What You Need to Know About Wildfire Smoke and Its Health Impacts

By Nina Bai

smoke fills the sky from a wildfire

For several years now, wildfires have raged every fall across California. As smoke-filled skies become a regular occurrence, it has raised questions about what people should do to stay safe.

We spoke to John Balmes, MD, a pulmonologist and professor of medicine at UC San Francisco, about the immediate and long-term health risks of wildfire smoke, and what people should be aware of on days with poor air quality.

What’s in the wildfire smoke? What’s the most dangerous?

“Smoke from these catastrophic wildfires is mostly from burning wood and vegetative matter, similar to tobacco smoke but without nicotine,” said Balmes, though he notes that even when the air quality is really bad, it’s still not as bad as inhaling from the end of a cigarette.

When vehicles and buildings burn, the chemicals in the smoke can be more toxic, but these generally make up a small proportion of what is burned and the toxins are diluted considerably as the smoke travels through the air. 

The Air Quality Index (AQI) is a measure of the pollution in the air, generally ranging from zero to 500, and considers the amount of PM2.5 (particulate matter under 2.5 microns) and ozone in the air, among other pollutants. Wildfire smoke adds to the particulate matter in the air, whereas ozone is produced by emissions from cars and power plants reacting with sunlight. An AQI above 150 is considered unhealthy, which means it’s best to stay inside, said Balmes.

Do N95 masks work? Should everyone be wearing them?

N95 masks, which are air-purifying respirators certified by the National Institute for Occupational Safety and Health, are well tested and do work to filter out 95 percent of small particles down to 0.3 microns – but only if they’re properly fitted. “And here’s the rub,” said Balmes. The masks do not fit well on many people.

Health care professionals who wear N95 masks – for example, when dealing with suspected tuberculosis cases – are required to be fit-tested to make sure the masks fit properly, but people wearing them for wildfire smoke probably just use what’s available. The masks come in small, medium, and large sizes, but not all sizes are easy to find commercially.

The masks are designed for beardless, adult faces. “You can’t properly fit-test someone with a beard,” said Balmes. “And they’re not made for kids’ faces, so they’re not officially recommended for kids at all.”

Another problem is that “people get a false sense of protection” and think they are safe to do outdoor activities as long as they are wearing a mask. “You see people jogging with N95 masks,” said Balmes. “That’s the wrong idea.”

Because of these concerns, Balmes said he no longer recommends masks for healthy people. Those with cardiovascular or respiratory disease, such as asthma, can benefit from the masks. “If you have no history of pre-existing disease, wear them if it makes you feel better, but it’s not necessary,” said Balmes.

If you do choose to wear an N95 mask, here is a guide to wearing them properly.

If masks are not the answer, what should children and other vulnerable populations do to stay safe?

If you’re worried about the air quality, it’s best to stay indoors with windows closed and ventilation systems turned to recirculation. Portable HEPA filters work well for cleaning the air for individual rooms and MERV13 filters can be added to central ventilation systems.

“Schools could be a good place for kids if they have relatively modern ventilation,” said Balmes. Newer hospital facilities are generally equipped with good MERV filtration systems.

Of course, filtration is only an option if you have electricity. Balmes, who lives in North Berkeley with his wife, said he put in a MERV filter in their home and bought a portable HEPA filter after last year’s fires, but he was impacted by the Northern California power outages and wasn’t able to use them.

Yearly wildfires seem to have become the new normal for California. What do we know about the health risks of repeated or chronic exposure to wildfire smoke?

A study published in 2018 in the Journal of the American Health Association looked at over a million emergency department (ED) visits during the 2015 wildfires in Northern and Central California. It found that on days with more wildfire smoke, there were more ED visits for numerous cardiovascular disease outcomes, including ischemic heart disease, dysrhythmia, heart failure, pulmonary embolism and stroke, and that the risks were greatest among seniors older than 65.

The study was a collaboration between UCSF, the California Department of Public Health and the U.S. Environmental Protection Agency, and led by Zachary S. Wettstein, MD, who was a UCSF medical student at the time. 

Researchers are just starting to study communities that have been repeatedly exposed to wildfire smoke in the most recent fires, as well as those with higher levels of exposure, such as firefighters.

“Whether repeated exposure over years will cause a problem – we still don’t have that data and it’s going to take years,” said Balmes.

The long-term effects of wildfire smoke on the immune system need more study, but a health consequence that’s well known is an increased risk for respiratory tract infections, said Balmes. The first line of defense in your lungs are alveolar macrophages, amoeba-like immune cells that patrol the airways for contaminants. “If they’re busy eating nasty wood smoke particles, then they’re having a hard time taking care of bacteria and viruses,” said Balmes.

The recent wildfires are a dramatic reminder that climate change not only impacts the environment but has also become a pressing health issue, said Balmes. “We need the public to realize that climate change directly affects health.”