The term tar is sometimes mistaken to be a specific harmful chemical in cigarette smoke while cigarette tar refers to the total weight of solid and liquid residue in cigarette smoke after the weight of water and nicotine has been subtracted and is reported as a weight measurement. As such, cigarette tar is quantified after a cigarette is burned and, because of the combustion process, it includes harmful chemicals and carbon-based solid particles, the primary cause of smoking-related diseases. We review here the meaning of tar, aim to clarify any misconceptions surrounding it, and explain why this measurement can be misleading in assessing risk of different tobacco or nicotine-containing products.
Tar is the name for a specific fraction of cigarette smoke. Cigarette smoke is a complex mixture of chemicals including volatile compounds contained in the gas-vapor phase of the smoke and suspended liquid and solid particles. These liquid and solid particles are referred to as total particulate matter (TPM).
Tar refers to the total weight of TPM in cigarette smoke after the weight of water and nicotine has been subtracted:
Thus, cigarettes do not contain tar, exactly; rather, tar is calculated based on a measurement of cigarette smoke. It was originally introduced by the tobacco industry as a means of quality control for cigarettes, to ensure consistency in the mass of smoke delivered by each cigarette.
Cigarette tar is different from the tar used in road surfacing (which is a liquid substance composed of hydrocarbons). To avoid confusion between both terms, tar used in reference to cigarettes is sometimes put in quotation marks. The International Organization for Standardization (ISO), which has published the standard procedure for measuring tar in cigarette smoke under ISO 4837:2019, favors the term nicotine-free dry particulate matter (NFDPM) over tar.
To measure tar in cigarettes according to ISO 4837:2019, cigarette smoke is directed through a white filter pad (specifically, a Cambridge glass-fiber pad), which captures the TPM. By weighing the mass of the filter pad before and after TPM collection, the value of TPM can be found. The weight of the water and nicotine content are then measured and subtracted from the total TPM value. The value obtained from the subtraction of water and nicotine represents the tar in a cigarette and is reported as a weight.
The tar measured in cigarettes can vary significantly depending on the brand and type. As a general guideline, different cigarettes may yield from 7 mg of tar per cigarette to 22 mg per cigarette or even above.
In some countries, cigarette packages display information about the tar content (in mg). As such, tar has long been portrayed as an indicator of the detrimental health effects associated with smoking. However, tar is simply reported as a weight measurement, which does not provide any insight into its chemical composition. For this reason, the idea that tar could be helpful in evaluating the risks of smoking warrants closer scrutiny.
If we only take weight into account, tar measurement is not useful. The tar could contain a high proportion of highly toxic chemicals and a low proportion of less toxic ones—or just the opposite. There is no way of knowing because the weight measurement is quantitative and not qualitative in nature. Therefore, this measurement gives no indication of the risk of harm because the levels of toxicants within the tar are unknown.
When comparing tobacco products, whether they are cigarettes or smoke-free alternatives, it is more important to analyze the levels of individual toxicants emitted. When we look at the content of cigarette smoke, more than 6,000 chemicals have been detected, and within this complex mixture, about 100 have been identified as harmful or potentially harmful chemicals by public health authorities such as the U.S. Food and Drug Administration.
The short answer is yes, cigarette tar is harmful due to the harmful substances it contains, which originate from the cigarette smoke it is derived from. However, there is a public health and scientific consensus that the weight of the tar is not an accurate or precise indicator of risk or harm, and that reporting of tar measurements can be misleading to consumers. A clearer indicator of risk is knowing which chemicals the smoke contains and at what levels. This is why many governments and public health organizations have supported removing tar measurements from cigarette packaging.
For example, the European Union’s 2014 Tobacco Product Directive clarified that tar ratings are not the appropriate metric to identify a cigarette’s level of harm: “The indication of the emission levels for tar, nicotine and carbon monoxide on unit packets of cigarettes has proven to be misleading as it leads consumers to believe that certain cigarettes are less harmful than others.”
Heated tobacco products (HTPs) are designed to heat the tobacco just enough to release a nicotine-containing tobacco aerosol but without burning the tobacco. Because tobacco is heated and not burned there is no smoke, and in the case of our HTPs, we have demonstrated that the levels of harmful chemicals in the generated aerosols are significantly reduced compared with cigarette smoke. HTPs, though, are not risk free, and they provide nicotine, which is addictive.
The picture shows the visual difference between the particulate matter of standard reference cigarette smoke (1R6F, left) and the particulate matter of Tobacco Heating System (THS) aerosol (right) after collection on laboratory filter pads (1 stick per product, aerosol regime ISO 20778:2018).
Therefore, when comparing tobacco products, we need to look closely at the composition of the residue they generate instead of relying on weight. HTPs generate an aerosol residue that significantly differs in composition from the smoke residue produced by traditional cigarettes. Comparing the levels of harmful chemicals in HTP aerosols and cigarette smoke is a better indicator of risk.
