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What Happens to Your Lungs at Every Air Quality Level

July 16, 2026

Before heading outside, you might check the temperature, chance of rain or whether you’ll need a jacket. But lately, there may be another number competing for your attention: the air quality index, or AQI.

The AQI can rise because of smoke, ground-level ozone, vehicle exhaust and other forms of pollution. And as that number climbs, the air can become harder on your lungs, even when the sky doesn’t look particularly hazy.

“The air quality index helps us understand how likely the outdoor air is to affect our health,” says Mehak Gandhi, MD, with Hartford HealthCare Medical Group. “A higher number means there is more pollution in the air and a greater chance of experiencing respiratory symptoms.”

So, what happens to your lungs as air quality gets worse? Here’s what each level can mean for your breathing.

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The air quality index measures your health risk

The AQI runs from 0 to 500 and is divided into six color-coded levels.

Green represents good air quality. From there, the colors move through yellow, orange, red, purple and maroon as pollution and health concerns increase.

The number is based on several common air pollutants, including particle pollution and ground-level ozone. These are two of the pollutants most likely to affect your lungs.

“The AQI does not measure how much damage has occurred in your lungs,” Dr. Gandhi says. “It tells you how concerning the current air may be and who is most likely to feel its effects.”

Your response can also depend on how long you are outside, how active you are and whether you have an underlying health condition.

Green AQI: 0 to 50 is good

A green AQI falls between 0 and 50 and means the air quality is considered good.

At this level, most people can spend time outside without worrying about air pollution affecting their breathing.

What to do: Enjoy outdoor activities as usual.

Yellow: 51-100 is moderate

Air quality is still considered acceptable on a yellow day.

Most people won’t notice any effects, but someone who is unusually sensitive to pollution may develop mild symptoms.

That could include a cough, throat irritation or feeling slightly more winded during strenuous activity.

“For the average healthy adult, green and yellow days are unlikely to cause a significant breathing problem,” Dr. Gandhi says. “But someone with sensitive airways may notice irritation before other people do.”

What to do: Most people can follow their normal routine, but unusually sensitive people should watch for symptoms.

Orange AQI: 101-150 is unhealthy for sensitive groups

Once the AQI reaches orange, sensitive groups need to be more cautious.

That includes children, older adults and people with asthma, chronic obstructive pulmonary disease or other heart and lung conditions. Pregnant people and people with certain chronic health conditions can also be more vulnerable.

At this level, pollution can irritate the airways and make them more reactive.

“Someone with asthma may begin coughing, wheezing or feeling tightness in the chest on an orange air quality day,” Dr. Gandhi says. “The same exposure might not cause noticeable symptoms in someone without a lung condition.”

Symptoms might be more apparent during a workout, sports practice or physical job because you breathe faster and pull more air into your lungs.

What to do: Sensitive groups should shorten outdoor activities or move them indoors.

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Red AQI: 151 to 200 is unhealthy

Red air quality can begin affecting anyone, not just people with sensitive lungs.

People in higher-risk groups face a greater chance of more serious symptoms.

You may notice:

Coughing or wheezing
Chest tightness
Shortness of breath
Burning in your nose or throat
Less stamina during physical activity

“When air quality reaches the red level, even healthy lungs can become irritated,” Dr. Gandhi says. “The longer or harder you exert yourself outside, the more pollution you may inhale.”

And it’s important to know that the effects are not always immediate. A person may feel fine while outside, then develop a cough, headache or fatigue later in the day.

What to do: Consider limiting prolonged or intense outdoor activity, and watch for symptoms like coughing, wheezing or shortness of breath.

Purple AQI: 201-300 is very unhealthy

Very unhealthy air creates a higher risk of symptoms for everyone.

The airways may become inflamed, making it harder for air to move freely through the lungs.

Symptoms can be more intense for someone with asthma or COPD, and exposure can contribute to a flare that requires additional medication or medical care.

What to do: Move exercise and other strenuous activities indoors and reduce time outside.

Maroon AQI: 201-300 is hazardous

At the maroon level, air quality is considered hazardous.

This is the most serious category, and everyone faces a greater risk of health effects.

Symptoms like chest pain, severe shortness of breath, confusion or difficulty speaking because of breathlessness require immediate medical attention.

“Very unhealthy or hazardous air should be taken seriously, regardless of whether you normally have breathing problems,” Dr. Gandhi says. “Your lungs are being exposed to a level of pollution that can cause symptoms in a much wider portion of the population.”

What to do: Stay indoors as much as possible and keep windows and doors closed.

Small adjustments can reduce how much pollution you breathe

A poor air quality day doesn’t always mean you have to remain indoors all day.

The AQI can change by the hour, and pollution can be lower at a different time. Shortening a strenuous outdoor activity or moving it indoors can reduce how much polluted air reaches your lungs.

People with asthma or COPD should continue following the treatment or action plan provided by their healthcare team. If you use a rescue inhaler, keep it nearby on days when air quality is poor in case symptoms begin or worsen.

“You don’t need to panic every time the AQI changes colors,” Dr. Gandhi says. “The goal is to understand what the level means, consider your personal risk and pay attention to how you feel.”