Nicotine and Associated Chemicals
         Tobacco is available in several forms: cigarettes, cigars, snuff, pipe, and chewing tobacco (also called "smokeless tobacco"). All of these contain the chemical stimulant nicotine.
          In its natural form, nicotine is a colorless liquid that turns brown upon oxidation (combining with oxygen). The oxidation that occurs during the burning of tobacco leaves releases the chemical from the leaves so that it can be inhaled into the body. Snuff is a powdered form of tobacco that is inhaled and absorbed through the mucous membranes in the nose. Chewing tobacco is placed between the gum and cheek and then sucked or chewed to release the nicotine. Chewing tobacco is usually not swallowed. The user must spit out the wad of chewed leaves after the nicotine has been released into the saliva.
         Nicotine is a powerful central nervous system stimulant that produces a variety of effects. The chemical's stimulant action on the cerebral cortex produces an aroused, alert mental state. Nicotine also stimulates the adrenal glands, resulting in the increased production of adrenaline. Physical effects of nicotine stimulation include increased heart rate and respiration, constriction of blood vessels, and increased blood pressure. This increased blood pressure (hypertension) is a direct result of constricted blood vessels. The heart must work harder to pump blood through the narrowed vessels. Habitual nicotine use can inflict serious damage on the heart and circulatory system.
         Nicotine use decreases the contractions of the stomach that signal hunger and elevate blood sugar levels. These factors, along with decreased sensation in the taste buds, reduce the appetite. 
         Beginning smokers often readily feel the effects of nicotine. These symptoms, which are called nicotine poisoning, include dizziness, lightheadedness, rapid erratic pulse, clammy skin, nausea, vomiting, and diarrhea. These effects cease as soon as tolerance to the drug develops. Some medical research indicates that tolerance to nicotine develops almost immediately in new users, as opposed to alcohol, where tolerance develops over a long period of time.

Cigars, Cigarettes and Pipes 
         Smoking is the most common form of tobacco use. Smoking delivers a strong dose of nicotine to the user, along with an additional 1,200 chemical substances. Among those other substances are various gases and vapors that carry particulate matter in concentrations as great as 5 billion parts per cubic millimeter. In contrast, the most air-polluted cities in the world have demonstrated a particulate matter concentration of only 10,000 parts per cubic millimeter. 
         Particulate matter condenses in the lungs to form a thick, brownish sludge called tar. Tars contain various carcinogenic (cancer-causing) agents like benzopyrene and other irritants such as the chemical phenol. Phenol and several other irritants have the potential to combine with other tobacco chemicals and contribute to the development of lung cancer. 
         Tars compose approximately 8 percent of the contents of tobacco smoke. The remaining 92 percent includes various gases, the most dangerous of which is carbon monoxide. In tobacco smoke, the concentrations of carbon monoxide are 400 times higher than the level considered safe by the Environmental Protection Agency. In the human body, carbon monoxide reduces the capacity of the blood to carry oxygen by binding with the receptor sites for oxygen. For some reason, carbon monoxide more readily attaches to these sites than does oxygen. Thus, smoking not only increases heart rate and blood pressure, but also hampers the capacity of the circulatory system to carry oxygen, causing deprivation in the body tissues. 
         The heat from smoked tobacco products can also be harmful. Inhaling hot gases and vapors exposes sensitive mucous membranes to irritants that can weaken the tissues and contribute to the development of oral, laryngeal, and throat cancers. 
         Tobacco manufacturers have responded to consumer worries about the relationship between smoking and cancer by producing cigarettes low in tar and nicotine and by placing filters on the ends of cigarettes. Although the use of these products does reduce cancer risks somewhat, the frequent user still faces greater health risks than the infrequent user or nonsmoker. Using low-tar, low-nicotine, or filtered products does no good at all if you use them as an excuse to smoke more cigarettes.
         The smoker choosing  low-tar and filtered cigarettes may be decreasing the risks of developing lung cancer while at the same time increasing the risks of developing heart and circulatory disorders. In many case, the low-tar and filtered cigarettes increase the level of carbon monoxide in the blood.
         Smokers can take other steps to protect themselves from cancer. Smoking only one half the cigarettes can reduce cancer risks by as much as 40 percent. Fewer drags as well as short, shallow drags will also reduce tar and nicotine dosages. Cutting down on the number of cigarettes smoked per day will also help reduce risks somewhat, but quitting the habit is the best method of risk reduction.

Secondhand Smoke 
         As the population of nonsmokers rises, so does the demand for the right to breathe clean air. Although smokers are a minority in this country 30 percent versus 70 percent nonsmokers-air pollution from smoking in public places continues to be a problem. 
         Groups such as GASP (Group Against Smokers' Pollution) and ASH (Action on Smoking and Health) have been working for more than a decade to reduce smoking in public places. Most states now have laws governing the use of cigarettes in public places such as restaurants, theaters, bowling alleys, public schools, airports, and bus depots. 
         Cigarette, cigar, and pipe smoke in enclosed areas presents hazards to nonsmokers. An estimated 10 to 15 percent of the nonsmoking population is allergic to cigarette smoke. These people experience painful headaches, nausea, and dizziness in response to minute amounts of smoke. The level of carbon monoxide in cigarette smoke in enclosed places is 4,000 times higher than those recommended by the Environmental Protection Agency for maximum clean air standards. 
         Lung cancer deaths among nonsmokers who breathe secondhand smoke are higher than among those who do not breathe secondhand smoke. Passive smokers are three times more likely to die of lung cancer than nonsmokers who do not breathe cigarette smoke.
         Family members may also be considered "involuntary" smokers each time someone in their household "lights up." Children whose parents smoke show a higher incidence of upper respiratory infections than do children of nonsmokers. Pregnant women who smoke increase their chances of having a miscarriage, producing a low-birth weight baby, or having a stillborn child. New research shows a possible link between smoking during pregnancy and sudden infant death syndrome (SIDS), or "crib death," a condition in which an infant, usually under 1 year of age, dies during its sleep for no apparent reason.
         The pregnant woman who shares space with smokers may also be endangering her unborn child. Although research on the hazardous effects of secondhand smoke on the unborn is not yet conclusive, many physicians advise their pregnant patients to avoid breathing second hand, or side stream, smoke.