Tar is the common name for the resin

Resin

Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

ous partially combusted and healed particulate matter produced by the burning of tobacco

Tobacco

Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...

 and other plant material in the act of smoking

Tobacco smoking

Tobacco smoking is the practice where tobacco is burned and the resulting smoke is inhaled. The practice may have begun as early as 5000–3000 BCE. Tobacco was introduced to Eurasia in the late 16th century where it followed common trade routes...

. Tar is purportedly the most destructive component in habitual tobacco smoking

Tobacco smoking

Tobacco smoking is the practice where tobacco is burned and the resulting smoke is inhaled. The practice may have begun as early as 5000–3000 BCE. Tobacco was introduced to Eurasia in the late 16th century where it followed common trade routes...

, 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 mutagen

Mutagen

In genetics, a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens...

ic and carcinogen

Carcinogen

A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...

ic agents in tobacco smoke (IARC, 1986). Polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...

s (PAH), for example, are genotoxic

Genotoxic

In genetics, genotoxicity describes a deleterious action on a cell's genetic material affecting its integrity. This includes both certain chemical compounds and certain types of radiation....

 via epoxidation.

There is a common misconception that the tar in cigarette

Cigarette

A cigarette is a small roll of finely cut tobacco leaves wrapped in a cylinder of thin paper for smoking. The cigarette is ignited at one end and allowed to smoulder; its smoke is inhaled from the other end, which is held in or to the mouth and in some cases a cigarette holder may be used as well...

s is equivalent to the tar

Asphalt concrete

Asphalt concrete is a composite material commonly used in construction projects such as road surfaces, airports and parking lots. It consists of asphalt and mineral aggregate mixed together, then laid down in layers and compacted...

 used on roads. As a result of this, cigarette companies in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, when prompted to give tar/nicotine

Nicotine

Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...

 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

Backronym

A backronym or bacronym is a phrase constructed purposely, such that an acronym can be formed to a specific desired word. Backronyms may be invented with serious or humorous intent, or may be a type of false or folk etymology....

 coined in the mid-1960s.

The European Union

European Union

The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 currently limits the tar yield of cigarettes to 10 mg.

Tar when in the lungs coats the cilia causing them to stop working and eventually die, causing such conditions as lung cancer

Lung cancer

Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...

 as the toxic particles in tobacco smoke are no longer trapped by the cilia but enter the alveoli directly.