Evaluating cancer risks: The impact of thirdhand smoke exposure on carcinogenesis.

The impact of firsthand and secondhand smoking on the development of various types of cancer is well established. However, the association of thirdhand smoke (THS) with malignant diseases has only recently been recognized, with limited research investigating the underlying mechanisms. THS refers to the dynamic mixture of residual tobacco smoke constituents that persist in air, dust, and on surfaces, and can occur through dermal absorption, inhalation of re-emitted gases and particles, and ingestion - particularly via dust intake. Tobacco smoke contains hundreds of toxic compounds, 60 of which are classified as carcinogens. These include aromatic amines, nicotine, nitrosamines, nitric oxide and polycyclic aromatic hydrocarbons. These substances can react with environmental chemicals, forming highly toxic secondary pollutants that can be released from surfaces over months and be absorbed through the skin or mucosa. The metabolization of tobacco smoke components can increase the incidence of cancer by altering key molecular pathways. Main mechanisms of carcinogenesis include DNA adduct formation and DNA structural changes, interference with tumor suppressor genes, and chronic inflammation. This review examines the risks of THS exposure, the potential mechanisms of carcinogenesis associated with THS and the role of THS in the development of different cancers linked to tobacco use.