Chronic obstructive pulmonary disease (COPD), also known as chronic obstructive lung disease (COLD), and chronic obstructive airway disease (COAD), is a collection of diseases which make breathing gradually more difficult.

Symptoms of COPD include difficulty breathing and cough, in particular coughing up lots of phlegm. It is usually caused by smoking cigarettes, and around half of people who smoke for their whole lives will develop COPD.Air pollution can be another cause, particularly in countries where indoor fires are used without ventilation.