(KDVR) — With smoke from over 400 Canadian wildfires drifting south and blanketing much of the U.S., Americans are looking for ways to cope with a haze of very unhealthy air.

Dr. Anthony Gerber said the people most at risk in smoky conditions are those with lung disease, older people, and the very young. He said if those people have symptoms outside, they may benefit from wearing a well-fitted mask.

But keep in mind, surgical and cloth masks do not help in these conditions.

“Really, N95s are the only masks which are really proven to be effective,” Gerber said.

N95 masks filter particles as small as 0.3 micrometers, a fraction of the width of a human hair, according to the California Department of Public Health.

Still, masks are not an ideal solution for wildfire smoke. San Francisco health officials previously told SF Gate that sealed buildings with filtered HVAC systems are preferable to mask use.

“If you have filters on your home HVAC system, you should make sure they’re up to date and high quality,” Dr. David Hill, a pulmonologist in Waterbury, Connecticut told the Associated Press.

Air quality alerts often caution “sensitive groups,” to stay indoors. That is a big category that includes children whose lungs are still developing, older adults, and people with lung diseases, such as asthma and chronic obstructive pulmonary disease.

Gerber, a pulmonologist at National Jewish Health, said filters can help with smoke, but not all are effective, “Most folks will put them in their bedroom, but again, it has to be a HEPA filter and it has to be matched to the size of the space you are filtering.”

Even though smoke seems familiar, it is actually a complex mixture of shapes, from round to corkscrew-shaped under the microscope. It’s an intense form of pollution.

That makes this a good time for everyone to put off yard work and outdoor exercise.

As during the coronavirus pandemic, health officials say a snug fit is the key to getting protection from your N95. Bandanas and surgical masks typically fail to offer the needed protection.

The good news is that weather patterns change and the worst conditions should only last a day or two, though lighter smoke could linger for several days.

The Associated Press contributed to this report.