You’ve probably seen AQI numbers pop up on your weather app during wildfire season and wondered if it actually matters. It does.
AQI stands for Air Quality Index. It’s a scale that measures how polluted the air is on any given day. The higher the number, the worse the air — and the more your body has to deal with.
Wildfire smoke is full of tiny particles called PM2.5 — fine particles so small they slip right past your nose and throat and go deep into your lungs. According to AirNow.gov, these fine particles can aggravate chronic heart and lung diseases and are even linked to early deaths in people with those conditions. Even if you’re totally healthy, breathing smoke is still worth avoiding when you can.
So when should you actually go inside?
Here’s how the AQI zones break down:
– 0–50 (Green): Good. Air quality is satisfactory.
– 51–100 (Yellow): Moderate. Unusually sensitive people may want to limit prolonged outdoor exertion.
– 101–150 (Orange): Unhealthy for Sensitive Groups. People with asthma, heart conditions, or lung disease should reduce outdoor activity.
– 151–200 (Red): Unhealthy for Everyone. The California Air Resources Board says children and other sensitive groups should stay indoors with windows and doors closed once AQI hits this level.
– 201+ (Purple or Maroon): Very Unhealthy or Hazardous. Yale Medicine notes that when AQI climbs to 201 or higher, everyone — not just sensitive groups — should be worried and limit outdoor physical activity as much as possible. For reference, during the worst days of the 2023 Canadian wildfires, PM2.5 AQI pushed well above that level in parts of the U.S.
And going inside isn’t just about comfort. The EPA points out that reducing smoke exposure matters for everyone’s health, especially kids, older adults, and anyone with heart or lung issues. If local officials tell you to stay indoors, they mean it — close your windows, seal gaps if you can, and try to keep the indoor air as clean as possible.
The honest bottom line: if you’re young and healthy, a brief exposure to moderately smoky air probably won’t wreck you. But “probably fine” isn’t the same as “no risk,” and there’s zero upside to sucking in smoke when you don’t have to. When the AQI is climbing into the red (151+), stay inside, skip the outdoor workout, and keep the windows shut.