As summer kicks off and the days grow longer, many people are eager to head outdoors. But for a growing number of people, the start of summer also means there is a greater possibility of smoke in the air. This summer, smoke from wildfires in Canada caused hazy skies and air quality alerts across much of the Midwest and Northeast – the latest reminder of the growing health threats posed by wildfires. And states across the country, including North Carolina, New Jersey and California, experienced ‘out of wildfire season’ activity that prompted air quality alerts. Wildfires are becoming more frequent and more severe. And more people are experiencing smoke exposure than ever before. One of the key findings from this year’s “State of the Air” report was that wildfires are worsening air quality across the U.S., putting more people’s health at risk. The report looked at levels of particle pollution (aka “soot”) and ground-level ozone pollution (aka “smog”) across the country. Here, we take a deeper dive into how wildfires are increasing levels of both particle and ozone pollution, what this means for your health, and what you can do to protect yourself and your loved ones.
What’s in Wildfire Smoke?
Wildfire smoke contains a complex mixture of pollutants, including particle pollution, volatile organic compounds (VOCs) and nitrogen oxides that are harmful to health. Fine particles are the principal health threat in wildfire smoke. These particles are smaller than the diameter of a human hair and can penetrate deep into the lungs. VOCs and nitrogen oxides, when mixed with sunlight, can form ozone pollution, which is a powerful lung irritant (Figure 1).
Health Effects of Smoke Exposure
Exposure to smoke can have a range of adverse health effects, including worsening asthma, COPD and other lung diseases, reduced lung function, bronchitis, increased risk of heart attack and stroke, adverse pregnancy and birth outcomes, and premature death. It can also increase the risk of emergency room visits and hospital admissions. Everyone’s health is at risk from wildfire smoke, but some people face elevated risk, including children, older adults, people who are pregnant and their fetuses, people who live or work outdoors, people with lower incomes, and people living with asthma, COPD or other chronic diseases.
Worsening Particle Pollution
This year’s “State of the Air” report found that wildfires are contributing to worsening levels of particle pollution, exposing more people to this deadly pollutant. For example, in 2023, Western states saw some improvements in particle pollution levels. But smoke from wildfires in Canada drove levels of pollution in Central and Eastern states higher than they have been in many years (Figure 2). For the seventh straight year, the number of people living with failing grades for daily particulate matter increased.
Wildfires are not only increasing the number of days and places with unhealthy spikes of particle pollution, but also the severity of the pollution. This year’s report saw the highest number of red and purple days on the Air Quality Index for daily particle pollution ever in the history of the report (Figure 3). There were over 1200 red “unhealthy” days and 231 purple “very unhealthy” days around the country. There were also 27 code maroon (or “hazardous”) days, the most severe air quality category.
Wildfire smoke from Canada also worsened annual particle pollution levels in a band of states from North Dakota, south and east as far as Maryland. Ten states saw the year-round average for fine particle pollution get worse in every one of their counties monitored for this pollutant.
Reversing Progress on Ozone Pollution
After years of reductions in ozone pollution in many parts of the country, the results in “State of the Air” 2025 marked a distressing reversal of that progress. This year’s report found that more than 125 million people live in counties with F grades for ozone smog (Figure 4). This is an increase of 24.6 million people over last year’s figure.
The hardest hit region of the country for increases in ozone pollution was the Central U.S. (Figure 5). In the North, smoke from wildfires in Canada generated ozone-forming pollutants. And in the South, high temperatures combined with other sources of air pollution created conditions for ozone to form.
We saw record-high numbers of unhealthy ozone days, driven by wildfire smoke and extreme heat (Figure 6). The bottom line is that a changing climate is making catastrophic wildfire smoke events more likely, putting more people’s health at risk and threatening to erode hard-fought clean air progress.
What You Can Do
Before a wildfire, you can plan ahead by creating an evacuation plan, a clean air plan and an awareness plan. Things as simple as checking daily air pollution forecasts at airnow.gov or checking the Fire and Smoke Map at fire.airnow.gov can help you stay prepared and know when to take action.
Identify if you, or anyone in your household, are in a sensitive group. These people need to take additional steps to protect their health. If you are living with chronic lung or heart disease, diabetes, work or live outdoors, are under 18 or over 65 years of age, or are pregnant, you are part of a group sensitive to wildfire smoke.
If you are in an area experiencing poor air quality due to wildfire smoke, actions such as staying indoors, protecting the air in your home and knowing when to seek medical care can help keep you safe. After a wildfire, it’s important to use personal protective equipment and avoid cleanup activities if you are in a sensitive group. For more information on how you can protect your health from wildfire smoke, visit lung.org/wildfire.
You can also advocate for change at the federal, state and local level to help mitigate the harmful impacts of smoke. Sharing your story with decisionmakers is powerful – whether it’s a time you had asthma symptoms on a smoky day or your child spent days indoors because of wildfire smoke. From individuals to federal lawmakers, everyone can play a part in addressing the growing health threats posed by wildfires. See how you can take action at lung.org/take-action.
Blog last updated: July 9, 2025
