Chronic obstructive lung (or pulmonary) disease (COPD) is a disease of the air sacs and air passages of the lungs. People with COPD are short of breath and sometimes cough and wheeze. Chronic obstructive lung disease is usually caused by smoking; damage to the lungs and symptoms slowly worsen over time. Most patients also have intermittent bouts of acute worsening of symptoms. Lung infections, cold weather, and exertion may cause these bouts.