Asbestos is the name of a group of minerals with long, thin fibers. It was once used widely as insulation. It also occurs in the environment. Asbestos fibers are so small you can't see them. Disturbing asbestos can cause fibers to float in the air. When this happens, they are easy to inhale. You breathe out most fibers, but some become lodged in the lungs. Over time, they can build up in the lungs, causing scarring and inflammation.