Asbestos can become a hazard to health if it is in a location where it might become airborne and breathed. It is a carcinogen if sufficient quantities are inhaled over time. There is no cure for mesothelioma lung cancer.
Asbestos was heavily used in older home construction, particularly in vinyl floor coverings, ceiling insulation, "popcorn" ceiling treatments, exterior siding and roofing.
When used in ceiling insulation, asbestos can become a hazard if particles sift down through cracks or damaged areas or if portions of ceiling are disturbed for remodeling. Pressure changes can suck particles into the home.
Flooring that contains asbestos is dangerous because particles become airborne due to wear as people walk on the flooring. If the asbestos containing flooring is covered by another layer, the risks should be reduced significantly.
Roofing and siding containing asbestos--such as Johns Mansville siding--pose a hazard because general wear and tear can leave asbestos particles in the soil around the home.