“When this is happening people’s health is suffering,” said Sarah Henderson, senior scientist in environmental health services at the British Columbia Center for Disease Control. “There is no doubt.”

Studies have shown that, when waves of smoke hit, the rate of hospital visits rises and many of the additional patients experience respiratory problems, heart attacks and strokes.

Dr. Henderson said smoke exposure could have lifelong health implications for babies, though she said more research on the question was needed. “This may do damage to the developing lungs that they may never recover from,” she said.

The risks are greater for people of color, who tend to live in areas already exposed to high levels of particulate pollution. According to a 2017 study, older Black people are three times more likely to be hospitalized for respiratory conditions because of smoke.

Francesca Dominici, a professor of biostatistics at Harvard and an author of the study, said, “Underrepresented minorities are experiencing a much higher health burden from pollution and wildfire smoke and, now, Covid.”

The coronavirus pandemic, which has also hit people of color disproportionately, adds further problems. The Centers for Disease Control and Prevention has warned that “people with Covid-19 are at increased risk from wildfire smoke during the pandemic.”

And the health effects of wildfire smoke don’t go away when skies clear. A recent study on Montana residents suggested a long tail for wildfire smoke exposure.

Erin Landguth, an associate professor in the school of public and community health science at the University of Montana and the lead author on the study, said research had shown that “after bad fire seasons, one would expect to see three to five times worse flu seasons” months later. The study’s findings, she added, fit what is already known about pollution and disease.

“Decades of research have shown that elevated air pollution exposure is associated with a number of adverse health impacts, including compromised immune systems,” Dr. Landguth said.

What’s the climate connection?

The underlying causes of the rising fire risks in the American West are complex. They include past forestry practices that created abundant fuel for fires and the expansion of communities up to the edges of forestlands.

Underlying all of that, however, is climate change, which warms and dries out the vegetation fuel so that a spark — whether from downed power lines, lightning or even a gender-reveal party gone terribly wrong — can lead to a vast scorched landscape.

Even with the most aggressive effort to fight global warming, the inherent lag time in the climate system means that worsening fires and their health effects will be with us for decades. With less vigorous action, the effects of warming will become even more disastrous. “Into the climate future, we’re just going to keep seeing situations that set new records,” Dr. Henderson said.

Daniel Swain, a climate scientist with the Institute of the Environment and Sustainability at the University of California, Los Angeles, said that many of today’s fires, even with a measure of containment, “are going to be going for weeks, if not months, and are going to be generating smoke for weeks, if not months.”

Normally, Dr. Swain said, what finally extinguishes the fires are autumn rains and snowfall, which historically come in October or November. However, he added, “recently, it’s been coming later than that,” and climate change, again, appears to be part of the reason.

Can you protect yourself?

The C.D.C. recommends limiting exposure to smoke by staying indoors with windows and doors closed and running air-conditioners in recirculation mode so that outside air isn’t drawn into your home.

Portable air purifiers are also recommended, though, like air-conditioners, they require electricity. If utilities cut off power, as has happened in California, those options are limited.

If you do have power, avoid frying food, which can increase indoor smoke.

Experts say it is especially important to avoid cigarettes. They also recommend avoiding strenuous outdoor activities such as exercising or mowing the lawn when the air is bad. When outside, well-fitted N95 masks are also recommended, though they are in short supply because of the pandemic.

Some do-it-yourself options are available, Dr. Henderson said, noting that masks made from different layers of fabrics, “particularly tightly woven cotton and silk together,” can provide “pretty good filtration” if they are fitted closely to the face.

Asked the best way to protect yourself in an area shrouded in smoke, Dr. Dominici said the question was a difficult one because many people don’t have the ability to move or the luxury of choice about whether to work outside.

But the safest option? “I would just leave,” she said.

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