Lung cancer is the most common form of cancer caused by smoking. More than 80% of cases of lung cancer are due to smoking.
Cigarette smoke contains many chemicals that interfere with the body's method of filtering air and cleaning out the lungs. The smoke irritates the lungs and leads to overproduction of mucus. It also paralyses the cilia - tiny hair-like structures that line the airways and clean out dust and dirt. Paralysis of the cilia means mucus and toxic substances accumulate, resulting in congestion of the lungs.
This extra mucus means smokers are more likely to suffer from chronic bronchitis and what is known as 'smoker's cough'.
Cigarette smoke is one of the best known triggers of asthma. When people suffer from asthma their inflamed air passages, which are very sensitive, narrow when exposed to cigarette smoke. This causes an asthma attack.
Long term exposure of the lungs to the irritants in tobacco smoke destroys the normal lung structure. The elastic walls of the small airways within the lungs are broken down. This reduces the amount of lung tissue available for the transfer of oxygen from the air to the blood. This condition is called emphysema. Some degree of emphysema is found in almost all people who are long-term smokers, however the severity will vary depending on the amount of cigarettes smoked, and the number of years the individual smokes.