[Carcinogenic effect of tobacco smoke]

Both epidemiological and experimental studies provide evidence of the dose-effect relationship between the number of cigarettes smoked and lung cancer risk, exposure to tar or tobacco smoke and skin cancers or squamous cell carcinoma of the trachea and lung. Polycyclic aromatic hydrocarbons (PAHs) and volatile N-nitrosamines, and also tobacco specific N-nitrosamines are considered to be the major carcinogens in tobacco smoke. To exert carcinogenic effect these compounds require previous metabolic activation by biotransformation enzymes. Individual susceptibility to chemical carcinogens is genotype and phenotype dependent. Machine-measured yields of tar, nicotine, carbon monoxide, benzo[a]pyrene and N-nitrosonornicotine in cigarette smoke are significantly lower than actual intake by smokers. The following features have significant influence on the tobacco smoke composition, cancer risk and other disease risks relative to cigarette smoking: tobacco type and its modifications and also nitrate content in tobacco. Tobacco additives, including ammonia releasing substances, do not contribute to cigarette smoke composition and its toxicity. Filters, paper porosity, cigarette length and circumference as well as the number of tobacco cuts per inch (whether it is coarse-cut or fine-cut tobacco) are of primary significance for the chemical composition of cigarette smoke and health risk.