With each puff of a cigarette, a smoker comes in contact with more than 4,000 chemicals, and at least 43 of these are known to cause cancer. But the chemicals in tobacco can cause other ailments as well. Tobacco contains nicotine, the addictive drug in cigarettes. People smoke to reduce the craving for nicotine, which is a poisonous stimulant. A stimulant is a drug that increases the action of the central nervous system, the heart, and other organs. Nicotine raises blood pressure and increases heart rate.

The flavor of a cigarette is due mostly to the tar in tobacco. Tar is a thick, sticky, dark fluid produced when tobacco burns. Several substances in tar are known carcinogens, cancer-causing substances. Tar penetrates the smoker's airways and lungs. Combined with the drying effect of cigarette smoke, tar paralyzes or destroys cilia, the waving hair like projections that work to keep the respiratory track clear.

Carbon monoxide is a colorless, poisonous gas in cigarette smoke that passes through the lungs into the blood. This is the same gas in automobile fumes that, if inhaled, could prove fatal. It united with the hemoglobin in red blood cells, preventing them from carrying the oxygen needed for energy to the body's cells.