Wildfires ravaging western US spread to 11 states as previously safe areas face new warnings - and horrifying scale of dementia risk starts to emerge

As millions across the West battle blazes amid dangerously high temperatures, a new study has found a connection between long-term wildfire smoke exposure and brain health.

The Park Fire has grown into California's fifth largest wildfire, burning through 389,791 acres across Butte, Plumas, Shasta and Tehama counties with only 18 percent contained as of Wednesday morning, according to CalFire.

Firefighters were battling 95 large fires on Wednesday, most of which were spread throughout the western United States, the National Interagency Fire Center reported.

The National Weather Forecast predicts temperatures will be in the 90s for the Pacific Northwest, northern Rockies and northern High Plains, and in the 100s over much of the northern Great Basin - making it even more challenging to put out the flames.

'The weather is expected to become much warmer and drier later this week, with some winds and potential for thunderstorms. High temperatures, low relative humidity dropping into the teens, and poor nighttime moisture recoveries will allow for increased fire activity and extreme fire behavior,' CalFire said.

'Fire crews are providing structure defense where needed. They are attempting to complete containment lines in some areas and gain a stronghold in the challenging topography while also engaging in mop-up where applicable.'

There have been at least 277 destroyed structures and 29 damaged structures across Butte and Tehama county from the Park Fire.

Over 5,000 fire personnel are battling the blaze that was allegedly started by a man who pushed his burning car into a gulley in upper Bidwell Park near the city of Chico last week.

Ronnie Stout II, 42, has been arrested and charged with arson in connection to the fire.

California's Air Resources Board has deemed wildfire smoke as a 'serious health risk.'

New research has found a link between long-term exposure to wildfire smoke and brain health, CNN reported. 

Researchers measured the impact of PM2.5 - air pollution particles that are 2.5 microns or smaller in diameter - on over 1.2 million people 60 or older in Southern California from 2009 to 2019.

They found the odds of someone exposed to wildfire smoke being diagnosed with dementia rose 21 percent for every increase of 1 microgram of PM2.5 concentration per cubic meter of air over a three-year average. 

'There is quite a bit of prior literature that demonstrates an association between exposure to ambient air pollution and dementia, but there's very limited research on how wildfire PM2.5, specifically, might be associated with dementia,' researcher Dr Holly Elser, an epidemiologist and resident physician in neurology at the University of Pennsylvania, told CNN.

'As wildfire events become more intense, more frequent, and occur in places outside of the Western US, we felt this was an important, specific source of air pollution to consider as a potential risk factor for dementia.'

In Oregon, the state's largest wildfire, the Durkee Fire, has sizzled through 293,882 acres and was 52 percent contained as of Wednesday morning.

Three fires - Alexander Mountain fire, Quarry fire and Stone Canyon fire - are blazing through Colorado.

The Alexander Mountain Fire, which began on Monday in Larimer County, has reached an estimated at 5,080 acres with zero containment by Tuesday, according to the Larimer County Sheriff's Office.

The Chair of the Larimer County Board of Commissioners declared a disaster emergency for the county.

The Stone Canyon Fire has burned 1,320 acres with no significant growth overnight and an evacuation order for parts of Lyons has been lifted.

The Quarry Fire in Jefferson County broke out overnight and has grown to 130 acres with five subdivisions under mandatory evacuation, The Denver Gazette reported.