Air Pollution

Overview

Exposure to air pollution can have major impacts on overall health. Air pollution was initially regarded primarily as a threat to respiratory health. That concern now includes a broader range of health issues, including cardiovascular disease, stroke, cancers, cognitive function, adverse pregnancy outcomes, Parkinson’s disease, diabetes, depression, and increased risk of death. Although air pollution can’t be completely avoided, people can take steps to reduce their exposure to outdoor and indoor air pollution.

Key Types of Air Pollutants

• Traffic-Related Air Pollution (TRAP) includes a mix of gases and particles released into the air in the exhaust of cars, buses, and trucks. This includes ozone, particles, gases, and volatile organic compounds.
• Ozone, often called smog, forms when pollution from cars, factories, and power plants react with sunlight.
• Particulate Matter (PM) is the dust, soot, and chemicals in the air. Much of it comes from the burning of coal, gasoline, or forest fires. The particles range in size. Coarse particles (such as PM10), are the largest. Fine particles, known as PM2.5, are about 30 times thinner than human hair. Ultrafine particles are even smaller and are measured in nanometers. Fine and ultrafine particles are of more concern as they can go deep into lungs when inhaled and can cause health problems.
• Noxious gases are harmful substances like carbon dioxide, carbon monoxide, nitrogen oxides, and sulfur oxides released into the air by fossil fuels, car exhaust or by factories.
• Volatile Organic Compounds (VOCs) are vaporized compounds given off by gasoline and natural gas but also everyday items like paints, cleaning supplies, vinyl materials, pesticides, some furnishings, and glue.
• Polycyclic aromatic hydrocarbons (PAHs) are chemicals released by power plants or during the creation of products like iron, steel, and rubber. Of the more than 100 known polycyclic aromatic hydrocarbons in the environment, 15 are listed in the Report on Carcinogens.

Indoor Air Pollution

We tend to think of air pollution as a risk faced outside, but the air we breathe indoors can also be affected.

Indoor air pollutant sources include:

• Human activities such as smoking, burning solid fuels, cooking, and cleaning
• Vapors from building and construction materials, equipment, and furniture
• Biological contaminants such as pollen, mold or viruses
• Allergens including chemicals used as fragrance

Related Health Effects

Air pollution is linked to health problems in the respiratory, cardiovascular, reproductive, neurological, and immune systems.

Respiratory Disease

Air pollution can affect lung development and has been linked to reduced lung function, emphysema, asthma, bronchitis, chronic obstructive pulmonary disease (COPD) and other respiratory diseases in people of all ages. Symptoms of these conditions include coughing, wheezing, chest tightness, or shortness of breath. Many studies find these effects even after short-term contact with outdoor air pollution. Regular and long-term exposure can worsen symptoms and create lasting health effects.

Cardiovascular Disease

Long-term exposure to particles and traffic emissions have been associated with increased incidence of cardiovascular diseases. Breathing of fine (PM2.5) particles also can affect blood vessels, speed up hardening and narrowing of arteries, and even trigger heart attacks.

Exposure to gases like nitrogen oxides has been tied to higher risk of stroke. Short-term exposure to ozone has been linked to greater risk for blood clotting and high blood pressure

Cancer

The breathing of air pollution particles and gases has been linked to an increased risk of lung cancer. It also has been tied to higher levels of breast cancer, colon cancer, prostate cancer, as well as ovarian and uterine cancer.

Neurological Effects and Dementia

NIH-funded research has found strong links between air pollution, especially airborne particles and conditions like Parkinson’s disease, dementia (including Alzheimer’s disease), and depression.

Diabetes

Long-term exposure to pollution particles and gases has been associated with increased diabetes risk.

Women’s Health and Pregnancy Outcomes

Air pollution exposure has adverse effects on pregnant women and young infants. These can include high blood pressure, higher rates of infant death, preterm birth, low birth weight, and problems with infant lung development.

Children’s Health

Children are especially susceptible to health problems linked to air pollutants. Air pollution has been linked in multiple systematic reviews to autism risk. In addition, prenatal and childhood exposure to PM2.5 (fine particles) has been linked to brain development effects.

Causes and Risk Factors

Causes of Outdoor Air Pollution 

Vehicle emissions, natural gas to heat homes, by-products of manufacturing and power generation, particularly coal-fueled power plants, and fumes from chemical production are the primary sources of human-made air pollution. 

Causes of Indoor Air Pollution 

Indoor air pollutants include asbestos fibers, dust, formaldehyde from plywood and carpets, pesticides, volatile organic compounds, flame retardants, radon, and smoke. Gas stoves and heating units, if not properly vented, can contribute to pollutants like carbon monoxide and nitrogen dioxide. Many outdoor air pollutants also can penetrate the indoor environment and accumulate, especially if buildings have poor ventilation.

Weather and Environmental Risks

Warm temperatures trap ozone and particles in the air and promote pollen production, increasing the chance of allergies and respiratory diseases. In communities with high ozone levels and other air pollutants, children are more likely to develop asthma. Hot, dry temperatures contribute to wildfires and smoke-related ailments that can reduce lung function. Heavy rainfalls and storms can promote mold growth and release pollutants that trigger airway inflammation and spur cases of asthma.

Prevention Guidance

Individuals can reduce indoor air pollution at home by taking the following steps:

• Avoid smoking or using items like fireplaces, wood-burning stoves, and candles that produce smoke.
• Avoid using products with strong odors, such as bleach, cleaning products, air fresheners, and perfumes.
• Use high-efficiency particulate air (HEPA) filtration devices and proper safety equipment when using chemicals.
• Fix water leaks promptly to reduce mold.
• Vacuum and keep surfaces clean to reduce dust and allergens.
• Keep windows closed during high allergen days and use air conditioning when possible.
• Have heating and cooling systems inspected yearly.

People can monitor air quality in real time anywhere in the United States using AirNow.gov.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on air pollution.

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.  

NIH continues to support research into the health effects of air pollution while also seeking ways to reduce health impacts.

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.