The mucus and hairs in your nose can trap larger particles, and the mucus and cilia in your upper airway can catch some as well, said Luke Montrose, an environmental toxicologist at Colorado State University. But some PM2.5 or smaller particles can bypass these defenses and penetrate the deepest parts of your lungs.
Dr. Montrose described the lungs as an upside-down tree: Smoke travels through your airway, the trunk. The smallest particles can reach the tips of the tree’s leaves, the alveoli. These air sacs deposit oxygen from your breath into your bloodstream. When PM2.5 particles travel into them, it can impair lung function and cause irritation.
Even smaller particles of smoke, ones a thousandth the size of PM2.5 matter, may travel from your lungs into your bloodstream, which can cause damage at the cellular level, said Carlos Gould, an environmental health scientist and assistant professor at the University of California, San Diego. This could explain some of the health effects researchers have linked to wildfire smoke, including heart conditions, infertility and dementia.
Those who are very close to a wildfire could also ingest particles that settle into drinking water or food. Those particles are dangerous to consume, as they can contain potentially cancer-causing substances like benzene. Skin and hair follicles may also absorb smoke, which can cause itching and skin irritation.
Unanswered Questions
Untangling the relationship between health and smoke is challenging. There are huge variations in how healthy people are before smoke exposure, how much smoke they are exposed to and what’s in that smoke.
Two of the biggest questions researchers want to answer: How much time do you need to spend in smoky air to suffer health effects? And how smoky does the air have to be for that to happen?
One metric of wildfire smoke pollution is the air-quality index, which measures five pollutants on a scale of 0 to 500. Generally speaking, A.Q.I. levels over 100 are considered potentially risky for children, older adults and those with heart or lung diseases, and levels over 200 are considered “very unhealthy” for everyone.
Researchers are just beginning to study how different levels of air pollution might affect health by tracking the outcomes of wildfire survivors over time. After a fire in 2017, researchers at the University of Montana looked at members of a community that was exposed to heavy smoke for six weeks and followed them for two years.
Over those six weeks, the average A.Q.I. in the area was about 221. The researchers didn’t see any changes in participants’ lung function at first. “But then, in the next year or so, they started to see that lung function had declined,” Dr. Montrose said.
Research also suggests that these effects could be cumulative, meaning that your risk can increase over time as you face more exposure. People who are frequently exposed to high levels of smoke, like some firefighters, can develop serious problems. Their lung function can decline, and they can develop higher levels of inflammation. They may also have an increased risk of lung cancer.
Researchers don’t have the data to determine whether it is more harmful to experience high levels of smoke for a short period or low levels for a long period, but they are sure of this: As the number of smoky days in the United States increases, many Americans will be at elevated risk as smoke affects them year after year.
“There’s been a shift from looking at kind of daily and weekly level exposures to looking at annual or multiyear exposure, since there are now chronically exposed communities,” said Stephanie Cleland, an environmental health scientist and assistant professor at Simon Fraser University.
How to Protect Yourself
If smoke is in the air, try to stay indoors with your windows shut, she said, especially if you have a chronic condition that puts you at higher risk. Dr. Gould recommended using an air purifier indoors if possible. (You can make one by taping a furnace filter over a box fan.)
It is not always possible to avoid going outside on smoky days. If you must, avoid strenuous exercise and wear an N95 mask.
There aren’t clear answers on when, exactly, you should avoid smoke exposure outdoors, but public health officials often issue health warnings when the A.Q.I. is over 100.
Dr. Cleland recommended that people check air-quality reports during summer and fall, the same way they might check the weather. “People tend to react if they can see, smell or feel smoke,” she said, “but health impacts happen before it reaches that level.”
