At what Air Quality Index should someone with asthma stay inside?

For many people with asthma, an Air Quality Index, or AQI, above 100 is the point to start changing outdoor plans. That does not always mean you need to stay inside all day. It does mean outdoor air has reached the range the EPA calls unhealthy for sensitive groups, and people with asthma are one of those groups.

This question is especially timely in June 2026. Summer ozone season is starting in many parts of the United States, and wildfire smoke was already affecting Southern California communities in May. The practical takeaway is simple: once AQI goes above 100, many people with asthma should start cutting back on outdoor exertion. As the number rises, stronger limits make sense.

What the AQI means for asthma

The AQI is a daily score for outdoor air pollution. It tracks several pollutants, but for asthma, two of the most important are ground-level ozone and particle pollution.

Ozone is a lung irritant that often builds up on hot, sunny days, especially later in the day. Particle pollution includes tiny particles from smoke, traffic, industry, and other combustion sources. Both can irritate the airways and trigger coughing, wheezing, chest tightness, and shortness of breath.

The AQI is useful, but it is not a perfect personal rule. Some people with asthma are unusually sensitive and may feel worse even before the AQI reaches 100. Others may not notice symptoms until it is higher. The EPA and CDC still point to AQI above 100 as the main threshold where sensitive groups should begin making changes.

A practical AQI guide for people with asthma

Under 100

For many people, outdoor activity is usually reasonable in this range. But pay attention to how you feel. If your asthma is easily triggered by smog, smoke, heat, or exercise, it is reasonable to scale back sooner, especially if you will be active outside for a long time.

101 to 150

This is the unhealthy for sensitive groups range. For many people with asthma, this is the point to reduce prolonged or heavy outdoor activity. A hard run, intense yard work, a long outdoor practice, or a physically demanding work shift may be more likely to trigger symptoms than a shorter or lighter activity.

If you can, move exercise indoors, shorten the activity, choose a lower-exertion option, or go out when local air quality is better.

151 to 200

This is unhealthy air. People with asthma are more likely to feel the effects here, and even people without lung disease may notice irritation. At this level, many people with asthma should avoid strenuous outdoor activity and keep necessary outdoor time shorter and lighter.

If symptoms start, stop the activity and go indoors.

201 and higher

This is very unhealthy air or worse. For most people with asthma, this is the clearest stay-inside-as-much-as-you-can range. Move exercise, sports, and nonessential outdoor chores indoors or postpone them. If you must go outside, keep the trip brief and watch closely for symptoms.

How to use AQI in real life

AQI works best as a planning tool, not just a number in a weather app.

Exercise: On poor-air days, swap a run or hard bike ride for a shorter walk, an indoor workout, or a time of day when the AQI is lower.
School sports and camp: Children are in a sensitive group. Parents, coaches, and schools should check AQI before outdoor practices, recess, and games.
Outdoor work: People who work outside can get far more exposure than someone running a quick errand. If you have asthma, ask whether duties, pace, or timing can be adjusted on bad-air days.
Commuting and errands: If AQI is high, try to keep outdoor waits and nonessential trips short.

Wildfire smoke and ozone are not the same thing

Wildfire smoke and ozone often overlap in the same season, but they are not identical. Smoke is mainly a particle-pollution problem. Ozone is a gas that forms when sunlight acts on other pollutants. During hot, smoky periods, both can matter for asthma.

The American Lung Association’s 2026 State of the Air report says climate conditions and worsening wildfire smoke can make ozone problems harder to control in some parts of the country. That helps explain why summer can be especially rough for people with asthma, even far from a fire itself.

Who may need extra caution

People with asthma are already part of a sensitive group, but some people may need to be even more careful: children, older adults, people who exercise outdoors, outdoor workers, and communities that face repeated smoke exposure or other heavy pollution burdens. If your asthma is not well controlled, your margin for error may be smaller.

When symptoms mean stop, call, or get emergency help

If bad air is making you cough, wheeze, feel chest tightness, or feel short of breath, stop the activity and go indoors. Follow your asthma action plan and use quick-relief medicine only as prescribed for you.

Contact a clinician promptly if symptoms are harder to control than usual, if poor-air days keep triggering problems, if you are short of breath while talking, or if you are needing your quick-relief medicine more often than usual.

Go to the emergency room or call 911 right away for warning signs such as severe shortness of breath at rest, extreme trouble breathing, bluish lips or face, confusion, severe drowsiness, or severe chest pain.

What is known and what is still uncertain

What is known: ozone and particle pollution can worsen asthma, and AQI is a useful way to decide when to scale back outdoor activity. What is less certain is the exact number at which any one person will react. AQI measures outdoor air, not your exact personal exposure, and local conditions can change by hour, block, and activity level.

That is why the best rule is part science, part self-awareness: use the AQI to plan ahead, but also trust early symptoms as a sign to stop and get to cleaner air.

What readers can do today

Check the AQI before outdoor exercise, sports, or long stretches outside.
Start modifying outdoor activity once AQI goes above 100.
Be much more cautious at 151 and above, and treat 201 and higher as a strong reason to stay indoors for most nonessential activity.
Keep your asthma medicines with you and review your asthma action plan.
Ask your school, camp, coach, or employer how they handle poor-air days.
If air pollution repeatedly triggers symptoms, bring that pattern to your clinician instead of trying to change treatment on your own.

The bottom line: for many people with asthma, AQI above 100 is the point to start cutting back outside, while AQI 201 and higher is where staying indoors becomes the safer default for most activities.

Sources

Editorial note: Weence articles are researched from cited public-health, medical, regulatory, journal, and reputable news sources and may be drafted with AI assistance. They are checked for source support, clarity, and safety guardrails before publication.

This article is for general informational purposes only and is not medical advice. Research findings can be early or incomplete, and health guidance can change. Always talk with a qualified healthcare professional about personal symptoms, diagnosis, medications, vaccines, screenings, or treatment decisions. If you think you may have a medical emergency, call emergency services right away.