Experts have called for more regulation of chemicals used to flavour e-cigarettes after a study found levels of up to twice recommended exposure limits.
Manufacturers say that the flavourings used in e-cigarettes are mostly the same as those used in food and sweet manufacturing, and are therefore safe.
However, the researchers said the safety related to eating the chemicals, rather than inhaling them, and the chemicals could act as respiratory irritants.
The study, published online in the journal Tobacco Control, took a sample of 30 products on sale in the US, including disposable brands and refill bottles, in flavours such as tobacco, menthol, vanilla, cherry, coffee, bubble gum and chocolate.
In 13 of the products, flavouring chemicals made up more than one per cent