Air Pollution: How It Enters Our Bodies

Air pollution is a major threat to global health, with 99% of people breathing air that exceeds the World Health Organization's (WHO) guideline limits for pollutants. It is caused by the release of hazardous substances from both human-made and natural sources, such as vehicle emissions, fuel oils, natural gases, manufacturing by-products, and wildfires. These pollutants enter the body primarily through the respiratory tract, leading to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells. Due to their small size, some pollutants can penetrate the bloodstream via the lungs, circulating throughout the body and causing systemic issues. The effects of air pollution vary depending on factors such as age, location, and individual health, but it is linked to various diseases, including stroke, heart disease, lung cancer, and respiratory problems.

Fine particles enter the lungs and bloodstream

Air pollution is a mix of hazardous substances from both human-made and natural sources. It is a major threat to global health, killing 7 million people every year. The primary sources of human-made air pollution are vehicle emissions, fuel oils, natural gases, manufacturing by-products, and power generation.

Fine particles, also known as particulate matter (PM), are one of the most concerning air pollutants for human health. PM is a mix of tiny solid and liquid particles suspended in the air we breathe. These particles are so small that they are invisible to the naked eye, and they can only be seen with an electron microscope. The inhalation of these fine particles can lead to serious health problems.

Due to their small size, fine particles can penetrate deep into the lungs and even enter the bloodstream. This occurs through four different mechanisms: interception, impaction, sedimentation, and diffusion. Interception happens when a particle travels so close to a surface of the airway that it touches and deposits onto the surface. Impaction occurs when particles suspended in the air encounter a bend in the airway and stick to a surface in their original path. Sedimentation is when the air slows down enough for particles to "settle" out, usually in the alveolar region of the lower lung area. Finally, diffusion refers to the random motion of particles similar to gas molecules, which allows them to deposit on lung walls.

Once in the lungs and bloodstream, fine particles can cause systemic inflammation and damage to tissues and cells throughout the body. This can lead to an increased risk of various diseases, including stroke, heart disease, respiratory disease, lung cancer, and dementia. There is no safe threshold for breathing in fine particles, and even short-term exposure can have negative health impacts.

Pollutants cause inflammation and cell damage

Air pollution is a mix of hazardous substances from both human-made and natural sources. The primary sources of human-made air pollution are vehicle emissions, fuel oils, natural gas, by-products of manufacturing and power generation, and fumes from chemical production. Natural sources include smoke from wildfires, ash and gases from volcanic eruptions, and gases from decomposing organic matter in soils.

The main pathway of exposure to air pollution is through the respiratory tract. Some pollutants are so fine that they can be inhaled deeply into the lung tissue and enter the bloodstream, travelling to and damaging other organs in the body. These fine particles can cause systemic inflammation and carcinogenicity, impacting the lungs, heart, and brain, among other organs, and ultimately leading to disease.

The World Health Organization (WHO) has found links between exposure to air pollution and type 2 diabetes, obesity, systemic inflammation, Alzheimer's disease, and dementia. A large study also associated high levels of air pollutants with bone damage, particularly in the lumbar spine, among postmenopausal women. In children, exposure to air pollution has been linked to asthma, slower processing speed, attention-deficit and hyperactivity disorder (ADHD) symptoms, and other neurobehavioural problems.

In addition to the health risks, air pollution also has economic implications, with the healthcare sector bearing significant costs associated with treating diseases related to exposure to air pollution.

Air pollution impacts almost every organ

Air pollution is a mix of hazardous substances from both human-made and natural sources. It is a familiar environmental health hazard, with nine out of ten people now breathing polluted air, which kills 7 million people every year. The primary sources of human-made air pollution are vehicle emissions, fuel oils, natural gas, by-products of manufacturing and power generation, and fumes from chemical production. Natural sources include smoke from wildfires, ash and gases from volcanic eruptions, and gases like methane emitted from decomposing organic matter in soils.

The main pathway of exposure from air pollution is through the respiratory tract. Breathing in these pollutants leads to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body, impacting almost every organ. Due to their small size, some air pollutants can penetrate into the bloodstream via the lungs and circulate throughout the entire body, leading to systemic inflammation and carcinogenicity. This can cause damage to the brain, kidneys, and pancreas, and increase the risk of dementia, strokes, and reduced intelligence.

The lungs are also directly affected by air pollution, with short-term exposure to higher levels of outdoor air pollution associated with reduced lung function, asthma, and cardiac problems. Air pollution is a risk factor for all-cause mortality and specific diseases, including stroke, ischaemic heart disease, chronic obstructive pulmonary disease, lung cancer, and pneumonia.

In addition to the respiratory and cardiovascular systems, air pollution has been linked to adverse pregnancy outcomes, such as low birth weight and small for gestational age, other cancers, diabetes, cognitive impairment, and neurological diseases. There is also evidence of damage to reproductive health, with studies showing increased miscarriages and reduced fertility associated with air pollution exposure.

The liver, skin, bones, and even the unborn are not exempt from the detrimental effects of air pollution. Research has found pollutants in placentas nourishing foetuses, while skin ageing, hives, and brittle bones have also been linked to toxic air.

Outdoor and indoor air pollution are both dangerous

Outdoor air pollutants can enter buildings through open doors and windows, ventilation systems, and cracks in structures. For example, harmful smoke from chimneys can re-enter homes and pollute the indoor air. Some pollutants enter through building foundations, such as radon, which forms in the ground as uranium in rocks and soils decays. In areas with contaminated water or soils, volatile chemicals can enter buildings in the same way. These chemicals can also enter indoor air when building occupants use the water, for example, during showering or cooking. People can also bring in outdoor pollutants on their shoes and clothing.

Indoor air pollution is generated by the use of inefficient and polluting fuels and technologies, which contain a range of health-damaging pollutants, including small particles that penetrate deep into the lungs and enter the bloodstream. In poorly ventilated dwellings, indoor smoke can have levels of fine particles 100 times higher than acceptable. Exposure is particularly high among women and children, who spend the most time near the domestic hearth and are often responsible for household chores such as cooking and collecting firewood.

Indoor air pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions and by not carrying indoor air pollutants out of the area. High temperatures and humidity levels can also increase concentrations of some pollutants. Many factors contribute to poor indoor air quality, including human activities within buildings, such as smoking, burning solid fuels, cooking, and cleaning. Vapors from building and construction materials, equipment, and furniture, as well as biological contaminants such as mold, viruses, and allergens, can also affect indoor air quality.

Air pollution is a global health crisis

Air pollution is a pressing global health crisis that demands urgent interdisciplinary action. It is a familiar environmental health hazard, with brown haze settling over cities, exhaust billowing across highways, and plumes rising from smokestacks. According to the World Health Organization (WHO), almost the entire global population (99%) breathes air that exceeds the recommended limits and contains high levels of pollutants. This includes outdoor air pollution in both cities and rural areas, as well as indoor air pollution from household activities. The main pathway of exposure to these pollutants is through the respiratory tract, where they cause inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body.

The health impacts of air pollution depend on the types, sources, and concentrations of the pollutants. However, the specific disease outcomes most strongly linked to air pollution exposure include stroke, ischaemic heart disease, chronic obstructive pulmonary disease, lung cancer, pneumonia, and cataract (household air pollution only). There is also suggestive evidence linking air pollution exposure to an increased risk of adverse pregnancy outcomes, other cancers, diabetes, cognitive impairment, and neurological diseases. Fine particulate matter, or PM2.5, is of particular concern as it can penetrate deep into the lungs, enter the bloodstream, and travel to organs, causing systemic damage to tissues and cells. Other pollutants of major public health concern include carbon monoxide, ozone, nitrogen dioxide, and sulfur dioxide.

Vehicle emissions, fuel oils, natural gas used for heating, by-products of manufacturing and power generation, and fumes from chemical production are the primary sources of human-made air pollution. Nature also contributes to air pollution through smoke from wildfires, ash and gases from volcanic eruptions, and gases like methane emitted from decomposing organic matter. As the world gets hotter and more crowded, our engines continue to pump out dirty emissions, and half the world lacks access to clean fuels and technologies. This has resulted in dangerously polluted air, with nine out of ten people now breathing polluted air, leading to approximately 7 million deaths annually.

To address this global health crisis, the WHO and partners convened the first Global Conference on Air Pollution and Health in 2018 to raise awareness and share information on the health risks of air pollution and potential interventions. The WHO has also developed a strategy to raise awareness about the risks of air pollution and provide solutions to mitigate exposure risks. Additionally, the United States Environmental Protection Agency (EPA) has implemented regulatory programs under the Clean Air Act to reduce air pollution and protect human health and the environment. Despite these efforts, air pollution continues to harm people's health worldwide, underscoring the urgency of interdisciplinary action to tackle this crisis.

Frequently asked questions