How Air Pollution Affects Your Health, EPA Data & Guidance

AQI Levels and What They Mean for Your Body

The Air Quality Index converts pollutant concentrations into a 0–500 scale with six color-coded categories. Each category represents a different level of health concern:

AQI Range	Category	Health Effect
0–50	Good	No health concern for most people.
51–100	Moderate	Unusually sensitive people may experience respiratory symptoms.
101–150	Unhealthy for Sensitive Groups	Children, elderly, and those with asthma/heart disease may be affected.
151–200	Unhealthy	Everyone may experience health effects; sensitive groups seriously affected.
201–300	Very Unhealthy	Health alerts for everyone; serious effects for sensitive groups.
301–500	Hazardous	Emergency conditions. Everyone is affected. Avoid all outdoor exertion.

Read the full breakdown in our Understanding the AQI guide. To check your area's typical AQI distribution, visit your state page or metro page.

Health Effects by Pollutant

Different pollutants affect the body differently. Understanding which pollutant is driving the AQI in your area helps you take targeted protective action:

Pollutant	Main Source	Short-Term Effects	Long-Term Effects
PM2.5	Vehicle exhaust, wildfire smoke, industrial emissions	Coughing, reduced lung function, aggravated asthma	Heart disease, lung cancer, premature death, cognitive decline
Ozone (O₃)	Forms from NOx + VOCs in sunlight	Chest tightness, throat irritation, reduced lung capacity	Permanent lung damage, increased asthma severity, premature death
PM10	Dust, construction, agriculture, pollen	Coughing, aggravated asthma, eye irritation	Respiratory disease with prolonged exposure
NO₂	Vehicle exhaust, power plants	Airway inflammation, increased asthma susceptibility	Linked to childhood asthma development
CO	Incomplete combustion (vehicles, fires)	Headache, dizziness, reduced oxygen delivery to organs	Heart stress with chronic low-level exposure

Learn more about each pollutant in our Common Air Pollutants guide.

Who Is Most at Risk?

Air pollution affects everyone, but certain groups experience health effects at lower pollutant levels than the general population:

Children (especially under 18): Lungs are still developing and respiratory rate is higher relative to body weight, so children inhale more pollutants per pound of body weight. Air pollution exposure during childhood is linked to reduced lung function that persists into adulthood.
Older adults (65+): Reduced cardiac and pulmonary reserve means the body is less able to compensate for air pollution stress. Older adults are at higher risk for pollution-triggered heart attacks and strokes.
People with asthma or COPD: Air pollution is the leading trigger of asthma attacks. Even moderate AQI levels can trigger symptoms in people with poorly controlled asthma. COPD patients face accelerated disease progression with chronic pollution exposure.
People with heart disease or diabetes: PM2.5 enters the bloodstream and causes systemic inflammation that can trigger cardiac events. Heart attack and stroke hospitalizations rise measurably during high-pollution episodes. Diabetics have heightened cardiovascular sensitivity.
Pregnant women: Research links PM2.5 exposure during pregnancy to preterm birth, low birth weight, and developmental effects. The fetus is especially sensitive during the first and second trimesters.
Outdoor workers: Farmworkers, construction workers, and delivery workers have prolonged outdoor exposure that exceeds what the AQI advisories are designed for. Even moderate AQI levels represent real risk with 8+ hours of outdoor physical exertion.

Short-Term vs. Long-Term Exposure

Air pollution harms health through two distinct pathways:

Short-term exposure (hours to days) at high AQI levels causes immediate symptoms: coughing, wheezing, shortness of breath, eye and throat irritation, chest tightness. For sensitive groups, even single high-pollution days can trigger asthma attacks, emergency room visits, and cardiac events. EPA air quality alerts are designed to address this acute risk.

Long-term exposure (years to decades) to even moderate pollution levels causes cumulative damage. The Global Burden of Disease Study estimates outdoor air pollution causes approximately 4.2 million premature deaths annually worldwide. In the US, EPA research links PM2.5 to reduced life expectancy, increased heart disease risk, and higher lung cancer rates even in areas that rarely exceed "Unhealthy" AQI thresholds.

This is why annual average air quality, not just peak days, matters for health. Check your area's median AQI and multi-year trends on the county and metro pages to understand your typical exposure level.

Practical Steps to Reduce Your Exposure

These evidence-based actions reduce air pollution exposure effectively:

On High-AQI Days

Check AQI before outdoor activity at AirNow.gov
Limit strenuous outdoor exercise when AQI exceeds 100 (sensitive groups) or 150 (general public)
Keep windows closed and use air conditioning on recirculate mode
Run a HEPA air purifier in bedrooms and main living areas
Wear a properly fitted N95 or KN95 respirator when outdoor exposure is unavoidable
Avoid exercising near busy roads even when regional AQI is moderate (near-road PM2.5 can be 2-3x higher)

For Long-Term Reduction

Use an air purifier with a true HEPA filter in your home, this is the single most impactful indoor intervention
Avoid idling vehicles near schools, parks, or windows
Choose housing and schools away from high-traffic roads and industrial facilities when possible
Replace gas stoves with electric or induction (gas combustion produces NO₂ and PM2.5 indoors)
Don't burn wood or trash, residential wood burning is a major PM2.5 source in many communities
Sign up for air quality alerts from your local air quality management district

Check Your Area's Air Quality Profile

PlainAir provides 5-year EPA AQS data for 977 counties, 496 metro areas, and all 53 states and territories. Understanding your area's typical air quality profile, not just today's AQI, helps you make better decisions about where to exercise, when to open windows, and what protective measures are most valuable for your situation.

Frequently Asked Questions

What is the most dangerous air pollutant for health?

PM2.5 (fine particulate matter with diameter of 2.5 micrometers or less) is considered the most dangerous common air pollutant. Its tiny size allows it to penetrate deep into the lungs and enter the bloodstream, causing systemic inflammation. Long-term exposure to PM2.5 is linked to heart disease, lung cancer, and premature death. Ground-level ozone is a close second, particularly for respiratory harm.

Who is most at risk from air pollution?

The groups most vulnerable to air pollution health effects are: children (developing lungs are more susceptible), older adults (65+, reduced physiological reserves), people with asthma or COPD, people with heart disease or diabetes, pregnant women (air pollution linked to low birth weight and preterm birth), and outdoor workers with prolonged exposure. These groups are advised to limit strenuous outdoor activity when AQI exceeds 100.

Can air pollution affect you even on "Good" AQI days?

For most healthy adults, Good AQI days (0-50) pose minimal risk. However, unusually sensitive individuals may experience effects even at these levels. Research also shows that long-term cumulative exposure, even to "moderate" levels (AQI 51-100), is associated with adverse health effects over years and decades. The AQI is calibrated for daily health decisions, not lifetime exposure risk.

Does wearing an N95 mask help with air pollution?

Yes, N95 and KN95 respirators filter at least 95% of airborne particles including PM2.5. Surgical masks and cloth masks provide much less protection against fine particles. During wildfire smoke events or high PM2.5 days, properly fitted N95s are the most effective wearable protection. They are less effective against ozone since ozone is a gas, not a particle.

How does indoor air quality compare to outdoor?

Indoors is generally better than outdoors during pollution events, but not always. Without ventilation or air filtration, indoor PM2.5 can reach 70-80% of outdoor levels within hours. Air purifiers with HEPA filters are highly effective at removing PM2.5 indoors. Ozone penetration is lower because ozone reacts with indoor surfaces. During normal conditions (not smoke events), indoor air quality is usually better than outdoor for most people.

Does air pollution cause cancer?

The International Agency for Research on Cancer (IARC) classified outdoor air pollution as a Group 1 carcinogen in 2013, meaning there is sufficient evidence it causes cancer in humans. PM2.5 specifically is a Group 1 carcinogen. Long-term exposure is linked primarily to lung cancer, but also to bladder cancer. Living near heavy traffic is associated with increased lung cancer risk independent of smoking.

Sources

U.S. Environmental Protection Agency — Health Effects of Air Pollution
U.S. Environmental Protection Agency — Air Quality System (AQS), 2020–2024
EPA — Integrated Science Assessment for Particulate Matter (2019)
International Agency for Research on Cancer (IARC) — Monograph on Outdoor Air Pollution (2013)
Global Burden of Disease Study 2019 — Air Pollution Risk Factors

This content is for informational purposes only and does not constitute medical advice. Consult a healthcare provider for personal health guidance. For current air quality conditions, visit AirNow.gov.