A chemical substance made when tobacco is burned. Tar contains most of the cancer-causing and other harmful chemicals found in tobacco smoke. When tobacco smoke is inhaled, the tar can form a sticky layer on the inside of the lungs. This damages the lungs and may lead to lung cancer, emphysema, or other lung problems. Cigarettes and other smoked tobacco products may produce different amounts of tar, depending on how they are made. Inhaling tobacco smoke also causes other types of cancer, including cancers of the mouth and throat.