Do N95 masks protect you from wildfire smoke?

Of everything in wildfire smoke, the fine particles called PM2.5 matter most to your health. They're tiny; a human hair is about thirty times thicker than the biggest of them. Some travel deep into your lungs, and a few may even reach your bloodstream. Most healthy people recover quickly from breathing smoke, though children, older adults, pregnant women and people with heart or lung disease face greater risk. Worn correctly, an N95 sharply cuts how many of those particles you breathe in. A surgical or one-strap mask protects less, and a cloth covering or bandana shouldn't be counted on for smoke protection.

The filter's fibers hold a static charge that grabs particles from the air as it passes through. The 95 comes from a deliberately harsh test: NIOSH picks the particle size hardest to catch, about 0.3 microns, and the material has to stop at least 95 percent of them as you breathe in. But that number only counts the air going through the filter. Fit decides everything. Air takes the easiest path it can find, so any gap in the face seal lets smoke slip past the filter and cut your protection.

A beard where the mask meets your face makes a tight seal impossible, though shorter stubble may still leave you some protection. If you have heart or lung disease, check with your health care provider before using one. A respirator makes breathing harder, and it can raise your risk of heat illness when you're active or the weather is hot. If it leaves you dizzy, faint or struggling for breath, take it off and get to cleaner air.

An N95 filters particles, not gases. For anyone well away from a fire, the carbon monoxide in wildfire smoke usually poses no real hazard to health. Close to the flames, it can become an immediate danger. And if you're that close, a mask is beside the point: get to safety and call for help. Farther out, where drifting smoke is the problem, those fine particles are the whole concern, and a well-fitted N95 handles them. Even then, a mask is only a backstop. The most effective step is to stay indoors and limit your time in the smoke, and running a portable air cleaner indoors cuts the smoke particles you breathe there.