TL;DR— This blog takes a deep dive into the vast array of impacts that air pollution has on human health, exploring how poor air quality affects nearly every area of the human body — from head to toe. Research shows that air pollution is a major environmental risk factor for a slew of diseases, from Alzheimer’s disease to lung cancer to osteoporosis, and can significantly lower lifespan and quality of life. Air pollution accounts for extensive damages to public health, as well as vast economic losses due to healthcare costs and lost school and workdays. While air pollution exposure can impact everyone, its damage is not distributed equally. Children, elderly individuals, those with pre-existing conditions, and those living in low socioeconomic neighborhoods or environmental justice communities bear a disproportionate burden of its impacts — emphasizing the need to protect vulnerable populations by taking better care of our air quality.

The overall health and economic impacts of air pollution

We know that air pollution is responsible for approximately 7 million premature deaths per year, but what do the impacts of air pollution look like at the level of individual human health?

Air pollution is the major environmental driver associated with a multitude of diseases, including respiratory conditions such as asthma and lung cancer; neurological diseases like Alzheimer’s and Parkinson’s disease; a variety of psychological conditions; and a slew of other outcomes, including disrupted fetal growth, autism, retinopathy, and low birth weight.

With this myriad of air pollution-associated health outcomes, many studies have looked to quantify the impacts that air pollution has on the general population — one methodology employed by the USEPA is provided as an example below. 

Research by the USEPA finds that certain health conditions, such as the respiratory effects of air pollution exposure, can be directly linked to their economic consequences, such as the costs associated with doctor visits, lost school and work days, hospital visits, and, ultimately, deaths. Such research helps to provide a rubric by which we can evaluate the vast amounts of human health damage that come from air pollution, in terms of the exact costs suffered by society and the economy at large. (Image source: USEPA)

Projections looking at how these costs are projected to change over time appear grim. Research from the OECD’s Economic Consequences of Air Pollution project finds that by 2060, global economic output will be reduced by approximately $330 USD per person, coupled with $155 billion increases in annual healthcare costs and 2.5 billion more lost workdays at the global level. 

On a global economic level, the project estimates that these economic impacts of air pollution — including decreased labor productivity, increased healthcare costs, and lost agricultural crop yields — will cost 1% of global GDP by 2060.

The Organisation for Economic Co-operation and Development (OECD) conducted research looking at how the health, economic, and productivity-related outcomes of air pollution exposure may change from 2010 to 2060. Vast increases in respiratory outcomes, healthcare costs, lost workdays, and restricted activity days suggest that air pollution will have a monumental impact on global health and wellbeing if steps are not taken to improve air quality. (Image source: OECD)

A breakdown of the health impacts of air pollution, from head to toe

While intuitively we understand that air pollution damages the lungs, research is continually uncovering how it truly impacts nearly every organ in the human body. Air pollution particles can be small enough to enter the bloodstream, and from there they cause systemic inflammation and wreak havoc on our natural bodily functions. The infographic below provides an overview of how different parts of the body are impacted by air pollution. 

In general, the wide-reaching damage caused by air pollution is thought to be a result of the systemic inflammation it causes. Given the importance of having our entire body working properly for optimal human health, we thought we would take a look at how each of these body parts is negatively impacted by air pollution.

Eye health

Air pollution is linked to a variety of eye issues, including asymptomatic eye problems and dry eye syndrome. Research on this connection suggests that air pollution can irritate the eyes through irradiation of automobile exhaust.

The eyes are a sensitive organ with a particularly high level of blood flow, making them more sensitive to damage caused by air pollution, especially the small components of fine particulate matter that can circulate the body after being inhaled. 

A large UK-based study found that even small increases in air pollution are associated with age-related macular degeneration, which causes irreversible sight loss. Even increases in particulate matter on the order of 1 μg/m3 were linked to an 8% increase in the risk for age-related macular degeneration (AMD).

Neurological effects of air pollution exposure

Though historically air pollution’s link to respiratory health has been well-studied, increasing amounts of research regarding the connection between poor air quality and neurological and cognitive health outcomes have been released in recent years. Research suggests that cognitive decline, dementia, anxiety, depression, ADHD, and schizophrenia all occur at greater frequency with exposure to various air pollutants. 

Specific pollutants, such as lead, have also been studied for their connection to learning disabilities, memory impairment, hyperactivity, and antisocial behaviors in children. Children’s brain development can also be impacted by exposure to high levels of ambient air pollution while they are in the womb because the brain is still developing at this time and air pollution can cause permanent brain damage. Even in utero, high air pollution exposure can also lead to cognitive impairment in old age.

A study examining nitrogen dioxide finds that this pollutant is one of the main causes of stroke.  The same study found short-term exposure to sulfur dioxide and PM10 was also associated with an increased risk of stroke.

A study out of USC has examined the link between air pollution and dementia — this study of over 2,000 older women over 10 years suggests that not only does air pollution exposure contribute to a higher risk of dementia, but improved air quality can also slow this accelerated aging of the brain. 

…lowering air pollution exposure to roughly 15 percent below the EPA’s current standard threshold led to a 20 percent reduction in dementia risk.”

— Jiu-Chiuan Chen, researcher at USC

Other recent research presented at the 2021 Alzheimer’s Association International Conference found similar outcomes. Reducing PM2.5 and NO2 pollution by 10% of the USEPA’s current standard over 10 years was linked to 14% and 26% reductions in dementia risk in older women in the United States — including when the results were controlled for age, education, region, and presence of cardiovascular disease.

While the exact mechanisms behind this link between air pollution and dementia are not yet fully understood, recent research looking at beta-amyloid levels in the blood suggests a potential biological link between air pollution and Alzheimer’s-related changes to the brain.

A video from Harvard University elucidates how the inflammation caused by fine particulate matter can lead to detrimental neurological and cognitive effects.

Respiratory health

The link between air pollution and respiratory health is perhaps the best understood. Many negative health impacts can be seen in the respiratory system because it acts as the first line of defense against air pollutants inhaled into the body. 

Particle pollution is linked to a long list of respiratory outcomes, such as:

  • Cough, phlegm, wheezing
  • Development of asthma
  • Airway and lung inflammation
  • Respiratory infection
  • Decreased lung function and growth in children
  • Emergency room and hospital visits due to respiratory symptoms
  • Premature death

The size of the particles which make up particulate matter affects how detrimental pollution exposure is to respiratory health. Particulate matter is generally divided into PM10 and PM2.5 —  the latter of which contains finer particles that can enter deeper into the lungs and body. Smaller particles can reach the lower respiratory tract and thus can cause lung and heart disease with a greater likelihood.

In addition to illness caused by PM exposure — characterized by symptoms such as coughing, dry mouth, and wheezing — research also demonstrates that particulate matter can cause premature death in those with existing heart or lung conditions.

Cardiovascular health

Research demonstrates a clear link between air pollution exposure and worsened cardiovascular health. A variety of studies have found the following relationships:

  • For every 5~6 μg/m3 increase in fine particulate matter, a 0.5% to 1.5% increase in the prevalence of cardiovascular disease
  • After acute exposure to particulate matter air pollution, a 69% increase in deaths due to cardiovascular causes
  • For every 10.5 μg/m3 increase in PM2.5, the risks of ischemic heart disease, heart failure, arrhythmias, and cardiac arrest increased by 8% to 18%
  • A study looking at 43 million people across 29 major European cities found that for every 10 μg/m3 increase in PM10, there was an associated 0.76% increase in the risk of cardiovascular death; notably, this was a higher associated increase than was observed for respiratory diseases

A 2016 study also noted that exposure to both particulate matter and nitrogen dioxide at levels close to those stated by the National Ambient Air Quality Standards (NAAQS) were linked to prematurely aged blood vessels, causing calcium buildup in the coronary artery, suggesting that this may be the mechanism through which air pollution so severely damages cardiovascular health.

Impacts on the digestion system

Studies have found an association between air pollution exposure and a slew of gastrointestinal diseases, such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), appendicitis, and intestinal infections in infants. 

Animal studies that aim to examine the link between air pollution and harm to the digestive system find that inhaled particulate matter pollution can alter the microbiome composition within the body. A 2020 study that establishes this link in humans finds that ozone pollution may play an important role in this process.

Air pollution’s effects on the liver

Long-term exposure to high levels of air pollution has been linked to metabolic-associated fatty liver disease (MAFLD) in animal studies, suggesting detrimental impacts on humans. This disease affects a quarter of the global population and has increased in incidence steadily since the 1980s. MAFLD can progress to liver diseases such as liver cancer and cirrhosis, presenting a serious threat to human health.

The link to diabetes

Research estimates that in 2016, air pollution contributed to 3.2 million new cases of diabetes across the world and that 8.2 million years of healthy life were lost due to pollution-linked diabetes. The same study attributes 150,000 new cases of diabetes — and an associated loss of 350,000 years of healthy life — to air pollution each year in the United States alone.

Further research is still needed to understand a possible mechanism that explains this link between air pollution and diabetes. Scientists have suggested that inhaled air pollutants that enter the bloodstream can disrupt the body’s organs and may affect insulin sensitivity and production. 

A figure from the 2016 study by Bowe et al. from The Lancet shows the relative risk of developing diabetes (along the y-axis) compared to the concentration of PM2.5 pollution (along the x-axis), while the gray histogram in the background shows the distribution of PM2.5 pollution among the 194 countries studied. The red line shows an increasing relative risk as the PM2.5 concentration increases. The study finds that ambient particle pollution contributed to 3.2 million cases of diabetes globally and over 206,000 deaths attributable to diabetes from PM2.5 exposure. (Image source: Bowe et al.)

We do know that in lower-income countries that lack clean air policies, citizens have a greater risk of pollution-related diabetes. However, studies show that the risk of pollution-related diabetes increases dramatically even at very low pollution exposure levels, so this risk remains even in places where air quality is deemed acceptable — showing that there is truly no safe level of air pollution.

Reproductive health and fertility

Many studies demonstrate that air pollution exposure has a clear effect on reproductive health and fertility. One Chinese study of over 18,000 couples found a connection between moderate levels of fine particulate matter pollution and a 20% greater risk of infertility, defined as not becoming pregnant within a year of trying. 

A Harvard study looked specifically at women undergoing in vitro fertilization and found that those that lived closer to major roads were less likely to have successful embryo implantation and live birth as compared to those living further away. 

Air pollution due to wildfire smoke — which tends to be severe but short-lived — also has a significant effect. A study out of Stanford University found that over the course of 2007 to 2012, an additional 7,000 preterm births resulted from the effects of wildfire smoke. The researchers also found that the amount of time the mother was exposed to wildfire smoke was directly related to how likely she was to have a preterm birth. With wildfire seasons in the United States worsening in intensity and frequency since 2012, this number of preterm births is likely higher now.

We found that a week’s worth of smoke exposure [at moderate to severe levels] was associated with a 5% increased risk and a month’s worth was associated with a 20% increase in preterm births”

— Sam Heft-Neal, lead author of Stanford study looking at wildfire smoke’s impacts on pregnancy and preterm birth

Human male reproductive health is also impacted by air pollution — studies find that poor air quality can affect semen quality and could cause sperm DNA damage, thus harming fertility. This relationship is likely related to the concentration and duration of exposure to air pollutants.

While like many health impacts of air pollution, the mechanism behind this relationship is not yet fully understood, research demonstrates the extent of air pollution’s impact on both overall and reproductive health. Animal and human studies suggest that air pollution may create damage during the reproductive process of gametogenesis, therefore decreasing reproductive capacities.

Exposure to high levels of air pollution in the womb can also lead to premature birth, low birth weight, and infant mortality.

Bone and musculoskeletal health

Though not extensively studied, research finds that ambient air pollution exposure is associated with lower levels of bone mass, perhaps due to particle inhalation causing oxidative stress and inflammation in the body that ultimately affects bone health. This relationship holds true across a wide range of air pollution levels associated with low-, middle-, and high-income areas.

Studies that specifically examined osteoporosis and bone fractures resulting from air pollution found that populations exposed to higher levels of fine particulate matter had lower bone mineral density as well as higher hospitalization rates for bone fractures. Because certain regions of the world, such as Asia, already tend to have a higher risk for osteoporosis, the effects of poor air quality only compound this danger.

Health impacts of air pollution as a whole

After taking a deep dive into the way that air pollution affects a variety of different systems, organs, and parts of the body, we can answer the question: What do these health impacts add up to?

Lowered life expectancy is a well-studied result of air pollution exposure. Research from the University of Chicago suggests that if particulate matter air pollution is not lowered to the World Health Organization’s recommended level, the average person could lose 2.2 years of life. The number is even higher for those living in more polluted regions, who could lose 5 years or more.

Significant decreases in quality of life also result from exposure to air pollution. For example, reduced lung function in children and adults that leads to asthmatic bronchitis and chronic obstructive pulmonary disease (COPD) can greatly lower one’s quality of life, as can dementia, cardiovascular disease, and many of the other health outcomes discussed above.

Air pollution exposure is also linked to increased cancer risk. Apart from the types of cancer found in the lungs, air pollution’s damage to the body as a whole means an increased risk of other cancers as well. 

One study analyzed 5 years of USEPA data to identify over 1,000 toxic hotspots of air pollution across the United States, where 250,000 people living in these areas were exposed to levels of cancer risk above what the USEPA deems acceptable. Even in those areas under the 1 in 10,000 risk rate that the EPA allows, researchers still say that the risk is high enough to be of concern.

Criteria air pollutants and their health impacts

For more specific information breaking down key air pollutants and their health effects, read our Air Quality Measurements Series blogs, where we detail particulate matter, nitrogen dioxide, and ground-level ozone pollution, as well as the way wind speed and direction impact air pollution distribution. A summary table for the six criteria air pollutants regulated by the USEPA is provided below. 

Criteria air pollutants — a classification of six different harmful air pollutants by the USEPA, as listed above — are linked to their major sources of emission and the primary health impacts that they are responsible for. Damage can be seen across the body, from respiratory and cardiovascular impacts to those damaging the central nervous system. (Image source: Ghorani-Azam et al.)

The concentration of health impacts in vulnerable populations

Exposure to air pollution is not created equal. Certain populations tend to be more susceptible to the negative health effects of air pollution, such as elderly individuals and those with pre-existing heart and lung disease.

Children tend to be more sensitive to air pollution for a variety of reasons: their lungs and alveoli are still developing, they have narrower airways and breathe more air per pound of bodyweight than adults, and they tend to be more active outdoors for longer periods, causing them to breathe in more air pollution than adults typically do.

Those that live in low socioeconomic communities also tend to disproportionately experience the negative impacts of poor air quality — and higher exposure levels to criteria air pollutants — because these neighborhoods tend to be closer to industrial facilities and other sources of air pollution. A variety of other factors, including a history of class- and race-based residential segregation, contribute to this issue. For more information, read our blog about improving air quality in environmental justice communities.

Making sense of air pollution’s impact

Research has demonstrated the numerous negative health impacts posed by air pollution across the body, in general quality of life, and across different susceptible populations.

Many studies found that negative health impacts resulted even at air pollution levels well below the WHO guidelines — reminding us that there is truly no safe level of air pollution. Fortunately, in light of the abundance of research demonstrating the multifaceted health impacts of even relatively low levels of air pollution, the WHO recently updated their guidelines to recommend even stricter regulations on air pollution

Monitoring ambient air quality is the first step in protecting our air. By gathering data to understand air pollution exposure, action can be taken to reduce air pollution. Environmental policy improvements can be made on local, state, tribal, and federal levels to protect both our air quality and other facets of environmental health, such as our climate.

On a personal level, it’s helpful to understand the risks of air pollution in your area to have a sense of your exposure to air pollution. To find out more about the air quality in your area, you can explore the EPA’s Fire and Smoke Map in the United States and the OpenAQ global platform.