Progressive lung disease is not fully reversible and clogs the airways, making breathing difficult. The blockage may improve only in part with drug therapy. Major risk factors: cigarette smoke, dust, chemicals and air pollution. Symptoms: shortness of breath, coughing, wheezing and shortness of breath even with modest strain. Many patients have a chronic cough which is particularly intense in the morning. With the progression of the disease, periods between exacerbations become shorter until the onset of hypoxemia with cyanosis.