Pictured is the respiratory tract, projected onto a body-silhouette.
Its direct connection to the bodies surroundings makes the respiratory system especially vulnerable to harmful influences, f.ex. many viruses or cigarette smoke.
All sections of the respiratory system can be affected by infections. The most common illnesses are the common cold, bronchitis and pneumonia.
Cigarette smoke contains poisonous and cancerous substances. Smoking increases the risk of contracting infections, COPD and different forms of cancer, of which the most common is lung cancer (of the brochi).