When tobacco is burned, it releases more than four thousand different chemicals. Two hundred of these chemicals are harmful to human health, and forty-three of them are carcinogenic. It is a common, though incorrect, belief that as long as the tobacco smoke is not inhaled into the lungs, then it could not cause any damage. When tobacco is burned, some of the chemicals are absorbed by the mucous membrane of the oral cavity, some are released into the surrounding air, and some will still make their way into the pulmonary system.

　　Tobacco contains four major types of chemicals:

　　Of these four types of chemicals, nicotine can cause central nervous system stimulation and eliminate sleepiness. This is the major reason why smoking cigarette is so addictive. In addition, nicotine can cause an increase in the heart rate and blood pressure, as well as constricting the peripheral blood vessels. A long history of cigarette smoking can increase the likelihood of having cardiac and arterial diseases, making it a major culprit of human morbidity.

　　Besides nicotine, the other three chemicals can cause major problems for our health. When carbon monoxide enters the human body, it will gradually hinder the ability of hemoglobin to bind to oxygen, resulting in low oxygen concentration in the blood, which could cause various heart ailments. The tar and stimulants are the major perpetrators for chronic obstructive pulmonary disease (COPD), including chronic bronchitis and emphysema. Besides lung cancer, cigarette smoking is also closely related to renal cancer, bladder cancer, esophageal cancer, and cervical cancer.

　　One of the most worrisome aspects of cigarette smoking is that, other chemicals in tobacco can interact with nicotine to make cigarette smoking even more addictive. It is particularly dangerous for the adolescents, because these chemicals can affect their mood, behavior, and thought process. Many young Attention Deficit Hyperactivity Disorder (ADHD) sufferers would rely on cigarette smoking for self-medication.