Hazardous wildfire pollution is drifting across the American West, creating an unseen health danger that can penetrate far beyond the nose and throat.
Wildfire smoke and fine-particle alerts were active Wednesday in Oregon, Washington, Idaho, Wyoming, Colorado and Nevada.
In multiple communities, air quality deteriorated to unhealthy levels as smoke from fires in the Pacific Northwest and other parts of the West spread through the region.
While some alerts were expected to lift Thursday or Friday, broad areas of Oregon and Washington remained under smoke advisories with no clear end date.
Authorities said changing winds were pushing smoke across state borders, carrying tiny particles through the air and cutting visibility in affected areas.
People in the hardest-hit locations were urged to remain inside, keep windows and doors closed, and limit heavy exertion outdoors.
The greatest concern is fine particulate matter, which is small enough to evade many natural defenses, settle deep in the lungs and, in some cases, move into the bloodstream.
Health officials warn that children, pregnant people, seniors and anyone with asthma, heart disease or other breathing problems are especially vulnerable.
Dangerous toxins are spreading across the American West, bringing an invisible threat capable of reaching deep inside the human body
Wildfire smoke is a complex mixture of gases and particles released when trees, vegetation, buildings and other materials burn.
The greatest threat comes from fine particulate matter known as PM2.5, named because each particle measures no more than 2.5 micrometers across, roughly 30 times smaller than the width of a human hair.
Larger particles are often trapped in the nose or throat, but PM2.5 can travel through the airways and reach the tiny air sacs deep inside the lungs where oxygen passes into the blood.
Some of the smallest particles may cross into circulation, potentially affecting organs beyond the respiratory system.
Short-term exposure can trigger coughing, wheezing, chest tightness, difficulty breathing, headaches and burning eyes, according to the Environmental Protection Agency.
It can also inflame the airways, reduce lung function and worsen asthma, bronchitis and other respiratory diseases.
Particle pollution has additionally been linked to heart attacks, strokes and the worsening of heart failure, particularly among people with existing cardiovascular problems.
In Oregon, advisories stretched across a vast portion of the state, covering communities including Portland, Eugene, Salem, Bend, Sisters, Pendleton, La Grande and The Dalles.
Wildfire-smoke and particulate advisories were in force across Oregon, Washington (pictured), Idaho, Wyoming, Colorado and Nevada on Wednesday
Eastern Douglas County, including areas near Roseburg, was under an advisory until further notice because smoke from the Castle Fire and other blazes was expected to linger.
Baker, Harney and Malheur counties were warned of high concentrations of smoke particles through noon Thursday.
Officials urged residents there to remain inside when possible, keep windows and doors closed and use high-efficiency particulate air filters.
Washington warnings included King, Pierce, Snohomish, Kitsap, Mason, Grays Harbor and Thurston counties, where air quality was expected to range from unhealthy for sensitive groups to unhealthy for everyone.
That alert, which included Seattle and several surrounding communities, was scheduled to remain in force until 5pm Thursday.
Other advisories covered Clark County, including Vancouver, as well as Cowlitz, Skamania and Wahkiakum counties.
Large parts of central and eastern Washington, including Yakima, Walla Walla, Richland, Kennewick and Ellensburg, were under alerts until further notice.
Officials warned that the smoke could cause burning eyes and runny noses while aggravating heart, lung and other serious medical problems.
Idaho’s alerts covered numerous counties, including Ada, Boise, Canyon, Elmore, Gem, Owyhee, Payette, Valley and Washington, where the Air Quality Index was forecast to reach ‘Unhealthy.’
Officials warned that the smoke could cause burning eyes and runny noses while aggravating heart, lung and other serious medical problem. Pictured is Spokane, Washington shrouded in wildfire smoke
Officials warned that everyone could begin experiencing health effects, with vulnerable groups at risk of more serious symptoms.
Residents were advised to avoid extended or strenuous outdoor activity, while open burning was prohibited.
Much of Wyoming was also placed under an alert as smoke from western wildfires spread across the state.
Warnings covered central, western, southeastern and northeastern Wyoming, including Casper, Cheyenne, Laramie, Jackson, Cody, Rock Springs, Sheridan and Gillette.
The Wyoming Department of Health told everyone to avoid prolonged exposure, while urging children, older adults and people with respiratory problems to minimize outdoor activity.
Colorado officials warned of moderate to heavy smoke across dozens of counties, including areas around Aspen, Breckenridge, Colorado Springs, Durango, Grand Junction, Pueblo and Steamboat Springs.
Residents were told to consider temporarily relocating if smoke entered their homes and began making them ill.
Officials said that if visibility fell below five miles because of smoke, pollution had reached unhealthy levels.
An action day was also declared along Colorado’s Front Range, where sunshine, warm temperatures and wildfire smoke were expected to drive up both ozone and fine-particle pollution.
In Nevada, southwest Elko County faced an air-quality action day as particulate levels were forecast to become unhealthy for sensitive groups.
Because smoke concentrations can shift quickly with fire activity and changing winds, officials urged residents across the affected region to monitor local air-quality readings before venturing outside.
