Pleural Thickening is a condition that causes fibrosis (excess connective tissue or “scarring”) of the outer lining (pleura) of the lung. The damage that is caused by the fibrosis causes thickening of the lining. Pleural thickening can restrict the function of the lung causing breathlessness and consequent disability. It is uncommon for the condition to be progressive in nature but it can cause a reduction in life expectancy. If a diagnosis of pleural thickening is to be made a history of asbestos exposure is required as the condition can be caused by other factors.