The respiratory system refers to our lungs, with diseases and illnesses of the respiratory system greatly impacting our ability to breathe properly which can be life-threatening in some cases. The 5 common respiratory system diseases are:   ● Asthma is one of the most common respiratory diseases that affect people of all ages with no exact known cause. Inflammation in the airways makes it difficult to breathe, in some cases as the result of exposure to an allergen that triggers an allergic reaction. ● Chronic Obstructive Pulmonary Disease, or COPD, is a chronic respiratory disorder caused by long-term exposure to substances that damage your lungs such as cigarette smoke or air pollutants. ● Lung cancer is most commonly associated with cigarette smoke, but can also be caused by air pollution, asbestos or radon exposure, and second-hand smoke. ● Pneumonia is often the result of a cold or the flu but can also be caused by certain bacteria in the lungs that cause a lung infection that can range from mild to severe. ● Influenza, which is also known as the seasonal flu, passes from one person to another through the air due to its highly contagious nature.