Tobacco smoking

Tobacco smoking is the practice where tobacco is burned and the vapors either tasted or inhaled. The practice began as early as 5000–3000 BC.^[1] Many civilizations burnt incense during religious rituals, which was later adopted for pleasure or as a social tool.^[2] Tobacco was introduced to the old world in the late 1500s where it followed common trade routes. The substance was met with frequent criticism, but became popular nonetheless.^[3] German scientists formally identified the link between smoking and lung cancer in the late 1920s leading the first anti-smoking campaign in modern history. The movement, however, failed to reach across enemy lines during the Second World War, and quickly became unpopular thereafter.^[4] In 1950, health authorities again began to suggest a relationship between smoking and cancer.^[5] Scientific evidence mounted in the 1980s, which prompted political action against the practice. Rates of consumption from 1965 onward in the developed world have either peaked or declined.^[6] They however continue to climb in the developing world.^[7]

Smoking is the most common method of consuming tobacco, and tobacco is the most common substance smoked. The agricultural product is often mixed with other additives^[8] and then pyrolyzed. The resulting vapors are then inhaled and the active substances absorbed through the alveoli in the lungs.^[9] The active substances trigger chemical reactions in nerve endings which hightens heart rate, memory, alertness,^[10] and reaction time.^[11] Dopamine and later endorphins are released, which are often associated with reward and pleasure.^[12] As of 2000, smoking is practiced by some 1.22 billion people. Men are more likely to smoke than women,^[13] however the gender gap declines with younger age.^[14][15] The poor are more likely to smoke than the wealthy, and people of developing countries than those of developed countries.^[7]

Many smokers begin during adolescence or early adulthood. During the early stages, smoking provides pleasurable sensations and thus serves as a source of positive reinforcement. After an individual has smoked for many years, the avoidance of withdrawal symptoms and negative reinforcement become the key motivations.