year at a high level adds to the pile. The best time to stop adding to it is as early as possible.
Fixing radon stops new damage. It can’t go back and repair the old.
Smoking and radon damage the same cells
Tobacco smoke damages the same airway lining. For a person exposed to 200 Bq/m³ over a lifetime, Health Canada puts lung cancer risk at about 2% for someone who has never smoked and about 17% for someone who smokes. Quitting smoking and lowering radon each reduce the load on those cells, and together they reduce it the most.
What to do
- Test. A long-term test of at least 91 days, ideally between October and April, on the lowest level where you spend more than four hours a day. How to test.
- Fix it if it’s over 200 Bq/m³, and consider it between 100 and 200, where no safe threshold is known. How mitigation works.
- Confirm the fix with a follow-up test, and check the manometer from time to time.
- Don’t smoke indoors, and ask your doctor about lung health and screening if you smoke or used to.
Risk also depends on who is breathing the air and for how long. Radon risk by age covers babies, children, adults and older adults.
Common questions
Can the lungs heal from radon exposure?
Cells repair most DNA damage, but damage that is repaired incorrectly and copied as cells divide stays in those cells. Lowering radon stops new damage and lowers future risk. It doesn’t repair the damage that has already happened.
How long does it take for radon to cause lung cancer?
There’s no fixed time. Radon harm builds over years of exposure, and cancer, when it occurs, usually appears years to decades later. Childhood exposure may not show up until adulthood.
Is there a test to see if radon has already harmed me?
No. There’s no medical test for radon exposure. A radon test of your home tells you the level now. If you’re concerned, especially if you smoke or used to, talk to your doctor about lung health and screening.
If I fix my radon today, is the past exposure forgotten?
It still counts, but it counts for less as the years go by. In studies of miners, exposure more than 25 years earlier carried about half the risk, or less, of recent exposure. Fixing radon stops the total from growing.
Sources
- Health Canada — Radon: Is it in your home? Information for health professionals
- ATSDR (U.S. CDC) — Radon: clinician brief, including exposure in children
- National Research Council — Health Effects of Exposure to Radon (BEIR VI), risk models and time since exposure
- CMAJ (2023) — Radon is responsible for 16% of lung cancer deaths in Canada
- Health Canada — Radon: what you need to know
- World Health Organization — WHO Handbook on Indoor Radon (2009)