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25.10.2021 |News

Tests of e-liquids and e-vapour yield questionable results

New analyses from Australia and the USA show that there are countless chemical components in e-liquids and e-vapour, some of which are of concern. They thus confirm older analyses and point to possible further problematic substances. They also make it clear that most of the existing chemical components have not yet been identified and their hazard potential is unknown.

Picture: E-cigarette liquid container

In an analysis published in 2019, the team around Professor Alexander Larcombe tested nicotine-free e-liquids in Australia. The results at that time were already surprising and alarming. Of the 10 liquids tested, 60% contained nicotine and some of these in amounts that could not be explained by simple impurities. In all samples, the researchers found 2-chlorophenol - a chemical often used in pesticides and disinfectants and known to irritate the skin and lungs. Furthermore, most of the e-liquids tested contained 2-aminooctanoic acid, an amino acid found in faeces, urine and blood of mammals. The results prompted the team to extend the series of tests.

Confirmation of the questionable results

In the present analysis, 65 e-liquids were tested. All of the e-liquids tested were purchased online or in shops in Australia. All were advertised as "best sellers" manufactured in Australia and nicotine-free, so they are likely to be representative of what many Australian e-cigarette users use. For the new series of tests, the e-liquids were also heated to simulate the consumption of the liquids and to test which new substances are produced under these circumstances.

During the tests, the research team found a number of chemical flavourings, many of which are classified as "generally safe" when used in food and beverages. However, the long-term consequences of inhaling these substances are unknown.

Traces of nicotine were again detected, but in fewer samples and in lower concentrations. The authors assume that this is an indication that the production of liquids has become cleaner in the meantime. It could also be due to the fact that only so-called "free" nicotine was tested and not the nicotine salts that are widely used today.

The research team also found various chemicals of concern such as 2-chlorophenol, benzaldehyde, trans-cinnamaldehyde and menthol. 2-chlorophenol, however, was only found in about half of the e-liquids tested. Benzaldehyde was found in all but four of the e-liquids, while menthol and trans-cinnamaldehyde were present in about threequarters of the e-liquids.

The presence of these chemical flavourings is a concern for several reasons:

  • All of the chemicals mentioned are known to alter the effects of nicotine. Menthol increases the addictive potential of nicotine.
  • Benzaldehyde and trans-cinnamaldehyde are known to inhibit an enzyme called CYP2A6. CYP2A6 is crucial for the breakdown of a wide variety of substances in the human body. Inhibition of this enzyme results in nicotine remaining longer in the body of e-cigarette users.
  • Benzaldehyde is also an irritant for the respiratory tract and impairs the immune defence in lung infections. Trans-cinnamaldehyde has even stronger effects on the immune cells in the lungs.
Chemical fingerprint

A research team at Johns Hopkins University has gone even further in the analysis of e-liquids and e-vapor and made a complete chemical fingerprint of the tested products. So far, the analyses of e-liquids and e-vapour have been limited to known substances that also occur in cigarette smoke. These analyses are also the basis for the claim that e-cigarettes are less harmful than cigarettes. The fact that other toxic substances could also be present in e-liquids and e-vapour was disregarded.

E-liquids with tobacco flavouring from four popular brands in the USA (Mi-Salt, Vuse, Juul and Blu) were analysed. In their analysis, Mina Tehrani's team found nearly 2,000 chemicals in e-liquids and e-vapour, the vast majority of which were not identified. Of those that the team was able to identify, six substances were potentially harmful, including three chemicals that had never been found in e-cigarettes before. The team was particularly surprised to find the stimulant caffeine in two of the four products. Caffeine has already been detected in e-cigarettes, but only in caffeine-containing flavours such as coffee and chocolate. This raises the question of whether the caffeine was added intentionally and with what intent. In addition to caffeine, the team found three industrial chemicals, a pesticide and two flavourings associated with possible toxic effects and respiratory irritation.

No new findings

Back in 2016, an analysis by Sleiman et al proved that several chemical compounds are found in e-vapour that are of concern due to their potentially harmful effects on users and passively exposed non-users. These chemical emissions are associated with both carcinogenic and non-carcinogenic health effects. In addition to aldehydes and other volatile organic compounds, researchers have noted the presence of propylene oxide in e-liquids and glycidol in vapours. Both compounds are considered possible or probable carcinogens.

Too many unknowns

The results of the analyses from Australia and the USA clearly show one thing above all – how little we currently know about the chemical components of e-liquids and e-vapour. It is not only the number of substances found that is alarming, but also the fact that a large part of them have not been identified. This unknown makes a useful risk analysis of e-cigarette consumption impossible. It is quite possible that there are other harmful substances among the unidentified substances. Moreover, the Australian study shows that in addition to known harmful substances, there are also substances whose possible health consequences from inhalation exposure are unknown.

The studies clearly prove one thing: the use of e-cigarettes is not risk-free for the health of consumers, only the extent of the risk remains unknown.


Larcombe, Alexander; Allard, Sebastien; Pringle, Paul; Mead-Hunter, Ryan; Anderson, Natalie; Mullins, Benjamin (2021): Chemical analysis of fresh and aged Australian e-cigarette liquids. In The Medical journal of Australia. DOI: 10.5694/mja2.51280.

Sleiman, Mohamad; Logue, Jennifer M.; Montesinos, V. Nahuel; Russell, Marion L.; Litter, Marta I.; Gundel, Lara A.; Destaillats, Hugo (2016): Emissions from Electronic Cigarettes: Key Parameters Affecting the Release of Harmful Chemicals. In Environ. Sci. Technol. 50 (17), pp. 9644–9651. DOI: 10.1021/acs.est.6b01741.

Tehrani, Mina W.; Newmeyer, Matthew N.; Rule, Ana M.; Prasse, Carsten (2021): Characterizing the Chemical Landscape in Commercial E-Cigarette Liquids and Aerosols by Liquid Chromatography-High-Resolution Mass Spectrometry. In Chem. Res. Toxicol. DOI: 10.1021/acs.chemrestox.1c00253.

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