There's no hard and fast rule here. High AQI (poor air quality) can be from multiple sources, and a mask only helps against fine particles like wildfire smoke, not gases such as ozone. But for smoke, a well-fitted N95 is worth it when air moves into the Unhealthy range (AQI 151+). Moving indoors and reducing activity are safest, but a mask can help for those times you have to be outside.
No official AQI tells you to put on a mask outdoors. No health agency sets a mask-on number. What a mask can do depends on what's dirtying the air, and it helps most in one situation: when fine-particle pollution is high, which usually means wildfire smoke. In those situations, a well-sealed N95 mask can cut how much of those fine particles you breathe in by at least tenfold.1 But, the same mask does nothing for the gases in polluted air12. That's the catch on a smoggy summer day, when the problem is ground-level ozone, a gas. A mask won't touch it.
If smoke is the problem, the mask still has to fit. Protection comes from the seal against your face, not the filter rating, so leaks around the edges matter more than whether it's an N95 or something like a P100.3 If you don't have an N95, surgical or one-strap masks give some protection, but not nearly as much, so get an N95 if you can. 34
Ultimately, save the mask for the right moment. Masks are meant for short stretches of unavoidable time outdoors in smoky air5, not all-day wear. Reach for a well-fitted N95 when smoke pushes the air into the Unhealthy range, around AQI 151 and up, and only for short, unavoidable trips outside. Cut back, reschedule, or move indoors first, and never expect a mask to help against smog or ozone.
Sources
- [1] NIOSH / CDC. How to Protect Workers and the Public from Wildfire Smoke (NIOSH Science Bulletin). January 2025. Accessed August 6, 2026. https://www.cdc.gov/niosh/bulletin/2025/wildfire-smoke.html
- [2] NIOSH / CDC. Understanding Filtration Efficiency Testing and Fit Testing in Filtering Facepiece Respirators (FFRs). November 2021. Accessed August 6, 2026. https://www.cdc.gov/niosh/docs/2021-123/pdfs/2021-123revised112021.pdf
- [3] U.S. EPA / USFS / CDC / CAPCOA / NPS / CARB. Wildfire Smoke: A Guide for Public Health Officials (Revised 2026). June 2026. Accessed August 6, 2026. https://www.epa.gov/system/files/documents/2026-06/wildfire-guide-for-public-health-officials-2026.pdf
- [4] GeoHealth 2021;5(9):e2021GH000482 (Kodros JK et al., Colorado State University). Quantifying the Health Benefits of Face Masks and Respirators to Mitigate Exposure to Severe Air Pollution. September 1, 2021. Accessed August 6, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC8438762/
- [5] Annals of the American Thoracic Society (Laumbach RJ). Clearing the Air on Personal Interventions to Reduce Exposure to Wildfire Smoke. July 2019. Accessed August 6, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC6600837/
About the author
Dr. Colin Little
MD, FAWM, Chief Medical Officer, GOES Health
- Board Certified Emergency Physician
- Fellow of the Academy of Wilderness Medicine (FAWM)
- Wilderness Medicine Fellowship, University of Utah
- Emergency Medicine Residency and Chief Resident, Stanford / Kaiser
- Doctor of Medicine, University of Arizona College of Medicine – Phoenix