How can smoking contribute to cancer?

[Anandi]

Smoking cigarettes contribute to cancer and heart disease. Cigarette smoke contains tar which will stimulate the cells of the lungs to divide abnormally, causing lung cancer. Carbon dioxide in cigarette smoke combines more readily with heamoglobin that will reduce the oxygen carrying capacity of blood. It may strain the heart and cause heart disease.
Nicotine in cigarette smoke increases the heart rate and raises the blood pressure, thus increases the work load upon the heart to cause heart disease.

[Anandi]

Smoking not only endangers the health of the smoker but also the health of people (non-smokers) who are forced to inhale the air containing the smoke. Non-smokers are often forced to breath in the smoke produced by other people (smokers), particularly in enclosed situations. For this reason and because many people find the smell of cigarette smoke unpleasant, smoking is banned in many places and is regarded as a socially unacceptable behaviour.