Illustration of the respiratory tract projected onto a silhouette of a body. It shows the nasal and oral cavity, pharynx, trachea, both lungs and the heart between them. Due to its direct connection to the environment, the respiratory tract is particularly sensitive against harmful influences, especially viruses and tobacco smoke. All segments can be affected by an infection, the most common diseases are cold, bronchitis, and pneumonia. Smoking increases the risk of catching infections, COPD, and various types of cancer, especially lung cancer (bronchial carcinoma).