A study about E-Liquid flavours published in the Harm Reduction Journal has found that the “vast majority of flavouring compounds in e-cigarette liquids were present at levels far lower than needed to classify them as toxic”. However one exception was found: some E-Liquids containing flavouring with methyl cyclopentenolone presented at a potentially high level - enough to be classified as toxic according to EU guidelines that determine toxicity based on LD50 values for exposure to each substance.
Most flavours tested in the study were classified as GRAS (generally recognised as safe) under EU regulations. However, concern lies around the fact that these flavourings are developed for ingestion rather than inhalation and safety may vary across consumption method.
Many chemicals used in products for human consumption are classified as toxic. For example, ethyl vanillin is a flavouring used in many food products. Ethyl vanillin has an oral intake toxicity classification: harmful if swallowed. However, it is still widely used in the food industry. In Europe alone 44 tonnes is used in food products annually while 330 tonnes per year is used in the USA.
Toxicity for consumption is not based on chemical presence alone but on the concentration in the finished product. In the same way, E-Liquids will contain chemicals that are technically classified as toxic as the flavourings within these products are from the food industry.
Although almost all flavourings tested were not toxic, the research concludes that “since exceptions exist, regulatory monitoring of liquid composition is warranted.”