Indoor Air Quality: Everything You Need to Know

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Maybe you have a habit of checking the air quality in your area before you head out for your morning walk, but how much do you know about indoor air quality? From firing up your gas stove to cook dinner to lighting candles while you read, a lot of human activities impact our indoor air quality. Plus, outdoor air pollution from things like traffic or wildfires can also impact the air inside our homes.

Indoor air quality (IAQ) is the quality of air inside structures, and air quality can degrade in the presence of pollutants. Particulate matter, like dust and mold, can worsen air quality. Breathing in pollutants is of concern because of the potential impacts on human health.

So where is all that pollution coming from? Even if you like to "air out" the house by opening some windows, you’ll find that everything from household appliances to carpets to wall paint can impact indoor air quality.

Anything that combusts or produces smoke can leave pollutants in its wake. Wood-burning stoves, present in some homes to provide warmth, are a major source of particle pollution and release carbon monoxide, carbon dioxide, nitrogen oxides, and other pollutants that are harmful to human health. Other sources of combustion and smoke can include lit candles, cigarettes, and fireplaces. If you live in an area prone to wildfires, the smoke from those events can also infiltrate your home and worsen IAQ.

Many household materials emit harmful gases called volatile organic compounds, or VOCs. VOCs are present in building materials, like flooring, paint, and caulk, but they can also be emitted by everyday household items, like cleaners, air fresheners, and cosmetics. Carpets and rugs, craft supplies, and even furniture can release VOCs into the air. In fact, the U.S. Environmental Protection Agency (EPA) found that levels of several common VOCs are up to five times higher indoors than outside.

We love our pets, but it's important to note that they can contribute to poorer IAQ because of pet dander and fur. Mammals can shed pet dander, and it goes airborne, leaving these microscopic particles all over the home and in the air. For some people, pet dander can trigger an allergic reaction and cause difficulty breathing, watery eyes, runny nose and itchy skin. Pet dander can also worsen asthma symptoms.

Many people know that mold isn't something to allow as a houseguest. But why? Mold and mold spores are often highly dangerous, and they can trigger severe allergy symptoms in humans. Mold can irritate the skin, eyes, nose and throat, even for people who are not severely allergic to mold. Like other indoor air pollutants, mold spores can also trigger asthma attacks. In addition to releasing allergens and irritants, mold may also release mycotoxins, which are linked to a range of short- and long-term health issues such as acute poisoning, immune deficiency and cancer.

For homes in industrial areas, wildfire-prone regions or even big cities with high amounts of traffic, pollution generated outdoors can also impact the air quality inside, too. When you open up doors and windows, you can let in outdoor air pollutants. But even without opening the doors and windows, pollutants can get inside through the tiniest cracks and gaps around a building.

Indoor air quality is determined by various different pollutants, from tiny particles of pet dander or mold spores to harmful gases like carbon monoxide or nitrogen oxides. When it comes to indoor air pollution, some of the common air pollutants include VOCs, ozone, particulate matter and sulfur dioxide.

Particulate matter comes in different sizes. Coarse particulate matter, or PM10, are smaller than a piece of hair, and include pollutants like mold, pollen or dust. Fine particulate matter, or PM2.5, are even smaller and more dangerous to human health. PM2.5 includes smoke from tobacco products, stoves, fireplaces and candles. Then, there are ultra-fine particles, sometimes called PM0.1, which can come from natural gas emissions, vehicle exhaust, cooking, vacuuming and even using printers and other office machines. The small size of these particles make them the most dangerous, because they are easily inhaled and can travel into the lungs and through the bloodstream.

Many homes have carbon monoxide to warn of dangerous levels of this deadly pollutant. Carbon monoxide is odorless and colorless, but highly potent and toxic. This indoor air pollutant can come from sources of combustion, like furnaces, gas-powered water heaters, fireplaces, generators, vehicle exhaust and cigarette smoke. Carbon monoxide causes carboxyhemoglobin to form in the blood, inhibiting oxygen intake. Inhaling this gas can lead to chest pain, fatigue and reduce brain function at low to moderate exposures, while it can cause headaches, flu-like symptoms, confusion and dizziness at high concentrations and can be fatal.

Volatile organic compounds, or VOCs, are common in many household products and materials. They evaporate at room temperature and contribute to poor indoor air quality. You can find VOCs in paints, carpeting, pressed wood and other flooring materials, household cleaners, furnishings and even craft supplies, like markers and glues. Exposure to VOCs can lead to health impacts ranging from irritation of the eyes, nose and throat to liver, kidney and/or central nervous system damage. Some VOCs are also carcinogenic.

Nitrogen oxides, which occur when fuel burns at high temperatures, are poisonous and highly reactive. These gases typically come from vehicle emissions, but may also be emitted at power plants, making homes near these facilities more vulnerable to exposure. Exposure to nitrogen oxides can cause irritation to the respiratory system, or can worsen symptoms of people with existing respiratory diseases. Longer exposures to nitrogen oxides may cause asthma.

Like nitrogen oxides, sulfur dioxide is emitted as fossil fuels are burned. The major sources of sulfur dioxide emissions are industrial facilities, including power plants, metal processing and diesel-burning vehicles. Difficulty breathing, reduced lung functioning and worsening asthma symptoms can occur with sulfur dioxide exposure. High sulfur dioxide emissions can also produce sulfur oxides, which can form harmful particulate matter when reacting to other compounds in the air.

Ozone, also known as ground-level ozone or O3, is one of the main components of what we know as smog. Ozone that occurs naturally in the stratosphere is beneficial, as it shields Earth from UV rays. But ground-level ozone is caused from chemical reactions of other air pollutants, nitrogen oxides and VOCs, in sunlight. Exposure to ozone may cause coughing, difficulty breathing, damaged airways and weakened lungs. It can also worsen lung conditions such as asthma, emphysema and chronic bronchitis.

Each individual air pollutant is linked to various poor health impacts. So when we are exposed to multiple types of air pollution, often at higher concentrations when indoors, the health implications may be amplified.

One of the earliest symptoms of exposure to poor indoor air quality is irritation to the eyes, nose, throat, respiratory system or skin. These symptoms may show with smaller amounts of air pollution present indoors or during short-term exposures.

When IAQ is affected by pollutants like pet dander, pollen, dust or smoke, these pollutants may trigger allergic reactions in people. Responses can include rhinitis, wheezing and bronchospasm, which can limit oxygen intake in the body.

Longer exposures to indoor air pollution can lead to respiratory illnesses. According to World Health Organization, about 3.2 million people die prematurely from illnesses that can be linked to indoor air pollution, specifically from incomplete combustion of fuels during cooking. Of those premature deaths, 21% are from lower respiratory infections.

Poor indoor air quality isn't just an issue for the lungs and the rest of the respiratory system. Air pollutants can also cause problems for the human heart. Over one million people die prematurely each year from ischaemic heart disease attributed to indoor air pollution exposure, WHO reported. Ischaemic heart disease is when arteries are narrowed, making it so that less blood and oxygen make it to the heart, the American Heart Association explained. This disease, also known as coronary heart disease, can lead to a heart attack.

The lungs are the crucial component of the respiratory system, so in addition to other respiratory illnesses, poor IAQ is linked to multiple impacts on the lungs. Many pollutants, including nitrogen oxides and fine particulate matter, have been linked to asthma development. A 2021 analysis of 49 studies found that exposure to VOCs presented a moderate risk for developing pulmonary diseases, such as asthma and chronic obstructive pulmonary disease (COPD).

Radon, a naturally occurring gas, can build up in homes. Exposure to radon can cause cancer. Radon exposure is a leading cause of lung cancer, but indoor air pollution may also be linked to several other types of cancer. One study found that exposure to fine particulate matter was associated with increased risks of cancers, including cancer in the upper digestive tract, cancers of accessory digestive organs (such as the liver, gall bladder and pancreas) and breast cancer.

According to WHO, there are about 3.2 million deaths linked to household air pollution per year, including over 237,000 deaths of children younger than 5 years old. The organization noted that low- and middle-income countries were most impacted, and women faced the highest burdens of health complications related to poor IAQ.

Carbon monoxide, an especially dangerous pollutant, can also cause premature deaths with high concentrations and long-term exposures. According to the Institute for Health Metrics and Evaluation (IHME), carbon monoxide poisoning led to 41,100 deaths globally in 2019.

Air pollutants can't be completely avoided. Whether you have pets, use a gas stove to cook or live in a big city, there are many factors that can contribute to indoor air pollution. The good news is that there are some steps you can take to minimize your exposure and improve your IAQ.

That urge to "air out" your home in the springtime is actually a great idea for improving IAQ. You can open windows to bring in fresh air, but be mindful that you may let in more outdoor pollution like pollen or dust.

You can also boost your home's ventilation with exhaust fans. If you don't already have them, install exhaust fans, especially over the stove and in high humidity areas (like bathrooms) where mold may grow. If you already have exhaust fans, make sure they are in good working condition, and remember to turn them on when doing activities like using the stove or taking a hot shower.

Make sure to inspect your HVAC system and upgrade the HVAC filters. You may also want to install air purifiers throughout the home, and make sure to change the filters out about every 6 to 12 months.

Because many household materials can emit VOCs, consider shopping for low- or no-VOC products. Consumers can look for products with the UL GREENGUARD Certified label, which means the product has been tested and gone through a one- to six-month certification process to check off gassing levels, and products are retested annually.

If you’ve been considering some kitchen upgrades, now is the time to switch from your gas stove to something electric. Switching from gas appliances can help reduce the amount of emissions in your home. In a pilot program in the Bronx, New York, switching from gas stoves to induction stoves led to up to a 35% decline in nitrogen dioxide pollution indoors, as well as a decrease in the presence of carbon monoxide.

It's easier said than done, but start taking steps to quit smoking tobacco products today to drastically improve indoor air quality. Smoking is a major contributor to indoor air pollution, and smoking and the pollutants this activity releases into your home can lead to major health impacts for you and anyone in your household. One study found that environmental tobacco smoke can increase fine particulate matter 10-fold compared to an idling diesel car in the same time period, showing just how polluting this activity can be. The EPA has also warned that increasing indoor ventilation or even opening windows is not effective in protecting against the impacts of environmental tobacco smoke.

It may seem simple, but another way to improve household air quality is to stop the pollution at its source. If you have a gas stove, fireplace or other combustion source, use them as infrequently as possible. Maybe you can add an electric burner, toaster oven, air fryer, slow cooker or other small electric appliances to your kitchen to cook without gas as much as possible. Instead of storing materials, like paint or spare wood floor boards, in the house, move them to the garage or backyard shed.

Even if cleaning up the house is one of your most dreaded activities, it's important if you want to improve IAQ. Regularly sweeping, vacuuming and mopping can help reduce pollutants like pet dander and dust. Keeping your home clean and well-ventilated will also help keep mold, a common indoor pollutant, at bay.

While they aren't as effective as an air purifying machine and a well-ventilated home, plants may have small impacts on improving indoor air quality. The research is mixed, as some studies have found negligible results of adding plants to a space to remove air pollutants. If you are using pesticides on your plants, you could actually contribute more pollutants. So although opening the windows and changing your air filters are better ways to remove air pollutants, you can still add some indoor plants for better IAQ.

Humans spend most of our time indoors, so what we are breathing inside is just as important to pay attention to as outdoor pollutants. Indoor pollutants are often in much higher concentrations compared to outdoors because they are confined in smaller spaces, making their exposure worse on our health.

Poor air quality can contribute to various health complications, and the longer the exposure, the higher the risks. With links to heart and lung diseases and cancers, indoor air pollutants must be taken seriously. At the individual level, that can mean taking action to minimize sources of pollution indoors while also increasing household ventilation to improve IAQ.

But companies will also need to work toward manufacturing products that emit less pollutants, and governments will need to continue to set and enforce strict standards when it comes to pollutants.

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