Pleurisy (PLUR-ih-se) is a condition in which the pleura is inflamed. The pleura is a membrane that consists of two large, thin layers of tissue. One layer wraps around the outside of your lungs. The other layer lines the inside of your chest cavity.
Between the layers of tissue is a very thin space called the pleural space. Normally this space is filled with a small amount of fluid—about 4 teaspoons full. The fluid helps the two layers of the pleura glide smoothly past each other as you breathe in and out.
Pleurisy occurs if the two layers of the pleura become irritated and inflamed. Instead of gliding smoothly past each other, they rub together every time you breathe in. The rubbing can cause sharp pain.
Many conditions can cause pleurisy, including viral infections.