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. If you disturb asbestos, the fibers can float in the air. This makes them easy to inhale, and some may become lodged in the lungs. If you breathe in high levels of asbestos over a long period of time, the fibers can build up in the lungs. This causes scarring and inflammation, and can affect breathing. Eventually it can lead to diseases such as: Asbestosis, or scarring of the lungs that makes it hard to breathe Mesothelioma, a rare cancer that affects the lining of the lungs or abdomen Lung cancer Lung diseases associated with asbestos usually develop over many years. People who become ill from asbestos are usually exposed on the job over long periods of time. Smoking cigarettes increases the risk. Agency for Toxic Substances and Disease Registry