Air pollution affects virtually everyone on the planet. More than 99% of the global population breathes air that exceeds the World Health Organization’s safety guidelines, and 6.7 million people die prematurely from polluted air each year. But the burden is not shared equally. Certain groups face far greater risks because of their biology, where they live, what they do for work, or health conditions they already have.
Children and Developing Lungs
Children are among the most vulnerable. Around 93% of children under 15 breathe polluted air daily, and even low levels of pollution harm their lung function, slow lung growth, and increase rates of asthma, bronchitis, and respiratory infections. The reasons are straightforward: children breathe faster than adults relative to their body size, taking in more polluted air per kilogram. Their lungs are also still forming. Alveoli, the tiny air sacs where oxygen enters the blood, continue developing well into adolescence. Damage during this window doesn’t just cause childhood illness. A study tracking nearly 1,400 people from childhood into adulthood found that reduced lung function early in life is a risk factor for chronic obstructive pulmonary disease (COPD) later on.
Children’s bodies are also less equipped to handle the damage pollution causes at a cellular level. Their detoxification systems are less efficient than adults’, meaning the oxidative stress and inflammation triggered by pollutants hit harder and linger longer. The harm can begin before birth: exposure to fine particulate matter during pregnancy is associated with lower birth weight and a higher chance of preterm delivery. A Spanish study of 3.6 million births found that for every 10 microgram increase in coarse particulate matter during pregnancy, birth weight dropped by about 7 grams on average and the odds of preterm birth rose by 4%. The third trimester appeared to be the most sensitive window.
Older Adults and Heart Disease Risk
Adults over 65 face a different set of dangers, concentrated heavily in the cardiovascular system. Large studies across multiple countries have linked particulate matter exposure in older adults to increased hospital admissions for heart attacks, congestive heart failure, and both types of stroke. A Chinese study of nearly 461,000 people aged 65 and older found that short-term spikes in fine particulate matter (PM2.5) increased admissions for coronary heart disease. A Belgian study of adults 75 and older reported that the heart attack risk associated with PM2.5 was greater in elderly patients than in younger ones.
The pattern holds across geographies. Research in Korea following over 900,000 older adults linked PM2.5 to higher cardiovascular mortality overall, while Japanese data showed increased stroke risk on high-pollution days. These aren’t subtle statistical effects. For older adults whose hearts and blood vessels are already strained by age, a bad air quality day can be the trigger for a serious cardiac event.
People With Asthma and COPD
If you already have a chronic lung condition, air pollution doesn’t just add discomfort. It sends people to the hospital. A Berlin study found that for every 10 microgram increase in nitrogen dioxide (NO2), the risk of same-day hospitalization rose about 10% for asthma patients and 12% for those with COPD. These increases occurred at pollution levels well below European regulatory limits, meaning there’s no “safe” threshold for people with compromised airways.
NO2, which comes primarily from vehicle exhaust and power plants, was the pollutant most consistently tied to flare-ups in this research. The mechanism is well understood: pollutants trigger inflammation in airways that are already chronically inflamed, narrowing them further and making it harder to breathe. For the hundreds of millions of people worldwide living with asthma or COPD, air quality forecasts aren’t abstract numbers. They’re information that determines whether it’s safe to go outside.
Pregnant Women and Fetal Development
Pregnancy creates vulnerability for both the mother and the developing baby. Fine particulate matter can cross the placenta, and exposure during pregnancy is consistently linked to lower birth weight and higher rates of preterm birth. The Spanish birth registry study, one of the largest ever conducted on this question, found these effects were strongest during the third trimester, when the fetus is gaining the most weight. Importantly, the associations strengthened at PM2.5 levels above 10 micrograms per cubic meter, a threshold that the vast majority of the world’s population exceeds.
The risks also compound with disadvantage. Babies born to mothers with lower education levels, particularly those living in economically deprived areas, showed stronger associations between pollution exposure and poor birth outcomes. This likely reflects both higher exposure and fewer resources to mitigate it.
The Brain: Cognitive Decline and Dementia
One of the more alarming findings in recent years is the link between long-term air pollution exposure and dementia. A meta-analysis published in The Lancet Planetary Health, pooling data from 21 studies covering over 24 million people, found that every 5 microgram increase in long-term PM2.5 exposure was associated with an 8% higher risk of developing dementia. This makes air pollution a modifiable risk factor for cognitive decline, relevant to anyone aging in a polluted environment but particularly concerning for people already at elevated risk due to genetics or other health conditions.
Workers Exposed on the Job
Certain occupations put people in polluted air for hours every day, often without the option to stay indoors. An American Thoracic Society report identified agricultural workers, construction workers, and wildland firefighters as the highest-risk groups.
- Agricultural workers face exposure from dust, pesticide drift, and equipment exhaust. They were flagged as particularly vulnerable because legal and social marginalization often limits their access to protections and healthcare.
- Construction and road workers make up about 6% of the U.S. workforce but account for 36% of heat stroke deaths, reflecting how much time they spend outdoors in harsh conditions. They also breathe volatile organic compounds, traffic-related pollution, silica dust, and nitrogen dioxide as part of their daily work.
- Wildland firefighters routinely inhale smoke at concentrations that would trigger emergency warnings for the general public. Research has found they face an estimated 16 to 30% increased risk of cardiovascular disease compared to the general population, along with higher rates of asthma, COPD, and pneumonia linked to hours spent on active fire lines.
Warehouse workers and others in indoor spaces near pollution sources are also at risk, since outdoor pollutants infiltrate buildings with poor ventilation.
Low-Income and Minority Communities
Where you live often determines how much pollution you breathe, and that’s shaped heavily by income and race. Across North America, research consistently shows that lower-income communities and communities of color are exposed to higher concentrations of harmful air pollutants. This isn’t coincidental. Factories, highways, and other pollution sources are disproportionately sited in neighborhoods with less political power to resist them. Decades of race-based and class-based residential segregation have concentrated these exposures in predictable ways.
The pattern is clearest in the United States and Canada, where the evidence is extensive. European research has been more mixed, with some countries showing similar disparities and others less clear trends. Globally, the WHO notes that air pollution reduction would be especially beneficial for children in low- and middle-income countries, where nearly 9 out of 10 urban residents are affected. The inequality runs in both directions: these communities face more pollution and have fewer resources (healthcare, air filtration, ability to relocate) to manage its effects.
How Much Pollution Is Too Much
The WHO updated its air quality guidelines in 2021, lowering the recommended annual PM2.5 limit from 10 to 5 micrograms per cubic meter after mounting evidence that health damage occurs even at very low concentrations. Under current conditions, more than 90% of the world’s population is exposed to levels above this new guideline. Even by the older, more lenient standard, over 75% of people breathe air that’s too dirty.
This means air pollution isn’t a problem limited to visibly smoggy cities or industrial zones. It affects people in suburbs, small towns, and rural areas near agricultural operations or wildfire zones. The groups described above bear the heaviest burden, but the scale of exposure means almost no one is untouched.