Short version: there is no radon level that's proven completely safe. Radon risk is a sliding scale — the more you breathe in over the years, the higher your risk. But you still need real numbers to act on, so let's talk about what the guidelines say and what your result actually means.
First, what is radon?
Radon is a natural radioactive gas. It comes from uranium breaking down in soil and rock, seeps up through the ground, and gets into homes through the foundation. You can't see it, smell it, or taste it. Outdoors it scatters into the open air and is harmless. Trapped inside a sealed-up house, especially through a long Canadian winter, it can build up.
Why care? Radon is the number one cause of lung cancer in Canadians who don't smoke, and the second leading cause overall after smoking. That's Health Canada's own finding. It isn't fear-mongering, it's the reason the guideline exists.
How does radon actually harm you?
Radon itself is a gas you breathe in and mostly breathe back out. The problem is what it breaks down into. As radon decays it forms tiny radioactive particles that stick to the dust in the air. Breathe those in, and they lodge in your lungs and give off small bursts of radiation over time. Year after year, that damage adds up and can lead to lung cancer.
This is why time matters as much as the number. A moderate level over decades can do more harm than a high level you fix quickly. It's also why the risk is far greater for smokers, since smoking and radon damage the same lung tissue and multiply each other's effect.
Is there a “safe” radon level?
Not really. Health agencies are clear that the risk is continuous. It rises as the level rises, and there's no sharp line below which radon does nothing at all. So no honest company will tell you a reading is perfectly “safe.”
What we do have are action levels: numbers where the risk is high enough that you should fix it. Those are the guidelines to know.
The two numbers that matter: 200 and 100
Health Canada's action level is 200 Bq/m³. If your home tests at or above that, you should mitigate. The World Health Organization recommends acting at 100 Bq/m³, a lower and more cautious bar. Bq/m³ means becquerels per cubic metre, the standard unit for radon in air.
So the two reference points are 200, Canada's action level, and 100, the WHO's recommended level. Neither is a safe-or-unsafe switch. They're the points where the experts say the benefit of fixing clearly beats the cost of leaving it.
It helps to know why the two numbers differ. Health Canada set 200 as a practical action level for Canadian homes, balancing health risk against what's reasonable to ask of homeowners. The WHO looked at similar science and landed on a more cautious 100, arguing that lower is safer and worth aiming for. Both agree on the direction of travel: the less radon you breathe, the better. Neither treats its number as a hard line where danger switches on.
How to read your result
Your test gives you a number in Bq/m³. Here's a plain way to think about where you land.
Below 100 Bq/m³
You're under both guidelines. Good. Radon isn't zero anywhere, so many people still re-test every few years, but there's no action to take right now.
100 to 200 Bq/m³
You're above the WHO's recommended level but below Health Canada's action level. This is a judgment call. Health Canada doesn't require action here, but many families choose to mitigate anyway, especially with young kids in the home or if someone smokes, since the risks stack.
200 Bq/m³ and above
You're at or above Health Canada's action level. You should mitigate. The higher the number, the sooner. Health Canada suggests fixing within about two years at moderate levels, and within a year if you're well above the line, say past 600 Bq/m³.
One thing every level shares: the number is your home's, not your neighbour's. Radon varies house to house because it depends on your specific soil, foundation, and how your home is sealed. A reading two doors down tells you nothing about yours.
Does a low reading mean you're done forever?
Not quite. A single test is a strong signal, but homes change. A renovation, a new basement finish, a fresh crack in the slab, or a different way of heating the house can all shift your radon level over time. If your first result was low, re-testing every two to five years, or after any major foundation work, is a smart habit. If it was borderline, test again sooner to be sure.
And if you're ever comparing two results — say a quick short-term test against a longer one — trust the long-term number. It reflects what you actually breathe across the seasons, not one unusual week.
A few things that are simply not true
- “New homes are safe.” New, energy-efficient homes are sealed tighter, which can trap radon just as easily as an old home — sometimes more.
- “My neighbour tested fine, so I'm fine.” Radon changes house to house. Their result tells you nothing about yours.
- “I'd smell it or feel sick.” Radon has no smell and causes no short-term symptoms at all. A test is the only way to know.
What to do next
If you haven't tested yet, that's step one — read our radon testing guide to do it right. If you already have a high number, the fix is a mitigation system, and you can see what that costs in our radon mitigation cost guide.
Where you live also shifts the odds, because some regions run higher than others thanks to the geology — see Canada's radon hotspots. You can check the general risk picture for your area on a local map, like the Ottawa radon map or the Regina radon map. Just remember a map shows the area, not your house. Only a test gives you your number.