How Wildfire Smoke May Affect Brain Health

Smoke from wildfires in Canada swept across parts of the United States at least twice this spring and summer, carrying with it pollution that likely included toxic gases, acids, soot, and metals let off by materials in the fires, including buildings and chemicals.

Hotter temperatures have caused a rise in the number of wildfires in North America and jeopardized people’s health. The consequences aren’t limited to burning eyes and inflamed lungs. Research suggests that wildfire smoke may increase the risk of developing or worsening neurologic disorders such as Parkinson’s and Alzheimer’s diseases.

Wildfire smoke may be harsher than normally polluted air due to its particle size. Known as particulate matter 2.5, they are smaller than 2.5 microns in diameter, or 1/30th the width of a human hair. That’s small enough to pass through nasal passages and reach the olfactory bulb, which sends messages about smell to the brain, says Ray Dorsey, MD, the David M. Levy Professor of Neurology at the University of Rochester in New York and an author of Ending Parkinson’s Disease. “Larger particles can’t pass through nasal hairs,” says Dr. Dorsey.

In addition, when ozone (a gas released in wildfires), is inhaled by the lungs, it may trigger an immune response that damages brain cells and interferes with memory and cognition. Exposure to wildfire smoke early in life may be a risk factor for developing neurologic diseases later in life. Pervasive wildfire smoke is a relatively new phenomenon, so it is only now beginning to be studied.

Research on air pollution suggests an association between poor air quality and cognitive decline, says Dr. Dorsey. In a study published in the journal Environmental Research in 2018, researchers looked at the brains of more than 200 people who had died between the ages of 11 months and 40 years and had lived in Mexico City—well known for its pollution. All but one of the brains showed at least the beginnings of changes that scientists have previously found in the brains of people with Alzheimer’s disease. The researchers also studied nine brains of people who lived in rural areas and breathed cleaner air, and those brains did not have the same changes.

Researchers aren’t sure what causes the changes. The toxins may lead to misfolding of amyloid, a brain protein involved in both Alzheimer’s and Parkinson’s diseases. And in people who have one of those conditions, the particulate matter of wildfires is associated with faster progression of the diseases. A study by researchers at the University of Southern California published in 2017 found that older women who live in places with fine particulate matter exceeding the Environmental Protection Agency’s standard are 81 percent more at risk for cognitive decline and 92 percent more likely to develop dementia, including Alzheimer’s.

Studies also have found an association between wildfire smoke and an increase in visits to the emergency department for stroke and cerebrovascular disease, says Sarah Song, MD, FAAN, associate professor of neurology at Rush University Medical Center in Chicago. People who have high blood pressure and other risk factors for stroke may be at higher risk for cardiovascular and cerebrovascular complications when exposed to wildfire smoke, she says.

Given these risks, it’s important to take the following precautions:

Determine air quality. Download the FEMA app, sign up for real-time alerts from the National Weather Service or your local health department, or type your zip code or city into the U.S. Air Quality Index. For more information on keeping safe from wildfire smoke, contact the American Heart Association, the U.S. Centers for Disease Control and Prevention, or the Department of Homeland Security.

Stay inside. When a public health advisory is in effect, remain indoors as much as possible.

Wear a mask. When outside, cover your mouth and nose with a N95 or KN95 mask.

Shut out bad air. Close windows and doors tightly when inside and turn on the air conditioning (which should have a HEPA filter). If you don’t have AC, try a portable air cleaner with a HEPA filter. Otherwise, use fans to help disperse any particulates in the air.

Keep inside air clean. Avoid frying, broiling, or using a gas stove. Don’t dust or vacuum, and don’t make a fire in the fireplace, light a candle, or smoke—these activities increase indoor pollution, and vacuuming stirs up particles inside the home.

Seek alternative shelter. If your home does not have an air conditioner and it’s too warm to stay inside, contact your local and state agencies to see where you can stay cool. Churches, libraries, and other public spaces are good options.