A shift in the winds late Friday brought thick smoke from wildfires burning in Washington to cities on the west side of the Cascades.

The smoke caused harmful air quality for residents in Southwest Washington and the Willamette Valley.

“The air quality has gone from moderately bad, to unsafe for certain people, to unhealthy overall,” said Dr. Paul Lewis, the Tri-county health officer. “It’s really about the worst air pollution event that I can remember in the Portland metro area.”

More than 1 million acres are burning in Oregon and Washington, as wildfires continue to grow around the Northwest.

Mandatory evacuation orders are still in place for many residents in north-central Washington state. Throughout the region, hundreds of homes and other structures have burned. But slightly cooler weather Saturday aided the more than 9,000 wildland firefighters who are on the ground in the two states.

The haze caused by those fires was so thick in Portland Saturday afternoon, it was difficult to see downtown skyscrapers from the east side of the Willamette River.

The smoke did not disrupt flights in and out of Portland International Airport.

But Portland had among the worst air-quality of any major city in the country, Dr. Lewis said.

The concern with poor air quality, he said, is the nose and mouth don’t filter the tiny particles in the smoky air. That means they get lower in the lungs, he said.

“Your lungs don’t like having things down in there,” he said. “It affects everybody, but those with more sensitive conditions are more likely to feel the symptoms.”

Those with sensitive lungs might start to cough, and potentially go into a cycle where it gets harder for them to breathe, he said.

Lewis said eventually, cells in a person’s immune system can clean up the tiny smoke particles.

“In the long run, the little Pacmen in your lungs chew them up, and either get rid of them, or you cough them up and swallow them,” he said.

Lewis encouraged everyone to use common sense and limit the amount of time they spend outside.

Gerald Macke with the National Weather Service said the smoky air in around the region is expected to start clearing late Sunday and into Monday.

“It’s going to take awhile for this thing to clear up,” Macke said. “The smoke has extended all the way to the coast and we see on the satellites that it’s going 100-plus miles out into the Pacific.”

Smoke from wildfires is more typical for Oregonians and Washingtonians living east of the Cascades. But that’s not so much the case for Salem, Vancouver and the Portland metro area.

“We’re sort of not used to it really,” Macke said. “It’s just not something that we’re experienced with.”

As for the fires, they continue to grow around the Northwest. But a break is on the horizon, said Katie Santini, a spokeswoman with the Northwest Interagency Coordination Center.

“We have had a little bit of relief in the weather,” she said. “Things have cooled down a little bit. The winds are expected to drop off for the next couple of days.”