12.6 Additives and flavourings in tobacco products

Many of the flavouring additives are non-toxic, but they turn into toxic substances after being modified during burning. For instance, heated sugars produce pyrolysis products that are known toxicants and/or carcinogens.¹⁵

Liqueur/confectionery cigarettes are produced by diffusing volatile flavour essences throughout the cigarette or by a flavour pellet embedded in the filter.³⁶ As smoke is drawn through the filter, the casing of the pellet dissolves and the flavour essences are vaporised into the smoke.³⁶ Development of soluble pellet technology may explain the sudden appearance of liqueur/confectionery brands around the world in the early 2000s. Liqueur/confectionery flavour additives are believed to be part of ‘youth-oriented’ products (see Section 5.13), and likely to facilitate initiation among youth by masking the harshness of tobacco smoke in comparison with a 'full-flavour' cigarette.³⁷ The promotion and sale of fruit and confectionary flavoured cigarettes is now prohibited in all states and territories in Australia, see 10.8.4 for more details about flavoured cigarettes and tobacco in Australia.

Kreteks are cigarettes that originated in Indonesia, containing tobacco plus a significant amount of cloves (sun-dried flower buds of the clove tree). Kreteks also contain a ‘sauce’ that contributes to flavouring, with up to 100 ingredients.³⁸ Information on the sauce ingredients is scarce, but it may include chemicals that give a chocolate, strawberry, liquorice and/or banana taste.³⁹ Saccharin is added to the kretek wrapper to produce a sweet flavour.³⁸ Eugenol (clove oil) is found in kreteks at up to 7% of the weight of the filler. Other chemicals from the cloves include eugenol acetate, caryophyllene, α-humulene, and methyl eugenol.¹¹ The extent to which these contribute to the flavour of kreteks is poorly understood.

Bidis are hand-rolled, unfiltered cigarettes made in India and exported worldwide. They contain finely ground, sun dried tobacco rolled in a Tendu leaf (from the Tendu tree, native to India). Bidis are often high in added flavours, such as cherry, menthol, cinnamon, strawberry, vanilla, and raspberry.¹²

The tobacco used in waterpipes is usually highly flavoured and these flavours are a significant motivator for their use.^40-42 Fruity flavours are common. Benzyl alcohol, limonene, linalool and eugenol (clove oil) have also been detected in waterpipe tobacco.⁴³  

12.6.3.2 Reducing harshness and increasing smoothness

Reducing the harshness or increasing the smoothness of a product can improve the smoking experience, making it harder to quit and making young people more likely to take up smoking.^{1 ,33}  

Harshness has been carefully defined and measured by the tobacco industry; it is ‘a chemically induced physical effect associated with a roughness, rawness experience generally localised in the mouth and to a lesser degree in the upper reaches of the throat and the trachea due to inhalation of tobacco smoke.’¹ Nicotine, which is present in tobacco in substantial amounts, is one chemical that is responsible for the harshness of smoke.⁴⁴ Lowering the amount of nicotine, particularly the ratio of nicotine to tar, can reduce the harshness of smoke. Propylene glycol has been found to reduce the delivery of nicotine whilst increasing tar levels, and may reduce harshness.^{1 ,45} Added sugars, such as sucrose, glucose and fructose increase the acids in smoke, potentially lowering the available nicotine (‘free nicotine’, see Section 12.4.3.1), thereby reducing the harshness of the smoke on the mouth and throat.^{1 ,15 ,46}

An alternative approach is to increase the smoothness of smoke using additives that mask the harshness, without reducing delivery of nicotine. Chemicals that mask the harshness of smoke may do this by reducing the feeling of irritation felt in the mouth or throat when smoking.¹ Menthol and thymol are such additives, due to their local anaesthetic effect, see Section 12.7.2. Levulinic acid and levulinates are additives that can mask the harshness of smoke whilst maintaining or increasing nicotine delivery.^{1 ,47} Glycyrrhizin (found in liquorice) and other additives that make the taste sweeter can also mask the harshness of smoke.^{1 ,48} Eugenol (clove oil), which comprises up to 7% of the weight of kreteks, has local anaesthetic properties and may act to increase smoothness of these Indonesian cigarettes.⁴⁹

Humectants are chemicals that promote the retention of moisture in the tobacco (increase the humidity). Tobacco that becomes too dry has a harsh taste and feel, which can be improved with the addition of humectants.³³ Humectants commonly added to tobacco products include glycerol, propylene glycol and sorbitol.¹ By quantity per cigarette, humectants are one of the most common additives.

12.6.3.3 Improving the look and aroma of smoke

Many flavourings additives and added sugars produce appealing aromas when smoked. Improving the smell and appeal of the smoke may reduce the annoyance of the smoke to other people and therefore may improve the user experience of smoking.¹ Acetylpyrazine, anethole and limonene are additives that reduce the smell of sidestream smoke. Chemicals added to the wrapper, including magnesium oxide, magnesium carbonate, sodium acetate, sodium citrate and calcium carbonate can reduce the visibility of smoke.⁵⁰

12.6.3.4 Improving the look of tobacco products

Colouring agents such as pigments are added to tobacco products to modify their appearance.

Any colouring or other chemicals added to the cigarette paper forms part of the smoke that is inhaled as mainstream or sidestream smoke. These include chemicals that modify the burn rate, discussed in Section 12.6.4. Chemicals added to the filter may be inhaled, but those added to the tipping paper (around the filter) would not be.

In some countries, pigments are added to the cigarette paper or tipping paper to make cigarettes of varying colours,⁴⁹ which can make them more appealing, particularly to younger users.⁵¹ Pigments are also used to print branding on the cigarette paper and tipping paper. Titanium dioxide is often added to the cigarette filter as a whitening agent.⁵²

12.6.3.5 Creating the impression of health benefits

Additives in tobacco products have been used in some countries to create the impression, through brand naming, that these products have health benefits or reduced health hazards. Examples of these additives are vitamin C, vitamin E, fruit and vegetables extracts, amino acids such as cysteine and tryptophan, essential fatty acids such as omega-3 and omega-6,^{49 ,53} and charcoal in filters.⁵⁴

12.6.4 Additives that modify the processing, shelf-life and burn rates of tobacco products

Processing aids facilitate the manufacture of tobacco products, such as by making cured tobacco less brittle. These include several ammonium compounds, carbon dioxide and ethyl alcohol. Ammonium compounds make reconstituted tobacco sheets more pliable.⁵⁵

Combustion aids are used to control the smoking mechanics of cigarettes, such as by controlling the burning properties of cigarette paper. These can affect the rate at which burning occurs, and therefore the temperature. They include ammonium phosphate, sodium phosphate, sodium citrate and potassium citrate, which help to keep the cigarette lit.^{1 ,34 ,49}

Fillers are chemically inert substances that are used to increase the bulk of the tobacco rod. Calcium carbonate is an example of a filler.^{49 ,50}

Binders are used in reconstituted tobacco (made from stems and left over pieces of the tobacco plant) to make a paper-like material, that can be processed like normal tobacco lamina.⁵⁶ Cellulose fibre, guar gum and phenylacetaldehyde may be used as binders.⁴⁹

Preservatives increase the shelf-life of tobacco products. Benzoic acid and potassium sorbate are examples of preservatives in cigarettes.⁴⁹

Anti-microbials may include chemicals that prevent the growth of bacteria, fungi (such as mildew), parasites and other microbes in tobacco during processing or storage. As an organic product, tobacco is susceptible to infestation with these microbes after harvesting, particularly bacteria and fungi.⁵⁷ Menthol has some antibacterial and antifungal properties.⁵⁸ Eucalyptol is an additive that may have antimicrobial properties.⁴⁹ Note that fungicides used during the growing of tobacco may contaminate tobacco after harvesting and storage (but are not considered additives as such).

12.6.5 Toxicity of tobacco product additives

Some tobacco products additives are toxic, whilst others produce toxic products during combustion and pyrolysis when the tobacco is burned, see Section 12.4.2.1 and 12.4.2.2. Table 12.6.1 lists many tobacco additives that are toxic, or suspected to be toxic, in their unburned state (labelled TUB), or that produce toxic products after burning (labelled TAB). Titanium dioxide, diacetyl and guaiacol are examples of additives with known or suspected toxic activity in their unburned state. Three examples of chemicals with toxicity after burning are 1) sorbitol, which forms acetaldehyde and formaldehyde after pyrolysis, 2) glycerol, which forms acrolein, and 3) b-damascone, which forms benzene, toluene, anthracene and phenanthrene.³⁴ The toxicity and carcinogenicity (cancer-causing activity) of chemicals such as formaldehyde, acrolein and benzene are discussed in detail in Section 12.4.3.

Many tobacco additives, particularly flavourings, are regarded as safe for consumption in food. The US Food and Drug Administration (FDA) designates food additives as GRAS: Generally Recognized As Safe, after assessment by experts.⁵⁹ Tobacco additives such as guar gum, liquorice and diacetyl are designated GRAS.⁶⁰ However, these three additives, as well as others that are designated GRAS, are considered potentially toxic additives in tobacco. This discrepancy comes about because food additives are not burned or inhaled into the lungs. It is during burning that many of the toxic chemicals in tobacco emissions are created. Chemicals that are eaten in foods are processed by the gastrointestinal system, including exposure to acid in the stomach. Select nutrients are taken up into the blood stream from the gut, after being processed by enzymes. However, in the lungs, chemicals from the smoke quickly enter the blood stream without the same processing that occurs in the gut. That a chemical is designated GRAS by the FDA for food consumption certainly does not mean that it is safe to breathe in the emissions of this chemical that are created in a burning cigarette.³⁴

Many of the additives with known toxicity are also naturally present in tobacco product emissions. Examples are aldehydes produced by sugars when burned, as well as diacetyl (naturally present in tobacco plants) and ammonia in smoke, which are made from compounds naturally present in tobacco as well as added during processing.^{15 ,34} However, establishing whether these additives increase the harm to health from smoking is complex.

Toxicity of a chemical, such as a tobacco product additive, can be measured in a variety of ways, such as using cells grown in a laboratory, skin tests and other toxicity tests using rodents. Smoke inhalation experiments in rodents aim to emulate the exposure in humans.⁶¹ There is a lack of high-quality experimental data from testing of the toxicity of individual additives in cigarettes and other tobacco products. The reasons why these experiments are challenging are detailed in a 2017 review.⁶² Given that tobacco smoke is already a highly toxic mix of thousands of chemicals, and individual additives are often at low concentrations, any additional toxicity from an additive will likely be small in magnitude and difficult to detect. Very large numbers of samples or animals will be necessary to detect differences. Both unburned and burned products need to be tested, but the burned products of complex mixes such as natural extracts are mostly uncharacterised, making testing them difficult in animal experiments. Furthermore, many diseases caused by smoking, such as cancer, take a considerable length of time to become apparent, so short-term testing, such as rodent toxicity tests, are insufficient to examine the risks of these diseases. Such tests in animals for the chronic effects of toxicity are expensive, time-consuming and technically challenging. In addition, inhalation tests of individual additives would ideally require the use of tobacco products made with and without that additive, but that were otherwise identical—a task that is very difficult for independent researchers. The authors comment that ‘tobacco smoke is highly detrimental to health irrespective of whether burned tobacco contains additives or not. It is hard to justify killing a large number of animals merely to demonstrate that tobacco additives enhance, do not change or slightly attenuate the inherent toxicity of smoking.’⁶²

Regardless of the lack of direct evidence that a specific additive leads to health effects, it is well-established that additives such as menthol and flavours increase the uptake of smoking and make it harder to quit–thereby increasing the exposure of people to the multitude of toxic chemicals in tobacco smoke that are the cause of countless diseases and millions of deaths.^{1 ,62}

12.6.6 Priority additives for reporting in Europe

The European Commission mandated the independent Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) to produce a priority list of tobacco additives in cigarettes and roll-your-own tobacco. SCENIHR assessed the role of tobacco additives in the addictiveness, attractiveness and toxicity of tobacco products, publishing their scientific rationale in 2010,¹ and assessment of a range of additives for inclusion on a priority list in 2016.³⁴ SCENIHR identified and assessed 48 individual additives, listed in Table 12.6.1, for potential inclusion on a priority list, based on four inclusion criteria:^{34 ,63}

A. Contributing to the toxicity or addictiveness of the products concerned/increasing the toxicity or addictiveness of any of the products concerned to a significant or measurable degree;

B. Resulting in a characterising flavour;

C. Facilitating inhalation or nicotine uptake;

D. Leading to the formation of substances that have CMR (carcinogenic, mutagenic or reproductive toxicant) properties/increasing the CMR properties in any of the products concerned (cigarettes/roll-your-own) to a significant or measurable degree.

A final priority list of 15 additives (Table 12.6.1, column 3) was determined on the basis of those additives in the group of 48 that were highest priorities and most commonly used among cigarettes and roll-your-own products.^{34 ,35 ,63} Member States of the European Union require manufacturers and importers of cigarettes and roll-your-own products to carry out comprehensive studies on the additives on this priority list.³⁵

12.6.7 Additives in Australian cigarettes

Since the year 2000 there has been a voluntary agreement between the Commonwealth and the tobacco manufacturers for the disclosure of the ingredients in Australian cigarettes.⁶⁴ There are composite disclosures of hundreds of ingredients that companies say they potentially use. There are also brand-by-brand disclosures that list the major ingredients in descending order by weight. However, the industry claims that it cannot disclose all of the additives used in particular brands because that would mean giving up trade secrets and losing competitive advantage. Thus, it is not possible for consumers to know all of the ingredients used in each brand or the levels at which they are added.

Table 12.6.2 lists the additives in Australian cigarettes that were voluntarily disclosed to the Australian Government in 2020 by BAT Australia, Philip Morris and Imperial, the three main companies supplying cigarettes in Australia. The tobacco companies refer to these as ‘ingredients’. These include additives in the tobacco filler (flavours, binders, casings and humectants) as well as other parts of the cigarette, such as the filter, paper wrap, adhesives and inks. See Sections 12.8.1 and 12.8.2 for descriptions of these parts of cigarettes.

Most of the additives listed in Table 12.6.2 are burned and their burned products become part of the emissions that are inhaled by smokers and people near them. Exceptions are the filter, tipping paper and inks used on these components. However, unburned chemicals from these components may still be inhaled. As most of the toxic chemicals in smoke are produced by the burning process (see Section 12.4) the toxic chemicals produced from the burning of these additives are not in the list of additives.