The levels of chemicals used to flavour e-cigarette fluid exceed recommended exposure limits and some could be respiratory irritants,  research suggests.

Writing in Tobacco Control the authors from Portland State University argue for regulation which should include compulsory ingredient listing, limiting the levels of certain flavourings and the total permissible levels of flavourings.

The researchers tested 30 products with flavours ranging from menthol, vanilla, cherry and coffee, chocolate/cocoa, grape, apple, cotton candy and bubble gum.

Flavouring chemicals totalled more than 1% by volume in 13 of the 30 liquids analysed, levels greater than 2% by weight in seven liquids, and levels greater than 3% by weight in two products.

Six of the 24 compounds in the analysis were aldehydes, a compound class recognised toxicologically to be ‘primary irritants’ of the mucosa of the respiratory tract.

Using a consumption rate of around 5 ml/day typically reported on online vaping forums, vapers would be exposed to twice the recommended occupational exposure limits of benzaldehyde and vanillin with the products tested, they say.

“And toxic degradation products may be produced by reaction of the flavour chemicals at the high temperatures present during vaping,” they caution.

While the results are limited by sample size they are likely to be similar to what a broad survey would have revealed, they say.

Their findings suggest that “very high levels of some flavour chemicals are undoubtedly present in a great number of the thousands of products currently available.”