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Indoor Air Quality

Indoor Air Quality

We tend to think of air pollution as a risk faced outside, but the air we breathe indoors can also be polluted. Smoke, vapors, mold, and chemicals used in certain paints, furnishings, and cleaners can all affect indoor air quality and our health.

Buildings affect overall well-being because most people spend most of their time inside. The U.S. Environmental Protection Agency estimates Americans are indoors 90% of their time –in built environments such as homes, schools, workplaces, places of worship, or gyms.

Environmental health researchers study how indoor air quality affects human health and well-being. Studies suggest that indoor concentrations of air pollutants are increasing, driven by factors such as the types of chemicals in home products, inadequate ventilation, hotter temperatures, and higher humidity.

Indoor air quality is a global issue. Both short- and long-term exposure to indoor air pollution can cause a range of health issues, including respiratory diseases, heart disease, cognitive deficits, and cancer. As one prominent example, the World Health Organization estimates 3.8 million people (https://www.who.int/health-topics/air-pollution#tab=tab_3) worldwide die every year from illnesses attributable to harmful indoor air from dirty cookstoves and fuel.

Certain populations may be affected more than others. Children, older adults, individuals with preexisting conditions, Native Americans, and households of low socioeconomic status are often exposed to higher levels of indoor pollutants

Types of Pollutants

Many factors contribute to poor indoor air quality. Indoor air includes pollutants that penetrate from the outdoors, as well as sources that are unique to the indoor environment. These sources involve:

  • Human activities within buildings, such as smoking, burning solid fuels, cooking, and cleaning.
  • Vapors from building and construction materials, equipment, and furniture.
  • Biological contaminants, such as mold, viruses, or allergens.

Some contaminants are described below:

  • Allergens (https://www.nih.gov/health/topics/agents/allergens/index.cfm) are substances that can trigger the immune system, causing an allergic reaction; they can circulate in air and remain on carpets and furniture for months.
  • Asbestos is a fibrous material formerly used for making incombustible or fireproof building materials, such as roof shingles, siding, and insulation.
  • Disturbing asbestos minerals or asbestos-containing materials can release fibers, often too small to see, into the air. Asbestos is known to be a human carcinogen.
  • Carbon monoxide is an odorless and toxic gas. It is found in fumes produced any time you burn fuel in cars or trucks, small engines, stoves, lanterns, grills, fireplaces, gas ranges, or furnaces. Proper venting or exhaust systems prevent build up in the air.
  • Formaldehyde (https://www.nih.gov/health/topics/agents/formaldehyde/index.cfm) is a strong-smelling chemical found in some pressed wood furniture, wood particle cabinets, flooring, carpets, and fabrics. It can also be a component of some glues, adhesives, paints, and coating products. Formaldehyde is known to be a human carcinogen.
  • Lead (https://www.nih.gov/health/topics/agents/lead/index.cfm) is a naturally occurring metal that has been used in a wide variety of products including gasoline, paint, plumbing pipes, ceramics, solders, batteries, and even cosmetics.
  • Mold (https://www.nih.gov/health/topics/agents/mold/index.cfm) is a microorganism and type of fungus that thrives in damp places; different molds are found everywhere, indoors and outside.
  • Pesticides (https://www.nih.gov/health/topics/agents/pesticides/index.cfm) are substances used to kill, repel, or control certain forms of plants or bugs that are considered to be pests.
  • Radon (https://www.nih.gov/health/topics/agents/radon/index.cfm) is a colorless, odorless, naturally occurring gas that comes from the decay of radioactive elements in soils. It can enter indoor spaces through cracks or gaps in buildings. Most exposures occur inside homes, schools, and workplaces. EPA estimates radon is responsible for about 21,000 U.S. deaths from lung cancer annually
  • Smoke (https://www.nih.gov/health/topics/agents/allergens/smoke/index.cfm) , a byproduct of combustion processes, such as from cigarettes, cookstoves, and wildfires, contains toxic chemicals like formaldehyde and lead.

Respiratory Disease

  • Actions to reduce mold exposure in early life may have long-term health benefits, potentially decreasing prevalence and severity of asthma.
  • Among inner-city children with asthma who live in homes with high levels of indoor air pollution, those children with sufficient vitamin D levels had fewer symptoms.
  • Household air pollution exposure likely affects lung development prenatally. Indoor air pollution exposure during pregnancy was associated with impaired lung function in infants. This altered infant lung function may then increase risk for pneumonia in the first year of life.
  • Outdoor air quality can affect indoor air. Air pollution levels have been trending downward over several decades in southern California, due to air quality-control policies. These improvements in air quality are associated with improved lung development in children.
  • The school environment contributes to childhood asthma illness. A study found that airborne mouse allergens in inner-city schools are linked to increased symptoms and decreased lung function in asthmatic children. School-based environmental interventions may be beneficial for curbing the public health problem of childhood asthma.

Cardiovascular Disease

A study partially supported by NIEHS found that markers of cardiovascular disease risk appear when ozone levels are even lower than current EPA air quality standards. In healthy adults, exposure to short-term indoor and outdoor ozone was linked to increased blood platelets, a risk factor for clotting, and increased blood pressure.

Cognitive Effects
  • Indoor exposures to air pollutants, including particulate matter, allergens, oxides of nitrogen, endotoxin, and mold, have been associated with impaired health and performance in children and adults
  • Characterization of indoor air pollution in schools is a public health concern for children, given the large amount of time spent there. Some inner-city schools exceeded WHO guidelines for interior air quality, particularly for nitric oxide, an indoor air pollutant that can affect cognitive outcomes, verbal abilities, and executive functioning. Physical defects and lack of proper ventilation contributed to the poor air quality in schools. The results suggest that improving building conditions and facilities, as well as consideration of the school’s outdoor surroundings, could create healthier environments.
  • Office workers scored higher on performance measures when working in “green” environments with low indoor pollutants and low carbon dioxide levels.
  • The air quality within an office can affect employees’ cognitive function, including response times and ability to focus, and it may also affect their productivity, according to NIEHS-funded research led by Harvard T.H. Chan School of Public Health.
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  • Cancer Long-term exposure to radon and other indoor air substances that increase the chance of developing lung cancer include secondhand smoke, asbestos, arsenic, and some forms of silica and chromium.
  • Indoor air contaminants, such as the carcinogen formaldehyde, exceed acceptable levels in some early childhood learning centers
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