Asbestos is a mineral fiber that used to be added to a variety of products to strengthen them and provide heat insulation and fire resistance. It can only be identified with a special microscope in a professional lab setting. Most products made today do not contain asbestos, unless labeled. But older common products that might have contained asbestos in the past, and conditions which may release fibers, include: steam pipes, boilers, furnace ducts, floor tiles (vinyl, asphalt, rubber), adhesives, millboard & paper used as insulation around furnaces and wood-burning stoves, door gaskets & worn seals, soundproofing or decorative material sprayed on walls and ceilings, patching & joint compounds, textured paints, asbestos cement roofing, shingles and siding. Houses built between 1930 and 1950 may have asbestos as insulation.
If disturbed, asbestos material may release asbestos fibers, which can be inhaled into the lungs, and can lead to increased risk of lung cancers Mesothelioma and Asbestosis. It can take up to 20-30 years for symptoms to appear after first exposure. The fibers can remain there for a long time, increasing the risk of disease.
If you think asbestos may be in your home, usually the best thing is to leave asbestos material that is in good condition alone. Generally, material in good condition will not release asbestos fibers. Check material regularly if you suspect it may contain asbestos. Don't touch it, but look for signs of wear or damage such as tears, abrasions, or water damage. Check with local health, environmental, or other appropriate officials to find out proper handling and disposal procedures. If asbestos material is more than slightly damaged, or if you are going to make changes in your home that might disturb it, repair or removal by a professional is needed.
Repair typically involves sealing or covering asbestos material. Sealing involves treating the material with a sealant that either binds the asbestos fibers together or coats the material so fibers are not released. Covering involves placing something over or around the material that contains asbestos to prevent release of fibers. With any type of repair, the asbestos remains in place. Repair is usually cheaper than removal, but it may make later removal of asbestos, if necessary, more difficult and costly. All minor and major repairs must be done by a professional trained in methods for safely handling asbestos.
From the CPSC website: https://www.cpsc.gov/safety-education/safety-guides/home/asbestos-home