Hazardous levels of smoke built up Thursday afternoon from the Camp Fire in Butte County, causing many places in the Sacramento Valley to reach levels well into the hazardous range for several hours.

ABC10 spoke with an expert who explained why the smoke is so hazardous to health:

  • The Camp Fire is still burning.
  • Wind pattern - There is no strong wind pattern to move the smoke out of the region.
  • Inversion - This is when warmer air sits above cooler air and is similar to our winter fog pattern. The foothills are slightly warmer than the valley floor at night. That warmer air above the valley is basically like putting a blanket over us and the air can’t move.

Until one of those elements start to improve, the smoke is here to stay. The concern level is so high, that some school districts will close on Friday.

RELATED: Here's what Sacramento-area schools are closed on Friday, Nov. 16

Dr. John Balmes, a professor of environmental health sciences at the University of California, explained the effects of prolonged exposure to the unhealthy air.

The people most at risk are those with upper respiratory conditions and children under the age of 10.

"Exposure to wildfire smoke can lead to a number of different health issues," he said. "Pneumonia, coughing, and in some cases bronchitis, headaches, moodiness, stress and with limited outdoor access it can cause kids to act out."

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Dr. Balmes also stressed that we have now entered the cold and flu season. That, combined with the wildfire smoke in our the county, adds to the importance of staying indoors as often as possible.


RELATED: "California Wildfires: The New Normal" is ABC10's new 9-part series on how wildfires are changing lives across Northern California.

Watch Now: Episode 7: "Fighting to Rebuild." Even with insurance, the road to recovery from losing everything to a wildfire can be a long one. Over a year later, residents of the Coffey Park neighborhood in Santa Rosa are still fighting to rebuild their lives.