Last week the smoke from wildfires in the Western US crossed the country. While the air has cleared in some areas, fires continue to burn. And seeing as nasty wildfire seasons are becoming our new normal, it’s unfortunately always a good time to talk about smoke. So I am going to give you this lowdown: what it is, what it does to us, and what you can do to protect yourself when it gets smoky. The smoke that billows off of a wildfire is actually composed of lots of different things.

In fact, those airborne particles are the main reason smoke is visible; if your view is hazy or the sky is a weird colour, you can blame the particles. But we don’t judge how bad the air is just by looking at the sky. Many governments use a measure called Air Quality Index or AQI, which is usually a colour-coded scale of some sort.

In the US, the AQI goes from 0 to 500 and six different ranges.

Each pollutant gets measured separately; a value of 100 corresponds to the level that’s considered okay for short term exposure by the National Ambient Air Quality Standards. Then, the highest of these is what’s reported.

So AQI reflects whatever is most harmful at the time and with smoke that’s usually that PM, especially small bits less than 2.5 microns in size. Starting at an AQI of 151, anyone exposed to the air may be harmed, even people who are otherwise healthy. Common reactions to smoke exposure include:

• Stinging eyes
• Scratchy throat
• Coughing
• Wheezing
• Chest pain
• Tiredness

The good news is that these effects tend to be short-lived. People generally get better when air quality improves. That said, there is a possibility for longer-term harm. And that’s because smoke contains a lot of nasty things. But what’s most likely to cause health problems across the country are those floating, microscopic particles, which can contain some really harmful stuff.

Essentially your immune system launches an assault on the foreign material, and in the process, ends up harming your lung tissues.

This is why people with conditions like asthma, COPD, and heart disease should be especially careful about smoke exposure; the added inflammation can exacerbate what they’re already dealing with. And studies have tied wildfire smoke to things like increases in mortality and decreases in birth weights, though more research is needed. Oh, and, not to freak anyone out, but smoke exposure has also been tied to infectious disease spread later on. Which isn’t great at the current moment. Though, a review from 2016 called this evidence “inconsistent”. So, the jury is somewhat out on that front. Still, between the possibility of that and long-term health effects, it’s probably a good idea to limit exposure.

And beyond keeping indoors there are a few things that health and safety agencies recommend for that.

Like wearing a mask if you have to go out for prolonged periods though you’ll need a full-on N95 or similar to have it make much of an impact. You can also boost the air filtration in your home, to combat anything that makes it inside.

If you have a central heating and cooling system, you might make sure that your filter is up to the task. Specifically, you will want to consider the filter’s Minimum Efficiency Reporting Value or MERV rating. With these, higher is better.

And be sure to actually have the system running, even if it’s just on circulate, so that the filter gets the chance to work. There’s also the option of a free-standing air purifier. For these, you will want to have a high MERV or a certified HEPA filter. That means it’s passed a different test that ensures it captures 99.97% particles exactly 0.3 microns in size so it’s super good at filtering smoke, actually. You should also check out something called the “clean air delivery rate” or CADR. This is essentially how quickly the air passes through the unit.

Bigger rooms need bigger CADRs. Some purifiers even list rates for different types of pollutants. Tobacco smoke represents the finest of these, so look at that if you see it. But avoid any filter that says it uses ozone. Remember, ozone’s one of the things AQI looks for it’s actually an irritant in its own right!

You can even DIY a purifier in a pinch by connecting a high-MERV filter to a box fan!

Finally, once you’ve made a clean space, it’s probably a good idea not to spoil it. So, you may want to avoid things that add to airborne particles, like:

• Lighting candles
• Smoking
• Using gas stoves
• Frying food

And that’s the quick and dirty…or, hopefully, quick and clean… on wildfire smoke. We hope it helps you breathe a little easier.