When tar cools it forms a brown sticky mass on your lungs. It sticks to the Cilia, the tiny hairlike structures that line the airway in the lungs. They typically act as little brooms that sweep out harmful dirt but when cigarette smoke is inhaled, the Cilia can’t work properly because the tar sticks to it and covers it. With the Cilia not performing its task properly, dirt can stay in the lungs and causes more problems. Mucus gets piled up and germs don’t get out. Over time as smoking gets heavier and more frequent, the Cilia dies and the lungs are exposed to more dangerous substances. The mucus blocks the tiny airways in the lungs. The result is a need to cough to get rid of the mucus, that’s why smokers cough a lot. As the mucus increases, it thickens. This in turn leads to the lungs and airways getting irritated and they inflame, narrowing and reducing airflow.