Cigarette smoke contains some 4,000 chemicals, several of which are known carcinogens. Perhaps the most dangerous substance in tobacco smoke is nicotine. Nicotine is the substance that reinforces and strengthens the desire to smoke. Because nicotine is highly addictive, addicts find it very difficult to stop smoking. Of 1,000 typical smokers, fewer than 20 percent succeed in stopping on the first try.
Many people smoke because they believe cigarettes calm their nerves.
Actually, smoking releases epinephrine, a hormone which creates physiological stress in the smoker, rather than relaxation. Tobacco is addictive. Most users develop a tolerance for nicotine and need greater amounts to produce a desired effect. Smokers become physically and psychologically dependent and will suffer withdrawal symptoms when use is stopped. Use your head .