Wildfire Smoke and Your Health: How to Read the Air Quality Health Index and Protect Yourself

The sky has that hazy, orange tint again, and the air smells like a campfire that will not go out. Wildfire smoke is drifting across much of Ontario, and you can feel it: scratchy eyes, a tickle in your throat, maybe a dull headache by the end of the day. On smoky days like these, the most useful thing is not worry. It is a short list of practical steps you can actually take, plus a simple way to check how bad the air is where you live.

This guide walks through what wildfire smoke is, how to read Canada's Air Quality Health Index, the symptoms most people notice, and the concrete things you can do at home to breathe a little easier. Our goal is not to diagnose you or promise that any one step will keep you well. It is to point you to trustworthy public-health resources and help you decide when a symptom is worth a call to a health professional.

What is in wildfire smoke

Wildfire smoke is a moving mixture of gases and tiny particles from burning trees, brush, and everything else in a fire's path. The part that health agencies worry about most is called fine particulate matter, often written as PM2.5. These particles are so small, about 2.5 micrometres across or less, that many of them are far thinner than a human hair.[5]

Size is the whole problem. Because the particles are so fine, you breathe them deep into your lungs, and the smallest ones can even pass into your bloodstream.[5] That is why smoke can leave you feeling unwell all over, not just short of breath. Fine particulate matter is considered the main health concern in wildfire smoke, and there is no level of smoke exposure that is known to be completely safe, so the sensible aim on a smoky day is simply to breathe in as little of it as you reasonably can.[5]

Smoke conditions can also change quickly, sometimes within a single day, as winds shift and fires flare or settle.[5] That is exactly why it helps to have a number you can check rather than guessing from the colour of the sky.

The Air Quality Health Index, and how to check it

Canada uses a tool called the Air Quality Health Index, or AQHI, to turn the day's air quality into a single, easy number. Environment and Climate Change Canada calculates it by combining three common air pollutants, ground-level ozone, nitrogen dioxide, and fine particulate matter (PM2.5), into one reading on a scale that runs from 1 upward.[1]

The scale is grouped into four risk levels:[2]

• 1 to 3 — Low risk. Air quality is good. Most people can enjoy their usual outdoor activities.
• 4 to 6 — Moderate risk. Consider easing up on hard outdoor exertion if you start to notice symptoms like coughing or throat irritation.
• 7 to 10 — High risk. Reduce or reschedule strenuous activities outdoors. People at higher risk, and children and older adults, should take it easier.
• Above 10 — Very high risk. This is the top of the scale. People at higher risk should avoid strenuous outdoor activity, and everyone should consider cutting back or rescheduling it.

During a heavy smoke event, the reading can climb past 10, into the "very high risk" band, which is the index's way of flagging that the air is well outside the normal range.[2]

Checking the AQHI takes less than a minute. In Ontario you can look it up on the Air Quality Ontario website, which posts current readings and forecasts by region, or by phone at 1-800-387-7768 (toll-free) or 416-246-0411 in Toronto.[2] Nationally, Environment and Climate Change Canada publishes local AQHI readings and forecasts on its weather site and in the free WeatherCAN app, so you can see the number for your own community and check the outlook for the hours ahead.[3] It is worth glancing at the forecast, not just the current value, so you can plan errands or a child's outdoor practice around the cleaner parts of the day.

Symptoms most people notice

Even healthy people often feel wildfire smoke. As the amount of fine particulate in the air rises, most people experience some irritation of the eyes, nose, throat, and airways.[5] Common, generally mild symptoms include:

• Stinging, watering, or burning eyes[5]
• A scratchy or sore throat[5]
• Coughing, and sometimes a runny nose or sinus stuffiness[5]
• Headaches[5]

These milder symptoms are unpleasant but usually pass once you get into cleaner air.[5] They are your body's signal that you are breathing more smoke than you should be, and a good prompt to head indoors or put more distance between yourself and the haze.

Smoke can affect more than the body, too. Public-health guidance notes that long or repeated smoky stretches can also wear on mental health, leaving people feeling more stressed or anxious, so it is reasonable to be gentle with yourself during a prolonged event.[5]

How to protect yourself

You cannot control the smoke outside, but you have real influence over how much of it reaches your lungs. The goal of every step below is the same: breathe in less fine particulate.

Ease off on outdoor activity. When the AQHI is high, reduce or reschedule strenuous outdoor activity, especially anything that has you breathing hard, like running or heavy yard work.[2] The harder you breathe, the more smoke you take in. Save the demanding tasks for a day when the number has come back down.

Keep the smoke outside. Indoors is usually cleaner, so keep windows and doors closed when it is smoky out.[6] If your central air conditioner, window unit, or ventilation system has a setting that pulls in fresh air from outside, switch it to "recirculate" or close the fresh-air intake so it is not drawing smoke into the house.[6] Avoid adding to indoor particles while you are sealed in: this is not the day for frying, burning candles, vacuuming without a proper filter, or lighting up indoors.[6]

Filter the air you already have. A portable air cleaner with a HEPA filter can noticeably lower the amount of fine particulate in a room, as long as it is sized for that room.[6] If you have a central forced-air system, a higher-efficiency furnace filter (such as a MERV-13 or higher rating, if your system can handle it) helps capture more of the fine particles as the air circulates.[6] One caution from the U.S. Environmental Protection Agency: skip any "air cleaner" that works by producing ozone, because ozone is itself a lung irritant.[6]

Set up a cleaner-air room. If the smoke lingers for days, it helps to pick one room and make it your cleaner-air space, ideally a room with few windows where the whole household can spend time. Keep its doors and windows closed, avoid anything that makes particles indoors, and, if you can, run a properly sized portable HEPA air cleaner in it. A room set up this way can hold noticeably cleaner air than the rest of the home.[6]

Use a well-fitted respirator if you must be out in it. If you have to spend time outdoors in heavy smoke, a properly fitted, NIOSH-certified N95 respirator (or an equivalent such as a KN95 or KF94) can help reduce how much fine particulate you breathe in.[4] A few things make the difference between real protection and a false sense of it:

• Fit is everything. Choose a size and shape that seals against your face, covers your nose, mouth, and chin, and leaves no gaps around the edges.[4]
• Respirators seal best on clean-shaven skin; facial hair breaks the seal and lets smoky air leak in around the mask.[4]
• Remember what a mask can and cannot do. It targets the fine particles, but it does not filter out the gases in smoke.[4]
• If wearing one feels hard to breathe in, or you have a heart or lung condition that makes it uncomfortable, move to cleaner air before taking it off, and do not wear a respirator while sleeping.[4]

A loose paper or cloth mask, the kind that gaps at the sides, does not seal well enough to give the same protection.[4]

When it is more than everyday irritation

For most people, smoky-day symptoms stay mild and fade with cleaner air. But some people feel wildfire smoke much more strongly. Those at higher risk include people with lung conditions such as asthma or COPD, people with heart conditions, pregnant people, infants and young children, and older adults.[5][7] If that describes you or someone in your home, it is worth being extra careful, checking the AQHI more often, and keeping any regular medicines close at hand. (Our companion piece on who is most at risk from wildfire smoke goes into this in more detail.)

Pay attention if symptoms move beyond mild irritation. Reach out to a health professional, such as your doctor, a nurse line, or your pharmacist, if your symptoms are more than mild, if they will not settle, or if you have a chronic heart or lung condition and are unsure how to manage it during a smoke event.[5] Environment and Climate Change Canada and Health Canada also publish plain-language resources on wildfire smoke and air quality that are worth keeping bookmarked for the season.[3][5]

Some signs need help right away. If you or someone with you has severe trouble breathing, chest pain or tightness, a fast or irregular heartbeat, severe dizziness, fainting, or confusion, treat it as an emergency and call 911.[5] Do not wait to see if it passes.

The bottom line

Wildfire smoke is a normal reason to feel off on a hazy day, and it is also something you can take practical steps against. Check the AQHI before you head out, keep hard outdoor exertion for cleaner hours, close up and filter your indoor air, set aside a cleaner-air room if the smoke settles in, and reach for a well-fitted N95 only when you truly must be out in it. Know who in your household needs extra care, know when a symptom deserves a call to a health professional, and know that 911 is the right move if breathing becomes an emergency. None of this makes the smoke disappear, but together these steps put a lot more clean air between you and the haze.

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