“acute viral infection, such as the flu (influenza), Bacterial or viral infections of the lungs (pneumonia
) where the infected portion of the lung involves the pleural surface, Autoimmune conditions such as lupus, rheumatoid arthritis and
autoimmune hepatitis, Tuberculosis and
other infections, A blood clot in an artery of your lungs (pulmonary embolism
), Pancreatitis, Cancer, Trauma (injury) to the chest or after heart surgery. Sometimes a cause cannot be found (ideopathic pleurisy).