18B.5 Exposure to chemicals from heated tobacco products

Last updated: May 2024        

Suggested citation:  Winnall, WR, & Kalitsis, L. 18B.5 Exposure to chemicals from heated tobacco products. In Greenhalgh EM, Scollo, MM and Winstanley, MH [editors]. Tobacco in Australia: Facts and issues. Melbourne: Cancer Council Victoria; 2024. Available from https://www.tobaccoinaustralia.org.au/chapter-18-e-cigarettes/indepth-18b-non-combustible-cigarettes/18b-5-exposure-to-chemicals-from-heated-tobacco-products

 

Heated tobacco products are devices that heat cigarette-like ‘sticks’ of tobacco to produce a smoky emission that is inhaled by users. They differ from e-cigarettes, in that they contain tobacco, and differ from conventional cigarettes as they heat this tobacco to a lower temperature. But their emissions contain many of the same chemicals in cigarette smoke, including toxic chemicals that are known causes of serious diseases. 

Heated tobacco products are a range of different device types and tobacco sticks with differing modes of use (see InDepth 18B.1). But these do not vary as much as the even wider range of e-cigarettes. Much of the available research has studied either the Philip Morris International (PMI) product IQOS or British American Tobacco’s (BAT) Glo.

Many of the studies of the chemicals in heated tobacco emission come from the tobacco industry. However, with the exception of biomarkers of exposure ( InDepth 18B.5.6), there is sufficient research from independent scientists to inform the chemicals present in these emissions without drawing on industry research. Herein, independent sources are cited, except where noted in the text.

18B.5.1 What are the emissions from heated tobacco products?

18B.5.1.1 Aerosols from heated tobacco products

Heated tobacco product emissions are an aerosol, consisting of a mix of particles and gases. The particles of an aerosol are tiny droplets of liquids or solids that float in the gases. The chemicals in these emissions are in the droplets, as well as the gases, which include carbon monoxide. Note that the emissions from e-cigarettes, tobacco cigarettes and other types of burned tobacco are also aerosols.

IQOS devices were shown to produce aerosol particles in a range of sizes, with the predominating size being under 2.5 μm in diameter (known as PM 2.5). In general, particles from smoke that are PM 2.5 are most likely to lodge deep in the lungs and most dangerous to health. 1 Particulate matter containing particles less than 10 μm in diameter (PM 10), PM 2.5 and PM 1 were all detected in the emissions of IQOS. 2 PM 2.5 was also detected in the emissions from IQOS, glo and Ploom devices. 3 A study published by PMI identified 529 chemicals present in the mainstream aerosol of IQOS, with the majority in the particulate phase. 4

18B.5.1.2 Mainstream emissions, sidestream emissions and secondhand emissions from heated tobacco products

As for conventional cigarettes, the mainstream emissions of heated tobacco products are those directly inhaled from the device by the user.

For conventional cigarettes, sidestream emissions come from the smouldering tip of the cigarette between puffs (see Section 12.4.1.2). IQOS heated tobacco products have been shown to produce sidestream emissions in research funded by Imperial Tobacco, who are competitors of the manufacturers of IQOS. In this study, IQOS products released numerous detectable chemicals after heating but not while being puffed by a user. 5

Secondhand emissions from heated tobacco products are discussed below in InDepth 18B.5.5.

18B.5.1.3 Do heated tobacco products produce smoke?

The smoke produced by cigarettes is formed by many different chemical reactions. These include combustion and pyrolysis reactions (see Section 12.4.2 for descriptions). Although the lower temperatures in heated tobacco products mean that combustion is unlikely to be happening, many of the other types of chemical reactions that make cigarette smoke are occurring during the generation of the smoky emissions from heated tobacco products. These emissions contain many of the same chemicals, including the toxic chemicals found in tobacco smoke. Given its strong similarity to tobacco smoke from cigarettes, calling heated tobacco product emissions ‘smoke-free’, as the tobacco industry does, is highly misleading.

Smoke from cigarettes

Tobacco smoke from cigarettes is complex mixture of thousands of chemicals that are either gases or contained within the particles of the aerosol. 6 Many of these chemicals are produced anew during the burning of the cigarette in chemical and physical reactions known as incomplete combustion, incomplete pyrolysis, pyrosynthesis, distillation and sublimation. See Section 12.4.2 for explanations of these terms. Some of the substances in cigarette smoke, such as cadmium and other toxic metals, are directly transferred from the tobacco into the smoke, rather than undergoing chemical reactions.

Smoky emissions from heated tobacco products

The emissions from heated tobacco products are an aerosol that contains hundreds, 4 and possibly thousands of chemicals. The lower temperature, differences in the tobacco, and additives in heated tobacco products mean that the range of chemicals in the emissions from conventional cigarettes and heated tobacco products differ. It’s unlikely that combustion (self-sustaining oxidative reactions) is occurring at these low temperatures. 7 However the production of carbon monoxide by heated tobacco products indicates that some oxidative chemical reactions are occurring. The emissions of heated tobacco products contain many of the same chemicals found in tobacco smoke, including harmful and potentially harmful chemicals (HPHC) identified by the US Food and Drug Administration (FDA) (see Table 18B.5.1). 8 , 9 Furthermore, the emissions from heated tobacco products produce tar, just like cigarettes do (see InDepth 18B.5.3.2 below). 10 , 11 Despite the many similarities between the aerosols produced by cigarettes and those produced by heated tobacco products, the tobacco industry claims that the aerosols from the latter are not smoke, and that these products are ‘smoke-free’. 12 The tobacco industry claims that if combustion is not occurring then the emissions are not defined as smoke.

Independent researchers have argued that IQOS emissions fit both the definition of aerosols and smoke. In one review, the authors argue that heated tobacco product emissions should be considered as smoke because: 1) much of the emissions are produced by endothermic pyrolytic reactions 13 at 320 to 350°C, which is similar to tobacco smoke that also contains many chemicals from these reactions, 2) relatively high tar yields are drawn from IQOS emissions, 3) there are reports of black carbon being present in the emission, consistent with some combustion occurring, and 4) definitions of smoke and aerosols used by CORESTA and the tobacco industry in previous scientific publications are quite varied and many have not insisted that combustion products are an essential component of tobacco smoke. 7 Another argument by independent researchers cites Principle 1 in Guidelines for implementing Article 8 of the World Health Organization’s Framework Convention on Tobacco Control (FCTC), which states:

’There is no safe level of exposure to tobacco smoke, and notions such as a threshold value for toxicity from second-hand smoke should be rejected, as they are contradicted by scientific evidence’. 14

These authors detected volatile organic compounds, polycyclic aromatic hydrocarbons, and carbon monoxide in the emissions from IQOS— the same harmful constituents of smoke from conventional cigarettes. The constituents of heated tobacco product emissions, as described in this section, show that they contain many of the harmful constituents of cigarette smoke; claims of being ‘smoke-free’ are therefore misleading.

One commentary provided an analogy with burning bread in a toaster. 15 If a toaster is set to approximately 200°C and the bread is cooked for long enough, then it will become black with char. A stinky smoke will be emitted that no-one would refer to as ‘bread vapour’. Under the Philip Morris definition of smoke, this emission would be referred to as ‘smoke-free’, which is highly misleading as this smoky emission contains many of the same toxic constituents of any smoke that is produced from burning organic material. 15

Another study reported carbon monoxide production and charring of the tobacco due to pyrolysis. They argued that charring, pyrolysis and the presence of carbon monoxide is evidence that the device burns the tobacco and produces smoke, as defined by the Oxford dictionary. 16

18B.5.2 Measuring the chemicals in heated tobacco product emissions

Heated tobacco devices, the tobacco sticks used in them and their modes of use vary considerably. These variations include different methods of heating the tobacco sticks (see InDepth 18B.1.2), varying puff times and volumes, and importantly, the temperature of the tobacco during use, which can affect the types of chemical reactions that occur during heating. 17 The current methods used in many studies to measure these emissions are not yet standardised. This means that comparisons across different laboratories and different types of tests are not necessarily valid.

The International Organization for Standardization (ISO) has created a working group for the development of protocols for testing heated tobacco products. 17 ISO has started to develop protocols. It has released one document with definitions and standard conditions for aerosol generation and collection from electronically heated tobacco products. 18 To date, other protocols are in development, such as for measuring carbon monoxide content.

Most of the methods used by researchers and tobacco industry employees to analyse the chemical contents of heated tobacco product emissions are adapted from protocols used to analyse conventional cigarettes or e-cigarettes. 13 , 19 A ‘smoking machine’ with one or multiple openings is used to ‘smoke’ the devices using suction. A filter pad is used to collect the particle phase of the aerosol and gases are separately collected for analysis. As for conventional cigarette emissions, tar yield is calculated from the weight of the residue on the filter pad minus the nicotine and estimated water content. Nicotine can be detected in the gaseous phase or the particle phase. More specialised methods such as mass spectrometry and gas chromatography are used to detected specific chemicals in the emissions (see Section 12.5.3 for explanations of these methods).

A lack of a reference material (i.e. a standard tobacco stick heated under set conditions) is currently problematic. 17 Emissions from differing products need to be compared to a heated tobacco reference in each individual experiment, in order to make comparisons across differing testing laboratories. Currently, researchers use conventional cigarette references such as 3R4F to compare to heated tobacco products in their experiments, partially addressing this problem.

Testing methods have also been established to analyse the contents of the tobacco sticks (prior to their use) made for heated tobacco products. 20 Measurement of the secondhand emission from heated tobacco products is discussed below in InDepth 18B.5.5.

Given the preliminary nature of emissions analyses and limitations discussed above, the WHO study group on tobacco product regulation has stated (in 2021) that ‘…generic statements of relative risk for users of these products are still preliminary and should be used carefully and cited only with recognition of this context.’ 17

18B.5.3 Chemicals in the emissions from heated tobacco products

18B.5.3.1 Nicotine

The emissions from heated tobacco products contain nicotine, the highly addictive component of tobacco. The tobacco sticks are usually smaller than conventional cigarettes, and they generally contain less total nicotine per stick. 17

A review of the literature in the 8th report of the WHO Study Group on Tobacco Product Regulation summarised the nicotine levels found in IQOS and glo emissions. 17 Among four different flavours of IQOS products the nicotine content in emissions ranged from 1.1 to 1.5 mg per stick and across six different glo products it ranged from 0.17 to 0.5 mg per stick. In these experiments, the reference cigarettes ranged from 1.0 to 2.73 mg of nicotine in emissions per cigarette. 17

In one study, the nicotine found in IQOS was all nicotine salts, as opposed to free-base nicotine. 21 Another study estimated between 5.7% to 13.6% of nicotine in emissions was free-base form. 22 See Section 18.5.3.1 for more information on nicotine salts.

In a study of 15 experienced users of heated tobacco products and conventional cigarettes, there was no difference in the total nicotine delivery to the blood, or nicotine delivery over time up to 90 minutes, between these products. 23

18B.5.3.2 Toxic substances

Heated tobacco products generally contain lower levels of harmful substances compared to conventional cigarettes, but higher levels than e-cigarettes. Chemicals detected in heated tobacco products are listed in Table 18B.5.1. See InDepth 18B.5.4 below for comparisons between product types.

Tar

Tar is defined as the total particulate matter of the aerosol, minus the water and nicotine. Heated tobacco products produce a considerable amount of tar, close to that produced by conventional cigarettes. Independent researchers have found 7.47 mg of tar per stick from IQOS compared to 7.98 mg per conventional cigarette when ISO standard puffing conditions (one 35ml puff each minute) were used. Under the more intensive puffing conditions (one 55ml puff each minute), IQOS produced 16.60 mg tar per stick compared to 25.50 mg per conventional cigarette. 10 Similar amounts were detected in other studies. 11  

Carbon monoxide

Carbon monoxide is a highly toxic gas found in tobacco smoke that contributes to heart disease and other health effects of smoking (see Section 12.4.3.9). It is designated as a harmful or potentially harmful constituent of tobacco by the FDA. 24 Carbon monoxide is produced by oxidative reactions such as combustion reactions.

Independent researchers have found carbon monoxide in the emissions of IQOS. 10 , 25 , 26 One study detected an average of 328 ppm (parts per million) compared to >2,000 ppm for conventional cigarettes. 26 A report from Public Health England found that heated tobacco users are exposed to between 23% and 47% the amount of carbon monoxide that cigarette smokers are exposed. 27

A tobacco industry paper studying the emissions from glo products detected carbon monoxide at low levels, at least 99% reduced compared to conventional cigarette references. 28 Carbon monoxide was not detected in the emissions from Ploom products as reported by the company that makes them. 29 These emissions come from an e-liquid that passes over tobacco, which undergoes considerably less heating than that in IQOS and glo.

Tobacco-specific nitrosamines (TSNA)

There are nine nitrosamines (compounds that can damage DNA and cause cancer) on the FDA’s list of harmful and potential harmful constituents of tobacco, 24 which includes those only found in tobacco (tobacco-specific nitrosamines (TSNAs)). TSNAs found in tobacco smoke are known causes of cancer. 30 See Section 12.4.3.7 for more information about nitrosamines in tobacco.

TSNAs are formed during tobacco curing and ageing rather than during combustion, and are therefore likely to be present in the tobacco sticks used in heated tobacco products. 31 Many studies from independent researchers have detected TSNAs in the emissions of heated tobacco products. 17 , 25 , 27 , 32 , 33 One study found four different TNSAs, including the toxic NNN ( N-Nitrosonornicotine) and NNK (4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone) in heated tobacco product emissions. 34 This study also showed that these chemicals were present in IQOS emissions at approximately one tenth the levels of those in Marlboro cigarettes per puff. 34

Polycyclic aromatic hydrocarbons (PAH)

There are approximately 60 types of polycyclic aromatic hydrocarbons (PAH), some of which cause cancer. 35 PAHs are widespread toxic pollutants that are formed during incomplete combustion or pyrolysis of organic material. 35 Cancer-causing PAHs such as benzo[a]pyrene are found in tobacco smoke (see Section 12.4.3.6). Sixteen PAHs are on the FDA’s list of harmful and potentially harmful constituents of tobacco. 24

Studies from independent researchers have detected relatively low levels of PAHs in the emissions of heated tobacco products ( Table 18B.5.1). These include benzo[a]pyrene, benz[a]anthracene and pyrene. 26 , 27 , 32 Sixteen different PAHs were detected in the emissions from IQOS in one study. 26

Aldehydes

Aldehydes are a group of organic (carbon-based) molecules that include formaldehyde and acrolein gas. Many aldehydes are toxic to the respiratory system and some are known to cause cancer (see Section 12.4.3.1). There are five aldehydes on the FDA’s list of harmful and potentially harmful constituents of tobacco. 24

Aldehydes in smoke are generated from thermal decomposition, such as pyrolysis and other chemical reactions that occur at lower temperatures than combustion. They can be formed once temperatures approach 200°C, 17 which occurs during use of most heated tobacco products (see InDepth 18B.1.2). Many independent studies have detected the presence of aldehydes in the emissions from heated tobacco products. 17 , 26 , 27 , 32 , 33 , 36 , 37 One study found acetaldehyde, acrolein (acrylaldehyde), benzaldehyde, crotonaldehyde, formaldehyde, isovaleraldehyde and propionaldehyde in the emissions of heated tobacco products. 26 Levels of aldehydes in heated tobacco emissions are generally closer to those in cigarette smoke compared to TSNAs and PAHs (see Table 18B.5.1). 26 , 27 Aldehyde levels increased dramatically with increases in temperature used to generate emissions. 38

Other toxic substances

Additional toxic chemicals from the FDA’s list of harmful and potentially harmful constituents of tobacco that have been detected in the emissions of heated tobacco products include acetamide, acetone, acrylonitrile, 1- and 2-aminonaphthalene, 4-aminobiphenyl, ammonia, benzene, 1,3-butadiene, cresols, ethylene oxide, furans (including 2-furanmethanol, 2(5H)-furanone, and 5-methylfurfural), isoprene, mercury, naphthalene, phenol, polonium-210, propylene oxide, quinoline, selenium, toluene and o-toluidine (see Table 18B.5.1). 26 , 27 , 32 , 36 , 39-43 Other chemicals found in the emissions with known toxicity include furfural, diacetyl and glycidol, glyoxal, methylglyoxal, pyridine and 4-ethenylpyridine. 33 , 36 , 41 These chemicals are mostly found at lower concentrations than in the emissions of conventional cigarettes but higher than e-cigarettes. The extent of toxicity at these lower concentrations is not well understood. 

A study of metals in side-stream emissions from IQOS detected aluminium, titanium, strontium, molybdenum, tin and antimony, but no lead or cadmium. However, overall metal levels in these emissions were no higher than background (ambient) levels. 2

A study of four different heated tobacco products bought in Japan found that ammonia was present in the emissions. The amount of ammonia detected increased when the heating temperature increased. 40 Ammonia and ammonium compounds are common additives that increase the pH and increase the attractiveness of tobacco (see Section 12.6.2.1).

Emissions from nine different commercially available brands of tobacco sticks for IQOS with a range of flavours were compared in a study that examined toxic constituents. Some of the differently flavoured tobacco sticks emitted higher levels of tobacco-specific nitrosamines and formaldehyde levels than others, but there were no significant differences in the levels of nicotine and other assessed aldehydes. 33

18B.5.3.3 Other chemicals

Heated tobacco products are available with characterising flavours, such as menthol, bubble gum, lime, lemon ginger, cherry, grape, apple, mint, and apricot. 17 These flavours are produced by additives and are likely increase the attractiveness of the product to the consumer.

Tobacco sticks are also available for heated tobacco products that contain squeezable capsules that release flavour. Some websites sell separate capsules that can be inserted into the tobacco sticks used in heated tobacco products. A study of the emissions of seven different heated tobacco products, once the flavour capsules were broken, showed that this event led to an eight-fold increase in total volatile organic compounds. 44 Ethyl butyrate, isoamyl acetate and limonene were the most common of these compounds. The levels of one compound, diacetyl, exceeded the maximum daily intake limit by between 3 and 5-fold, according to the US National Institute for Occupational Safety & Health (NIOSH) guidelines. 44

 

Table 18B.5.1 Non-exhaustive list of chemicals detected in the smoky emissions from heated tobacco products, their toxicity, relative amount in emissions and relative exposure (from biomarkers of exposure, BoE) compared to conventional cigarettes

Chemical

Type

FDA list a

SCENIHR list b

IARC group c

Proportion of chemical compared to that found in cigarette smoke

Proportion of BoE compared to that detected in cigarette smokers d

Acetaldehyde

Aldehyde

CA, RT, AD

 

2B

12 – 23%

 

Acetamide

Carbonyl

CA

 

2B

23%

 

Acetone

Carbonyl

RT

 

 

4 – 13%

 

Acrolein

Aldehyde

RT, CT

 

2A

4 – 82%

26 – 53%

Acrylamide

Carbonyl

CA

 

2A

35%

 

Acrylonitrile

Organic compound

CA, RT

 

2B

<1%

13 – 21%

4-Aminobiphenyl

Aromatic amine

CA

 

1

<1%

15 – 41%

1-Aminonaphthalene

Aromatic amine

CA

 

 

<1%

4 – 6%

2-Aminonaphthalene

Aromatic amine

CA

 

 

<1%

11 – 19%

Ammonia

Inorganic

RT

INU

 

22 – 37%

 

Benzaldehyde

Aldehyde

 

TAB, TUB

 

50%

 

Benz[a]anthracene

Polycyclic aromatic hydrocarbon

CA, CT

 

2B

5 – 11%

 

Benzo[a]pyrene

Polycyclic aromatic hydrocarbon

CA

 

1

4 – 9%

28 - 30%

Benzo(b)fluoranthene

Polycyclic aromatic hydrocarbon

CA, CT

 

 

5%

 

Benzo(c)phenanthrene

Polycyclic aromatic hydrocarbon

CA

 

 

680%

 

Benzo[k]fluoranthene

Polycyclic aromatic hydrocarbon

CA, CT

 

2B

18%

 

Benzene

Hydrocarbon

CA, CT, RDT

 

1

1%

6 – 16%

Benzyl alcohol

Aromatic alcohol

 

TUB, INU

 

2% - 24%

 

Black carbon

Carbon lattice

 

 

2B

<1%

 

1,3-Butadiene

Hydrocarbon

CA, RT, RDT

 

1

<1%

8 – 23%

Butanal

Carbonyl

 

 

 

29 – 58%

 

Butyraldehyde

Aldehyde

 

 

 

26%

 

Carbon monoxide

Toxic gas

RDT

 

 

1%

23 – 47%

Carbon dioxide

Toxic gas

 

 

 

5%

 

Cresols

Phenols

CA, RT

 

 

1 – 2%

 

Crotonaldehyde

Aldehyde

CA

 

2B

4 – 24%

23 – 43%

Chrysene

Polycyclic aromatic hydrocarbon

CA, CT

 

2B

6%

 

Diacetyl

Organic compound

 

CF, TUB

 

15 – 87% e

 

Dibenz[a,h]anthracene

Polycyclic aromatic hydrocarbon

CA

 

2A

2%

 

Dibenzo[a,e]pyrene

Polycyclic aromatic hydrocarbon

CA

 

3

<1%

 

Dibenzo(a,l)pyrene

Polycyclic aromatic hydrocarbon

CA

 

2A

50%

 

Ethyl butyrate

Carbonyl

 

 

 

 

 

Ethylene oxide

Organic compound

CA, RT, RDT

 

1

<1%

32 – 51%

Formaldehyde

Aldehyde

CA, RT

 

1

18 – 74%

 

Furfural

Organic compound

 

TUB

3

2% - 209% f

 

2-Furanmethanol

Organic compound

 

 

 

3 – 1095% f

 

2(5H)-Furanone

Organic compound

 

 

2B

21 - 267%

 

Glycidol

Organic compound

 

 

2A

324%

 

Glyoxal

Aldehyde

 

 

 

13%

 

Indeno[1,2,3-cd]pyrene

Polycyclic aromatic hydrocarbon

CA

 

2B

3%

 

Isoamyl acetate

Carbonyl

 

 

 

 

 

Isovaleraldehyde

Aldehyde

 

 

 

41%

 

Isoprene

Hydrocarbon

CA

 

2B

<1%

 

Lead

Toxic metal

CA, CT, RDT

 

2B

7%

 

Limonene

Hydrocarbon

 

 

3

0.5% - 133%?

 

Linalool

Organic compound

 

INU, TUB, CF

 

17% - 10,833% f

 

Menthol

Organic compound

 

INU, CF

 

21% - 37,777% f

 

Mercury

Toxic metal

CA, RDT

 

3

37%

 

5-Methylchrysene

Polycyclic aromatic hydrocarbon

CA

 

2B

<1%

 

Methyl ethyl ketone

Carbonyl

RT

 

 

3 – 39%

 

5-Methylfurfural

Organic compound

 

 

 

157% - 583% f

 

Methylglyoxal

Carbonyl

 

 

3

50%

 

Naphthalene

Polycyclic aromatic hydrocarbon

CA, RT

 

2B

2%

 

Nicotine

Alkaloid

RDT, AD

 

 

33 – 84% f

85 – 113%

NAB ( N'-Nitrosoanabasine)

Tobacco-specific nitrosamine

 

 

3

8 – 27%

 

NAT ( N'-Nitrosoanatabine)

Tobacco-specific nitrosamine

 

 

3

6 - 7%

 

NNK (4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

Tobacco-specific nitrosamine

CA

 

1

3 – 4%

33 – 52%

NNN ( N-Nitrosonornicotine)

Tobacco-specific nitrosamine

CA

 

1

4 – 5%

12 – 30%

Nitric oxide

Toxic gas & free radical

 

 

 

3 – 6%

 

Phenol

Phenols

RT, CT

 

3

4 - 9%

 

Polonium-210

Radioactive metal

CA

 

 

10%

 

Propionaldehyde

Aldehyde

RT, CT

 

 

9 – 26%

 

Propylene oxide

Organic compound

CA, RT

 

2B

16%

 

Pyrene

Polycyclic aromatic hydrocarbon

 

 

3

6 – 15%

38 – 57%

Pyridine

Organic compound

 

 

2B

21%

 

Quinoline

Organic compound

CA

 

2B

<2%

 

Selenium

Mineral element

RT

 

3

 

 

Styrene

Organic compound

CA

 

2A

4%

 

Toluene

Hydrocarbon

RT, RDT

 

3

1%

 

o-Toluidine

Organic compound

CA

 

1

1%

41 – 58%
  1. For chemicals on the FDA’s list of Harmful or Potentially Harmful Constituents (HPHC) in tobacco, the FDA’s health concerns associated with the substance are listed as: carcinogen (cancer-causing) (CA), respiratory toxicant (RT), cardiovascular toxicant (CT), reproductive or developmental toxicant (RDT), addictive (AD). 24
  2. For chemicals listed as Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) priority substances, the health concerns according to SCENIHR are listed as INU: increases inhalation or nicotine uptake (potentially increasing addictiveness), CF: characterising or potentially characterising flavour, TUB: toxic or potentially toxic in unburnt form, TAB: toxic or potentially toxic after burning. 45
  3. International Agency for Research on Cancer (IARC) designations as to the strength of evidence for carcinogenicity to humans are Group 1: Carcinogenic to humans, Group 2A: Probably carcinogenic to humans, Group 2B: Possibly carcinogenic to humans, Group 3: Not classifiable as to its carcinogenicity to humans. 46 , 47
  4. Comparisons did not include data from carbon-tipped heated tobacco products, which are atypical and now rare.
  5. Data come from a heated tobacco product with a flavour capsule.
  6. Data include comparisons of a mentholated heated tobacco product to a non-mentholated reference cigarette.

 

Sources: Acetaldehyde, 10 , 26 , 27 , 32 Acetamide, 32  Acetone, 10 , 27 , 32 Acrolein, 10 , 26 , 27 , 32 Acrylamide, 32 Acrylonitrile, 27 , 32 4-Aminobiphenyl, 27 , 32 1-Aminonaphthalene, 27 , 32 2-Aminonaphthalene, 27 , 32 Ammonia, 10 , 32 Benzaldehyde, 26 Benz[a]anthracene, 27 , 32 , 48 Benzo[a]pyrene, 27 , 32 Benzo(b)fluoranthene, 48 Benzo(c)phenanthrene, 48 Benzo[k]fluoranthene, 48 Benzene, 10 , 27 , 32 Benzyl alcohol, 41 Black carbon, 2 1,3-Butadiene, 10 , 27 , 32 Butanal, 10 Butyraldehyde, 32 Carbon monoxide, 27 , 32 , 49 Carbon dioxide, 49 Cresols, 32 Crotonaldehyde, 10 , 26 , 27 , 32 Chrysene, 48 Diacetyl, 44 Dibenz[a,h]anthracene, 48 Dibenzo[a,e]pyrene, 48 Dibenzo(a,l)pyrene, 48 Ethyl butyrate, 44 Ethylene oxide, 27 , 32 , Formaldehyde, 10 , 26 , 32 Furfural, 32 , 41 2-Furanmethanol, 32 , 41 2(5H)-Furanone, 32 , 41 Glycidol, 32 Glyoxal, 48 Indeno[1,2,3-cd]pyrene, 48 Isoamyl acetate, 44 Isovaleraldehyde, 26 Isoprene, 10 , 32 Lead, 32 Limonene, 44 Linalool, 41 , 44 Menthol, 41 Mercury, 32 5-Methylchrysene, 48 Methyl ethyl ketone, 10 , 32 5-Methylfurfural, 32 , 41 Methylglyoxal, 48 Naphthalene, 48 Nicotine, 27 , 32 , 41 NAB ( N'-Nitrosoanabasine), 10 , 32 NAT ( N'-Nitrosoanatabine), 10 , 32 NNK (4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone, 10 , 27 , 32 NNN ( N-Nitrosonornicotine), 10 , 27 , 32 Nitric oxide, 27 , 32 Phenol, 10 , 32 Polonium-210, 42 , 43 Propionaldehyde, 10 , 26 , 27 , 32 Propylene oxide, 32 Pyrene, 27 , 32 Pyridine, 32 Quinoline, 32 Selenium, 32 Styrene, 32 Toluene, 32 o-Toluidine. 27 , 32

18B.5.4 Heated tobacco product emissions compared to cigarettes and e-cigarettes

Comparison to cigarette smoke

Many studies published by the tobacco industry have reported that the levels of harmful substances in heated tobacco emissions are lower than those from conventional cigarettes. There are sufficient publications from independent scientists to address this topic, which are reported on in this subsection. In general, independent researchers have also found that many harmful substances are present in relatively lower amounts in the emissions of heated tobacco products. However, there is also evidence that there are some chemicals that are present at much higher levels than in tobacco smoke. 32

The amount of specific chemicals in heated tobacco emissions compared to that found in reference cigarette smoke are presented in Table 18B.5.1 in the sixth column. Ranges are reported for many of the chemicals, reflecting the different testing conditions, different products and different reference cigarettes used for comparisons. Most of the chemicals with toxicity concerns are found in lower amounts in heated tobacco products. 10 , 17 , 26 , 27 , 32 , 42 , 43 , 48

Tobacco-specific nitrosamines (TSNAs), which are usually produced during the curing and aging of tobacco, are found in relatively low amounts in heated tobacco emissions compared to cigarette smoke. The most concerning TSNAs that cause cancer, NNK and NNN, are found at 3 – 4% and 4 to 5% of levels in cigarette smoke, respectively. 10 , 27 , 32

Heated tobacco products generally contain higher relative levels of aldehydes (26% - 82% of that in tobacco smoke, see Table 18B.5.1) than they do TSNAs (4% - 27% of that in tobacco smoke). Aldehydes are produced during heating by chemical reactions such as pyrolysis, which occur at lower temperatures, consistent with their production in heated tobacco products. Formaldehyde is found in heated tobacco emissions at between 18 and 74% of the amounts found in cigarettes smoke, while acrolein is found at 4 to 82% and propionaldehyde at 9 to 26%. 10 , 26 , 27 , 32

Polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, are a group of carcinogenic (cancer-causing) chemicals found in tobacco smoke (see Section 12.4.3.6). They are typically produced during combustion chemical reactions. Although these are found in the emissions of heated tobacco products, they are usually at quite low levels compared to those found in cigarette smoke. However, one PAH, benzo(c)phenanthrene, was found at almost seven-fold higher levels in heated tobacco emissions compared to cigarettes. 48

The chemicals found at higher levels in heated tobacco emissions include benzo(c)phenanthrene, furfural, 2-furanmethanol, 2(5H)-furanone, glycidol, linalool, and 5-methylfurfural. 32 , 41 , 44 , 48 One study has identified 56 chemicals that are present at higher levels in heated tobacco emissions than cigarette smoke. 32

Comparison to e-cigarette emissions

A study has compared toxic chemicals in IQOS mainstream emissions to those in aerosols from three different e-cigarettes. 48 For all but one of the chemicals (naphthalene), the heated tobacco emissions contained higher levels of each chemical than the e-cigarette emissions. Some of the largest differences were seen in aldehydes, with heated tobacco products producing 166- to 833-fold higher amount of acetaldehyde than the e-cigarettes. These differences were smaller for PAHs, such as benzo(a)pyrene, which was found at 23- to 42-fold higher in heated tobacco compared to e-cigarette emissions. 48

18B.5.5 Secondhand emissions from heated tobacco products

Secondhand emissions are those inhaled by people in the near vicinity of tobacco use. For cigarettes and other tobacco products that are smoked, there is considerable evidence that exposure to secondhand smoke causes many diseases and mortality in non-smokers—refer to Chapter 4 . To date, there are no long-term studies on the health effects of exposure to secondhand emission from heated tobacco products.

Secondhand emissions from conventional cigarettes are a mix of sidestream emissions, emissions exhaled by users and any emissions that emanate from the device during puffing that are not directly inhaled (see Section 12.4.1.2). There does not appear to be a formal definition of secondhand emissions from heated tobacco products, although one review has defined these emissions as a combination of sidestream and exhaled mainstream emissions. 8

Approximately half of the studies of the chemistry of secondhand emissions from heated tobacco products have been conducted by the tobacco industry. 9 This section will present data from independent studies and a brief comparison of results.

There is no standard protocol for the measurement of secondhand emissions from heated tobacco products, but various research groups have used similar bespoke methods. In most studies, portable monitors were used to detect particulate matter or specific chemicals in homes or cars when these tobacco products were used. 50 Alternatively, dedicated test rooms were used where parameters such as airflow, temperature and humidity were controlled in order to create a more standardised test. 3 , 51 Factors such as air temperature and air-conditioning fans affected the size range of aerosol particles. 52 As most of the chemicals found in tobacco emissions are also found in indoor and outdoor ambient air, only those that are found above background levels are considered relevant.

In a home setting, heated tobacco products produced approximately 4- to 5-fold higher than background levels of PM 1, PM 2.5 and PM 10 and ultrafine particles (see InDepth 18B.5.1.1 for explanations of terminology). 50 PM levels were approximately double the background levels once heated tobacco was used inside a car. Carbon monoxide levels were found to increase above background in the car but not in a house setting. Levels of pollutants from heated tobacco in this study were consistently lower than those from cigarettes. Similar results were found in another study, showing roughly double the amount of PM pollution after use of IQOS and Glo in a dedicated test room. 53 Higher-than-baseline levels of PM were demonstrated in one study at least one hour after use had ceased. 54

The secondhand emissions of heated tobacco products have been shown to contain above- background levels of acrolein, acrylaldehyde benzene, black carbon, formaldehyde nicotine, organic acids, and toluene. 2 , 36 , 55

A systematic review of the literature predicted that heated tobacco products use exposes users and bystanders to considerably lower, but still measurable levels, of particulate matter and toxic chemicals that are also found in cigarette smoke. 8 Another systematic review that compared industry to independent studies found general agreement that IQOS emitted lower levels of emissions compared to conventional cigarettes, but also that both types of studies had found emissions of low levels of toxic chemicals, including those on the FDA’s list of harmful and potential harmful constituents of tobacco. 9

18B.5.6 Biomarkers of exposure to chemicals from heated tobacco products

Exposure to the chemicals from cigarette smoke causes a wide range of serious diseases, most of which take years, if not decades, to develop—see Chapter 3. For relatively new tobacco products such as heated tobacco, biomarkers of exposure to toxic chemicals are an important indicator of the potential for damage and disease in the future.

A biomarker of exposure is a substance in the human body that can be measured in a test that will indicate exposure to specific chemicals. Biomarkers of exposure can be used to test for exposure to specific chemicals and in different regions of the body. Biomarkers of potential harm can be used to detect damage done by exposure to all the chemicals in tobacco products, which may lead to disease. See InDepth 18B.6.1 for more about biomarkers of potential harm in users of heated tobacco products. It is important to note that a person is exposed to many different chemicals over their lifetime, not just from tobacco. Information from biomarkers is therefore more useful in comparing people who use different types of tobacco products, or non-smokers to smokers. Unfortunately, most studies on biomarkers of exposure for heated tobacco users compare them to users of cigarettes. Most of these studies have been performed by the tobacco industry. A comparison to non-smokers would be more informative for predicting the health effects of heated tobacco use.

Measures of total nicotine equivalents (see Section 12.5.6.4) found in the urine of users have shown that users of heated tobacco products take in similar amounts of nicotine to those taken in by users of cigarettes. This has been shown by studies performed or funded by the tobacco industry, as well as by independent studies. 27 , 56-58

Carbon monoxide levels in the emissions of heated tobacco products are much lower than for cigarettes. Despite these low levels, exhaled carbon monoxide was increased for non-smokers immediately after use of an IQOS. A study has shown that non-smokers’ exhaled carbon monoxide rose from an average 1.5 ppm (parts per million) before use to 4.12 ppm after IQOS use, compared to smokers who saw a rise from an average of 2.5 ppm to 4.9 ppm after IQOS use. 59 Exhaled carbon monoxide was found to be 23 to 45% reduced in the breath of heated tobacco product users compared to people who smoke cigarettes. 27

Biomarkers for tobacco-specific nitrosamines (TSNAs) are particularly useful for measuring exposure. As there is no background level of these chemicals from other sources, the levels measured in the body are a good indicator or exposure to substances emanating from tobacco products as opposed to any other source. Studies of biomarkers of exposure for NNN and NNK show consistently lower levels in users of heated tobacco products compared to cigarettes. 27 Most of this research comes from tobacco industry studies. There are findings that indicates the amount of some chemicals present in the emissions compared to that in cigarette smoke is not necessarily a good prediction of the relative amount that enters the body. Biomarkers of exposures for NNK in users of heated tobacco are 33 to 44% that of cigarette smokers, which is not as low as expected given the 3 to 4% present in the heated tobacco emissions (see Table 18B.5.1). Similar results were found for NNN. Since these chemicals are only present in tobacco products, other pollutants cannot be contributing to the levels shown by these biomarker measurements, however, exposure to secondhand smoke may have contributed.

Biomarkers of exposure for numerous other toxic chemicals follow a similar pattern to those for NNN and NNK described above ( Table 18B.5.1). These include benzene (at 6 to 16% of that in cigarette smokers), aromatic amines (such as 4-aminobiphenyl at 15 to 41% that of cigarette smokers) and numerous polycyclic aromatic hydrocarbons (such as benzo[a]pyrene, which is 28 to 30% of that in cigarette smokers). 27  

Relevant news and research

For recent news items and research on this topic, click here. (Last updated October 2024)

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