Smoke from Canadian wildfires is once again blowing into the U.S., and air quality alerts are in place for much of the Midwest and parts of the Northeast.

When smoke fills the sky, there's also plenty of bad advice floating around. Here's what really works, and what doesn't.

Myth: Any mask will protect your lungs

The biggest health threat from wildfire smoke is PM2.5, tiny particles small enough to travel deep into your lungs and even enter your bloodstream. The best protection is a properly fitted N95 respirator. KN95 and FFP2 masks offer similar protection.

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But there's a catch: Even the best mask won't help if it leaks. A good respirator should seal snugly against your face with no gaps around your nose, cheeks or chin.

(MORE: Smoky summer? How El Niño could play a role)

Don't rely on:

• Surgical masks
• Cloth masks
• Dust masks
• Bandanas
• Wet towels or cloths

Myth: Staying inside automatically keeps you safe

To make your home a cleaner-air space:

1. Keep all windows and exterior doors closed.
2. Set your HVAC system to "On" instead of "Auto" and recirculate the air so it isn't constantly pulling smoky outdoor air inside.
3. Install MERV 13 or higher furnace filters if your system can use them.

Myth: Any air purifier works

Only HEPA air cleaners are designed to remove the fine particles found in wildfire smoke. Place them in the rooms where you spend the most time, especially bedrooms and living areas.

Many inexpensive "air purifiers" don't contain HEPA filters and won't effectively remove PM2.5.

(MORE: Here’s what wildfire smoke does to your body)

Myth: If you're not near a wildfire, smoke isn't a concern

Smoke from wildfires can ride weather patterns for days, affecting communities far from the flames. That's exactly what's happening across parts of the West, where smoke from fires in multiple states is combining to create unhealthy air quality.

That's why it's important to check the air quality where you live, not just the wildfire map. Your weather app can tell you when smoke levels become unhealthy.

A simple rule of thumb: If you can't see about five miles into the distance, the air is likely unhealthy. When air quality is poor, limit time outdoors whenever possible, especially if you have asthma, heart disease, are older, pregnant or have young children.