For many people, air pollution is an outside thing—think exhaust spewing from cars or factory chimneys belching smoke—not something that happens inside our ordered, cozy homes. But according to the Environmental Protection Agency (EPA), the surprising truth is the air inside our homes might be up to five times more polluted than the air outside. (1) Combine that with research that suggests people spend roughly 90 percent of their time indoors and you have a perfect storm of why air pollution can lead to significant health conditions. (2) In 2014, a World Health Organization (WHO) report stated air pollution had become the world’s single biggest environmental health risk, linked to around 7 million deaths in 2012. (3)

Indoor air pollution

The issue is even more insidious because you can’t see air pollution with the naked eye—a lack of smog is no indication of purity. And despite all our attempts to keep our indoor spaces tidy, ultimately it takes more than cleanliness to improve indoor air quality.

In the last decade, a growing body of research confirms that even in the largest and most industrialized cities, the pollution in the home can far exceed what’s outside it. (4)

Curious about the main causes of indoor air pollution?

Carcinogens such as radon and formaldehyde, as well as impurities such as pollen, dust mites, pet dander, plus a variety of particulate matter, created when we burn candles or cook are all major contributing factors.

Woman cleaning high shelf with duster

Regardless of our attempts to keep our indoor spaces tidy, ultimately it takes more than cleanliness to improve indoor air quality.

The changing seasons can be a contributing influence as well. In winter and colder months, when windows stay closed, hampering ventilation, indoor air pollution levels can soar. The lack of ventilation increases indoor pollutant levels because there’s no outdoor air to dilute indoor emissions, nor do indoor air pollutants have the chance to be carried out of the home.

9 most common indoor air pollutants

When certain air pollutants from particles and gases contaminate indoor air, it can escalate into indoor air pollution. The following are the most significant causes of indoor air pollution. (5)

1. Asbestos

Asbestos is found in various materials used in home construction such as coatings, paints, building materials, and ceiling and floor tiles. Since 1989 asbestos has been partially banned partially in the U.S., so it’s much less of a threat in houses built since then. (6) However, in homes built before 1989, the risk of asbestos is substantial.

2. Formaldehyde/Pressed wood products

Formaldehyde is an important chemical used widely by industry to manufacture building materials and numerous household products such as paints, sealants, and pressed wood products. In 2018, it became illegal to manufacture or import composite wood products in the United States if they contain excessive amounts of formaldehyde. (7) Formaldehyde is also a by-product of combustion, such as cigarette smoke and cooking. Formaldehyde tends to be omnipresent, indoors and outdoors, at low levels. In higher concentrations and sustained exposure, formaldehyde can cause irritation of the skin, eyes, nose, and throat as well as cause some types of cancers.

Did you know?
Formaldehyde is actually naturally occurring in our environment—and our bodies. It’s found in trace amounts in every living system, including fruits and vegetables. According to the American Chemistry Council, “Humans produce about 1.5 ounces of formaldehyde a day as a normal part of our metabolism”. (8)

3. Radon

Radon is a naturally occurring radioactive gas that can be found underneath your home in various types of bedrock and other building materials. When trapped inside buildings, it can be a cause of indoor air pollution. Radon can get into the walls of your home and can significantly increase your chances of developing lung cancer. (9)

4. Tobacco smoke/secondhand smoke

Tobacco smoke is one of the most toxic indoor air pollutants. Secondhand smoke, also called environmental tobacco smoke or passive smoking, is a mixture of the smoke given off by the tobacco products, including cigarettes, cigars or pipes along with the smoke exhaled by smokers. Tobacco smoke is considered one of the most deadly carcinogens— it contains more than 7,000 chemicals, many of them toxic. (10) Exposure to secondhand smoke is much more dangerous when it occurs indoors, particularly in homes and cars.

5. Carbon monoxide

Carbon monoxide, an odorless, colorless and toxic gas, can kill you in high enough doses. Wood stoves, space heaters, and fireplaces, all emit carbon monoxide as well as nitrogen dioxide. Leaking chimneys and furnaces, generators, and gas stoves are also common sources of carbon monoxide in the home. The problem with carbon monoxide poisoning is that its symptoms are very similar to the flu—headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion—so people often don’t realize they’ve been poisoned. (11)

6. VOCs

Volatile organic compounds (VOCs) include a huge gamut of potentially harmful chemicals that worsen indoor air pollution and can even lead to cancer. (12) In addition, they can react with other gases and form other air pollutants after they are in the air. Paints, varnishes, wax, adhesives, caulks, and sealants all contain organic solvents that can impact breathing. Many cleaning, disinfecting, cosmetic, degreasing, and hobby products also increase your home’s pollution load. Fuels, such as gas and kerosene, are made up of VOCs as well.

Did you know?
Products containing VOCs release organic compounds while you are using them, but did you know many of them continue to release VOCs even when they are simply being stored? As volatile compounds, by definition, they are unstable, which means unused chemicals stored in the home can sometimes “leak” and release VOCs into the air. (13)

7. Biological contaminants

Biological contaminants refer to microorganisms that infiltrate our indoor environments, such as bacteria, viruses, fungi, and parasites. In our home, these kinds of contaminants manifest as animal dander and cat saliva, house dust mites, cockroaches, insects, pollen, mold, and mildew. Standing water, water-damaged materials or wet surfaces are the biggest culprits responsible for bacteria of all kinds: The moisture serves as a breeding ground for molds, mildews, bacteria, mites, and insects. Prolonged exposure to biological pollutants can cause sneezing, watery eyes, coughing, shortness of breath, dizziness, lethargy, fevers. (14)

8. Pesticides

Inherently toxic, pesticides are chemicals that are used to kill or control pests. They include disinfectants, insecticides, fungicides, and rodent and termite poison. Sold as sprays, liquids, sticks, powders, crystals, balls, and foggers, chronic exposure to some pesticides can damage your liver, kidneys, and endocrine and nervous systems. (15)

Did you know?
According to a study published in Pediatrics, in 2008, pesticides were the ninth most common substance reported to poison control centers, and approximately 45 percent of all reports of pesticide poisoning were regarding children. (16)

Man cleaning kitchen counter with gloves on

Many household cleaning products, such as limonene, can be a factor in increasing indoor pollution.

9. Household cleaning and personal care products

Cleaning supplies can be an underestimated source of VOCs in your home. For example, a study published in Environmental Science & Technology found when bleach combines with a common citrus ingredient called limonene, it creates higher concentrations of toxic emissions. (17) Then there are the ubiquitous air fresheners, which emanate their own potent bouquet of toxins.

One study found they emit over 100 different chemicals that react to each other and form new combos of pollutants. (18) Personal care products, particularly perfume and nail polish, are largely unregulated. They are responsible for a great deal more air pollution than many realize. A recent study found that domestic VOCs present in lotions, paints, and other household products contribute about as much to air pollution as motor vehicle emissions.These VOCs cause serious eye and nose irritation, and can possibly stimulate as asthma attack. In the long-term, VOC exposure can cause liver, kidney and central nervous system damage, and cancer. (19)

The effect of indoor air pollution on your health

Health effects from indoor air pollutants may be experienced immediately upon exposure or potentially years later. The immediate effects, often short-lived, can include irritation of the eyes, nose and throat, headaches, dizziness, and fatigue. Sometimes the solution is simply to eliminate exposure to the pollutant in question if you can determine the source. But many chronic exposures can result in more long-term effects, such as respiratory diseases, heart disease, and cancer. Asthma, hypersensitivity pneumonitis and humidifier fever, a viral lung inflammation triggered by humidifier-bred bacteria, can be caused—or worsened—by some indoor air pollutants. (20)

10 ways to improve indoor air quality

It’s impossible to get completely clean air. Walking, cleaning, cooking can all add low levels of contaminants. But you can do multiple things, from structural to easy fixes, that can keep your indoor air safer. And while air purifiers seem like an obvious solution, their health benefits are widely overrated. At their best, they can modestly reduce allergy symptoms, but their efficacy for asthma attacks has less scientific support. (21)

According to the EPA, by far the most effective method to minimize indoor air pollution is to control the sources of pollutants and to ventilate a home with clean outdoor air when possible. (22) Here are some of the EPA’s most viable strategies for caring for your indoor air.

Did you know?
Chalk it up to urban myth, but plants don’t actually remove pollutants from the air. Claims have been made suggesting that potted plants may reduce indoor VOC concentrations, but those studies mainly took place in small, sealed chambers over many days. More recent studies show that a plant’s purification prowess does not impact indoor VOC levels. (23)

Steam rising from humidifier in kitchen.

Using a humidifier to control the relative humidity level in your home is a good option to keep indoor air clean.

1. Use a dehumidifier

Controlling the relative humidity level in a home can help minimize certain kinds of bacteria. Relative humidity of 30-50 percent is considered ideal for homes. (24) Make sure to clean your dehumidifier in accordance with the manufacturer’s instructions and refill with clean water daily. For sensitive people, studies do show a link between indoor dampness and some upper respiratory tract symptoms, coughing, wheezing, and asthma symptoms. (25)

2. Resolve your radon

Test for radon and seek ways to mitigate it if there is a problem. If you know through testing that your home exceeds the recommended radon level, the first step is to choose a qualified radon mitigation contractor to reduce your home’s radon level. It’s a fairly common problem that can definitely be minimized and lived with if fixed. Some radon reduction systems have a 99 percent reduction success rate. (26)

3. Be vigilant about ventilation

Always ventilate your space when using products with chemicals that can release pollutants into the air; if products are stored following use, make sure to close tightly. Many household cleaners contain chemicals that are corrosive to the lungs and can cause respiratory damage. (27)

4. Minimize mold and mites

Reduce asthma triggers such as mold and dust mites. Keep all areas in the home clean and dry, especially carpets. Empty water trays in air conditioners, dehumidifiers and refrigerators frequently. Clean up any mold, which can lead to respiratory illnesses, and get rid of excess water or moisture. (28)

5. Put the kibosh on smoking

Introduce a zero-tolerance policy for indoor smoking. Indoor tobacco smoke can increase your risk of heart attacks, even if you are a non smoker. One of the most important things you can do for your health is to ensure a smoke-free home. (29)

6. Keep a tight leash on leaks

Inspect fuel-burning appliances regularly for leaks; make repairs when necessary. Unlike carbon monoxide, gas leaks have a warning smell so that it can be readily detected. A gas leaks can make you feel dizzy, nauseous and experience difficulty breathing, and in large amounts can cause suffocation. (30)

7. Beware of carbon monoxide

While smoke detectors alert you to the presence of smoke and possibly fire in your home, carbon monoxide detectors alert you to dangerous levels of carbon monoxide gas. It may be worthwhile to invest in a carbon monoxide alarm or purchasing a combo detector. (31)

8. Put VOCs in their place

To avoid developing a respiratory-based health issue or worsening asthma, store unused chemicals in a garage or shed where people do not frequent. (32)

9. Become an eco-conscious cleaner

Check the ingredients of your cleaning supplies to make sure they are low VOC and non-toxic. Stay clear of ingredients such as formaldehyde,1,4-Dioxane, and quaternary ammonium compounds, or “quats,” which often appear on the label as benzalkonium chloride. (33) Quats function as germ killers in antibacterial cleaning supplies and disinfectants, but are also a recognized lung irritant. (34)

10. Get the facts on new furniture

According to the EPA, purchasing “exterior-grade” pressed-wood products are a smart way to limit formaldehyde exposure in the home. (35) These products off-gas less formaldehyde than cheaper pressed wood products because they contain phenol resins, as opposed to the more lethal urea resins. Before buying pressed-wood products, such as cabinetry and furniture, ask about or research the formaldehyde content of these products.

The bottom line

These small changes you make within the home can seem insignificant, but when you add them all together, they make a big difference, enhancing your indoor air quality—and your long-term health.

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