Asbestosis is a process of lung tissue scarring that is caused by asbestos fibers. Because many other diseases also lead to lung scarring, these other causes must be excluded first when a patient is found to have lung scarring. Patients with particular x-ray findings or biopsy results must also have a remote history of asbestos exposure and a characteristically delayed development of the condition in considering asbestosis as a diagnosis. Smoking appears to increase the frequency and/or the rate of progression of asbestosis, possibly by preventing the efficient elimination of inhaled fibers from the airways.