Radon

A colorless, odorless gas that can seep into your home from the ground, radon is often referred to as the second most common cause of lung cancer behind smoking.
What to look for: Basements or any area with protrusions into the ground offer entry points for radon. The Environmental Protection Agency publishes a map of high-prevalence areas. A radon test can determine if high levels are present.

Asbestos

A fibrous material once popular as fire-resistant insulation, asbestos was banned in 1985. However, it’s often found in the building materials, floor tiles, roof coverings, and siding of older. If disturbed or damaged, it can enter the air and cause severe illness.
What to look for: Homes built prior to 1985 are at risk of having asbestos in their construction materials. Home owners should be careful when remodeling because disturbing insulation and other materials may cause the asbestos to become airborne.

Lead

This toxic metal used in home products for decades can contribute to several health problems, especially among children. Exposure can occur from deteriorating lead-based paint, pipes, or lead-contaminated dust or soil.
What to look for: Homes built prior to 1978 may have lead present. Look for peeling paint and check old pipes. To get a HUD-insured loan, buyers must show a certificate that their older home is lead-safe.

Other hazardous products

Stockpiles of hazardous household items — such as paint solvents, pesticides, fertilizers, or motor oils — can create a dangerous situation if not properly stored. They can easily spark fires and can cause illness or even death if ingested, even in small amounts.
What to look for: Check all the corners, crawl spaces, garages, or garden sheds in the home. If these products are found, make sure you ask for their removal and get a disposal certificate prior to closing.

Groundwater contamination

When hazardous chemicals are disposed of improperly, they can seep through the soil and enter water supplies. A leaking underground oil tank or septic system can contribute to this.
What to look for: Homes near light industrial areas or facilities may be at risk, as are areas once used for industry that are now residential.

Source: National Association of REALTORS®