Tar is the common name for the resinous partially combusted and healed particulate matter produced by the burning of tobacco and other plant material in the act of smoking. Tar is purportedly the most destructive component in habitual tobacco smoking, accumulating in the smoker's lungs over time and damaging them through various biochemical and mechanical processes. Tar also damages the mouth by rotting and blackening teeth, damaging gums and blocking papillae and taste buds and the eye's vision.

Tar includes the majority of mutagenic and carcinogenic agents in tobacco smoke (IARC, 1986). Polycyclic aromatic hydrocarbons (PAH), for example, are genotoxic via epoxidation.