| Radon source | Natural uranium decay in soil and rock beneath your home (U.S. Environmental Protection Agency (EPA)) |
| Radon health risk | Leading cause of lung cancer in non-smokers in the U.S. (EPA Radon Guide) |
| EPA radon action level | 4 picocuries per liter (pCi/L) or higher (EPA) |
| Carbon monoxide (CO) source | Incomplete combustion from furnaces, water heaters, gas stoves, vehicles (Consumer Product Safety Commission (CPSC)) |
| CO detector placement | Every sleeping area and on every level of the home (National Fire Protection Association (NFPA)) |
| Common VOC sources | Paints, adhesives, cleaning products, new flooring, pressed wood (EPA Indoor Air Quality resources) |
| VOC exposure risk | Eye/throat irritation, headaches, dizziness; long-term exposure may be more serious (EPA) |
| Ventilation role | Dilutes and removes indoor pollutants by introducing fresh outdoor air (ASHRAE Standard 62.2) |
Three Threats You Cannot See, Smell, or Taste
Most homeowners are aware that the air outside can carry pollution. Fewer realize that the air inside their homes often carries its own invisible hazards — and that those hazards can build up quietly over years. Radon, carbon monoxide (CO), and volatile organic compounds (VOCs) are three of the most important to understand. Each has a different origin, a different health concern, and a different response — but all three share one critical trait: you cannot detect any of them without the right tools.
If you spend a significant amount of time at home — as many adults over 50 do — your exposure to whatever is in your indoor air is higher than average. That makes awareness and simple precautions especially worthwhile. For a broader look at what shapes indoor air quality, see our plain-language indoor air quality guide.
Testing Is the Only Way to Know
None of these three hazards — radon, carbon monoxide, or VOCs — have any color, smell, or taste. Symptoms of exposure are often mistaken for the flu, fatigue, or allergies. Relying on how you feel rather than how you test is a common and avoidable mistake. Detection devices and professional testing are the only reliable way to know what is in your air.
Radon: A Gas That Rises From the Ground
What it is: Radon is a naturally occurring radioactive gas produced when uranium in soil, rock, and water breaks down. It seeps up through the ground and can enter your home through cracks in foundations, gaps around pipes, and other openings at or below ground level.
Why it matters: Radon is the leading cause of lung cancer among people who have never smoked, according to the U.S. Environmental Protection Agency. The risk accumulates over years of breathing elevated concentrations indoors.
What to do: Test your home. Short-term test kits (available at hardware stores) give a rough reading in two to seven days. Long-term tests, left in place for 90 days or more, give a more accurate picture of your average exposure. If results come back at or above 4 picocuries per liter (pCi/L), the EPA recommends taking action. Radon mitigation systems — typically a pipe and fan installed by a certified contractor — can reduce levels significantly. This is not a DIY project; professional installation and post-mitigation testing are strongly recommended.
| Radon source | Natural uranium decay in soil and rock beneath your home (U.S. Environmental Protection Agency (EPA)) |
| Radon health risk | Leading cause of lung cancer in non-smokers in the U.S. (EPA Radon Guide) |
| EPA radon action level | 4 picocuries per liter (pCi/L) or higher (EPA) |
| Carbon monoxide (CO) source | Incomplete combustion from furnaces, water heaters, gas stoves, vehicles (Consumer Product Safety Commission (CPSC)) |
| CO detector placement | Every sleeping area and on every level of the home (National Fire Protection Association (NFPA)) |
| Common VOC sources | Paints, adhesives, cleaning products, new flooring, pressed wood (EPA Indoor Air Quality resources) |
| VOC exposure risk | Eye/throat irritation, headaches, dizziness; long-term exposure may be more serious (EPA) |
| Ventilation role | Dilutes and removes indoor pollutants by introducing fresh outdoor air (ASHRAE Standard 62.2) |
Carbon Monoxide: The Product of Incomplete Combustion
What it is: Carbon monoxide forms whenever fuel — gas, oil, propane, wood, or charcoal — burns incompletely. Common sources in homes include furnaces, boilers, water heaters, gas stoves, fireplaces, and attached garages where vehicles idle.
Why it matters: CO displaces oxygen in the bloodstream. At low concentrations it causes headaches, dizziness, and nausea — symptoms easily confused with the flu. At high concentrations it can be fatal. Older adults, people with heart conditions, and anyone with reduced lung capacity face greater risk at lower exposure levels.
What to do: Install UL-listed CO detectors on every level of your home and in or near every sleeping area. Test them monthly and replace them according to the manufacturer's schedule — most detectors have a service life of five to seven years. Have fuel-burning appliances inspected annually by a qualified technician. Never run a vehicle, generator, or charcoal grill inside an attached garage, even with the door open. For a deeper look at heating system safety, see our article on heating your home safely.
VOCs: Chemical Gases From Everyday Products
What they are: Volatile organic compounds (VOCs) are gases emitted by a wide range of common household products and materials. Sources include paints, varnishes, adhesives, cleaning products, air fresheners, new carpeting, pressed-wood furniture, and certain building materials. The term covers hundreds of individual chemicals; formaldehyde is one of the most commonly discussed.
Why they matter: Short-term exposure can cause eye, nose, and throat irritation, headaches, and dizziness. Some VOCs are classified as probable or known carcinogens with long-term exposure. Tightly sealed, energy-efficient homes — which conserve heat well — can trap VOCs at higher concentrations indoors. Our article on hidden pollutants in tightly sealed homes covers this dynamic in more detail.
What to do: Improve ventilation when using products that emit VOCs — open windows, run exhaust fans. Store chemical products in a garage or shed rather than indoors. When replacing flooring, cabinetry, or furniture, look for low-VOC or no-added-formaldehyde labeling. Allow new materials to off-gas in a well-ventilated space before installation where possible. Mechanical ventilation systems help continuously dilute indoor pollutants; our guide on what home ventilation actually does explains how those systems work.
This article is for informational purposes only. It does not substitute for professional testing, inspection, or advice from a licensed contractor or certified indoor air quality specialist. Always verify local codes and requirements with a qualified professional.