They are caused by asbestos fibers that invade the pleura from the lungs. Medical researchers do not fully understand the underlying processes of why asbestos fibers cause plaques to develop. Plaques rarely make breathing difficult and by themselves are seldom disabling. However, a person who has plaques should be vigilant about his or her health. He or she may be at higher risk for developing other asbestos-related diseases and should therefore advise his or her doctor about this asbestos exposure.
Pleural thickening is a diffuse fibrosis in the pleura.
Asbestos fibers that move from the lung to the pleura cause the pleura to thicken and a widespread fibrosis can develop. Researchers do not understand the underlying processes by which asbestos fibers cause fibrosis. This thickening can restrict the lungs' ability to expand and contract, and therefore make breathing difficult. Like plaques, thickening is evidence of exposure to asbestos and it places people at higher risk of developing other more serious chest diseases. Some effusions cause chest pains, but many do not cause any symptoms.