We all know that outdoor air pollution can be hazardous to our health, but indoor air quality presents several risks that we should keep top of mind as well. Sources such as heating systems, certain building materials and even nature itself can release harmful gases or particles into the air inside our homes, according to the Environmental Protection Agency (EPA). And inadequate ventilation can lead to increased concentrations and exposure.

Here’s a look at three common indoor air pollutants and what you can do to avoid unsafe levels in your home:

Carbon Monoxide
Carbon monoxide is an odorless, colorless gas. Common sources of carbon monoxide include improperly vented gas appliances, poorly maintained boilers and furnaces, and clogged or leaking chimneys. Carbon monoxide can be fatal at high concentrations. And at lower concentrations, it may cause fatigue, nausea, headaches, impaired vision and reduced brain function, among other symptoms.

To prevent high concentrations of carbon monoxide, it’s important to properly maintain all combustion equipment and ensure proper ventilation. (The EPA recommends having a trained professional inspect chimneys, water heaters, gas furnaces, and gas ranges and ovens annually.) It’s also important to keep a carbon monoxide detector in good working order in your home.

Radon is a radioactive gas that results from the natural breakdown of uranium in soil, rock and water. Like carbon monoxide, it is both odorless and colorless. All homes, new and old, are susceptible to radon. The gas typically enters a home by rising up through the soil and seeping into the cracks and crevices of a home’s foundation, but it may also enter the home through wall cracks, construction joints and water supply sources, among other areas. The EPA estimates that one in 15 homes in the United States is affected by high levels of radon.

Exposure to elevated radon levels is known to cause lung cancer and serious respiratory health issues. The best way to ensure that your home is safe is to administer a radon test. You may either hire a qualified testing professional or purchase a home kit to test your home for radon. There are both short- and long-term tests available. The EPA recommends starting with a short-term test. The results of this test will indicate whether you should follow up with another short-term test or a long-term test. The higher the results, the greater the likelihood that you’ll need to hire a radon mitigation specialist to address the problem.

Volatile Organic Compounds
Volatile Organic Compounds (VOCs) are emitted as gases from a variety of household paints, disinfectants and solvents, as well as some building materials – including certain carpets and flooring. The health effects of VOC exposure will depend on the level of exposure and the amount of time exposed, but VOCs are known to cause eye, nose and throat irritation; headaches; nausea; damage to the liver, kidney and central nervous system; and, in some cases, even cancer.

To decrease exposure to VOCs in your home, the EPA recommends carefully following label instructions, increasing ventilation when using VOC-emitting products, and safely storing and disposing of unneeded chemicals. Many products offer low-VOC or zero-VOC options; it’s best to choose these whenever possible.

To evaluate your risk for poor indoor air quality, take a survey of your home. Identify where combustion systems are located, inventory how chemicals are stored and assess whether ventilation is adequate. If you’d like further reassurance that your home is safe, contact your local health department for guidance on how to evaluate your home’s air quality with the help of professionals.

By Megan Linhoff, Angie’s ListMegan Linhoff is a reporter for Angie’s List, a trusted provider of local consumer reviews and an online marketplace of services from top-rated providers. Visit AngiesList.com.