[Toxicology of tobacco]

Tobacco is one of the major toxic agents in our civilization. The extent and severity of the current smoking epidemics are due to the use of industrial cigarettes: their smoke, less irritant than that of cigars and pipe, can be inhaled intensively with rapid absorption of all toxic compounds. Tobacco smoke is composed of a gas phase (CO2, CO, CNH, etc.) and a particle phase (a very fine aerosol) in which more than 4000 substances have been identified. The main toxic compounds in tobacco are Co, nicotine and tars. CO binds to haemoglobin to form COHb, a major factor of hypoxia and vascular accidents. Within a few seconds, nicotine reaches the brain where it binds to specific receptors, which explains its psycho-active effects (psychological dependence) and the induction of physical dependence. This dual dependence is responsible for the failures and relapses observed in attempted withdrawals. Furthermore, nicotine stimulates the sympathetic system with hypersecretion of catecholamines resulting in vascular complications. Tars contain carcinogenic substances, such as aromatic hydrocarbons, which exert local effects on the respiratory tract and systemic effects since they are absorbed by the lungs; this explains the remote neoplasias such as cancer of the bladder. Tars also contain irritant agents (acrolein, formaldehyde, etc.) and oxidative substances responsible for chronic bronchitis and emphysema. Thus, all organs and tissues can be damaged by the toxic compounds that are present in tobacco and, in particular, in tobacco smoke.