Indoor Air Quality

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

Many people spend most of their time indoors. Surprisingly, in some neighborhoods, indoor air has more pollutants than outdoor air. The air we breathe in our homes, schools, and workplaces can lead to health problems. For people with asthma, indoor air pollutants can irritate the airways and cause asthma symptoms.1,2

Secondhand smoke (from other people smoking around you) is a dangerous and common indoor air pollutant. Chemicals from cooking, cleaning, and building are also pollutants.1,3

Keeping indoor air dry and reducing allergens and irritants can help improve air quality. Talk to your doctor about other ways to reduce exposure to indoor air pollutants.1,3

Where does indoor air pollution come from?

Secondhand smoke

Secondhand smoke is released into the air when a smoker exhales. It is also released from a burning cigarette or cigar. Secondhand smoke contains thousands of chemicals. Many of these are toxic airway irritants.4

Exposure to secondhand smoke may directly cause asthma. More research is needed to prove this. But there is a clear link between secondhand smoke and asthma outcomes. Secondhand smoke is especially harmful to young children. For example:1,4-6

  • More than half of children with asthma in the United States are exposed to secondhand smoke
  • Children with asthma exposed to secondhand smoke have more frequent asthma attacks
  • Almost half of children who go to the emergency room for asthma live with smokers
  • Secondhand smoke exposure causes over 200,000 asthma attacks among children every year

Cooking and heating

Cooking and heating appliances can be sources of indoor air pollutants. Burning gasoline, wood, and other fuels can produce harmful gases. These gases can irritate the airways. Some of these gases include:7,8

  • Carbon monoxide
  • Nitrogen dioxide
  • Particulate matter (tiny pieces of dust, dirt, smoke, and other pollutants)
  • Volatile organic compounds (VOCs) (chemicals that evaporate into the air when used)

Housing materials

New construction materials can give off fumes or dust. Old building materials may release pollutants, especially when disturbed. Aging plywood and furniture can contain chemicals that give off gases. Paints, polishes, and carpets can also give off gases. Many of these gases can irritate your airways.9,10

Irritants that come from housing materials include:8,11

  • Asbestos and lead (in older buildings)
  • Formaldehyde
  • VOCs
  • Particulate matter


Cleaning products may contain ingredients that cause health problems. These include VOCs and other dangerous chemicals. These chemicals can irritate the airway and contribute to ongoing (chronic) airway problems. Cleaning products that may contain VOCs include:12

  • Aerosol spray products
  • Air fresheners
  • Detergents
  • Rug cleaners

Dampness and allergens

Dampness and humidity promote the growth of common indoor allergens. Exposure to these allergens can trigger reactions and asthma symptoms. These allergens include:13-15

  • Dust mites
  • Mold
  • Cockroaches
  • Rodents

These allergens exist everywhere. Even homes without cockroaches may have cockroach allergens in dust and fabrics. Keeping dampness and humidity low can reduce the levels of these allergens.13

How can I improve indoor air quality?

Improving indoor air quality is a great way to reduce exposure to asthma triggers. Indoor air quality tends to be worse in urban and densely populated areas. These areas have more sources of pollution. The pollution sources may also be harder to control.1,16,17

The best ways to reduce indoor air pollution are to:1,4,16

  • Avoid smoking indoors
  • Reduce moisture and humidity levels
  • Keep windows closed on days with air quality alerts

Some other ways to improve indoor air quality include:1,7,16

  • Make sure appliances are vented to the outdoors
  • Do not use ovens or gas ranges to heat the home
  • Do not burn charcoal or kerosene inside
  • Install a carbon monoxide detector
  • Use paints and other supplies that are low in VOCs
  • Ensure extra airflow when using products that may have VOCs
  • Wait before bringing new carpet or fresh dry cleaning into the home

Keep down dampness and allergens by:1,7,16

  • Using air filters or purifiers
  • Dusting regularly
  • Removing or regularly cleaning upholstered furniture, drapes, carpets
  • Washing bedding in hot water once a week
  • Regularly cleaning places where mold can grow
  • Fixing leaks and plumbing problems quickly
  • Cleaning the kitchen often, especially places where food can get trapped

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