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.

There is a common misconception that the tar in cigarettes is equivalent to the tar used on roads. As a result of this, cigarette companies in the United States, when prompted to give tar/nicotine ratings for cigarettes, usually use "tar", in quotation marks, to indicate that it is not the road surface component. Tar is occasionally referred to as an acronym for total aerosol residue, a backronym coined in the mid-1960s.

The European Union currently limits the tar yield of cigarettes to 10mg.

Source: Tar (tobacco residue) - Wikipedia, the free encyclopedia