CS is a complex mixture of more than 6,000 thousands of chemicals generated upon the burning or heating of tobacco leaves. These chemicals have cytotoxic, mutagenic, carcinogenic properties 1.
Each exposure to CS triggers an acute pattern of cellular responses which is superimposed onto the existing responses to any chronic CS exposure. Altogether these cellular/tissue responses are aimed at inactivating reactive CS constituents and adapting to the new microenvironmental conditions. If however the cell is overwhelmed by an attack of damaging principles that is not manageable by cellular defense mechanisms (including activation of apoptotic pathways), this results in unrepaired and therefore inheritable genotoxic damage (mutational lesions) or cell death by necrotic pathway. At the cellular levels many toxic effects induced by CS, particularly the induction of carcinogenesis, result from direct genetic or epigenetic effects causing altered gene functions (for example, cell cycle, DNA repair, and tumor suppressor genes).
These cellular responses are the cause of harmful sometimes even irreversible damages to the structure and function of tissues directly and not-directly exposed: periodontal tissues, respiratory tract, cardiovascular tissues, immune system, musculoskeletal system, digestive tract, sexual organs and skin.
Tissue injury of healthy smokers may precede the development of CS-associated diseases: cancer (lung, colon, cervix, liver, stomach, pancreas), COPD, stroke, impotence, heart disease, asthma, diabetes among others 2-4.