what causes lungs to produce too much thick mucus?
Photo Credit thorax x-ray of the lungs image by JoLin from <a href='http://www.fotolia.com'>Fotolia.com</a>. Mucus is a thick fluid secreted by mucus cells that are located in various organs. Mucus acts as a protective barrier and filter by coating the lining of organs to trap foreign substances. When foreign substances become trapped in the mucus, they cannot invade the body and cause sickness. A number of lung diseases can cause too much mucus to build up in the lungs. When mucus accumulates in the lungs, it can cause a mucus-filled cough and difficulty breathing.