Wildfire Smoke Kills Through a Hidden Pathway
Wildfires are more dangerous than they appear. Beyond smoke and soot, the ozone they generate kills people, and that effect has been largely overlooked until now.
When forests and vegetation burn, they release not only fine particles and soot but also chemical compounds that react with sunlight in the atmosphere to form ozone (O₃). Ground-level ozone (distinct from the protective ozone layer high in the stratosphere) is harmful to the lungs and cardiovascular system.
The study, published in Science, quantifies for the first time how large the contribution of wildfire-derived ozone is to total mortality. The conclusion is uncomfortable: the effect is substantial and falls outside the standard models governments use to estimate the health impact of wildfires.
Chronic exposure and ageing
Ozone exposure is not only acutely dangerous. Long-term exposure to elevated ozone accelerates lung ageing, raises the risk of chronic lung disease and increases cardiovascular risk. The underlying mechanism is oxidative stress, which refers to cellular damage caused by reactive oxygen compounds. That is precisely the process that also plays a central role in biological ageing more broadly.
As the climate changes, wildfires are becoming more frequent and more intense. That means more people, including those far from the fire itself, are exposed to elevated ozone levels. Urban areas downwind of fire regions are particularly vulnerable, because ozone travels over long distances.
A blind spot in health policy
The research has direct policy implications. Air quality models that ignore wildfire ozone underestimate health damage. Older adults and people with existing lung or heart conditions are most at risk. From a longevity perspective, this is an external factor that affects late-life health and largely lies beyond individual control. That makes it a collective and political problem, not merely a medical one.