Pleurisy (also known as pleuritis) is an inflammation of the pleurae, the membranes of the pleural cavity surrounding the lungs. There are many possible causes of pleurisy but viral infections spreading from the lungs to the pleural cavity are the most common. The inflamed pleural layers rub against each other every time the lungs expand to breathe in air. This can cause sharp pain when breathing, also called pleuritic chest pain. The condition may either be primary or secondary and is often associated with a pleural effusion.