Over 35m people worldwide now use e-cigarettes, according to one estimate. In the US, this includes 4.5% of the adult population. But the rise in vaping has led to a trade in fake e-liquids – the mix of water, glycerol, propylene glycol, flavours and (usually) nicotine used to create the vapour of e-cigarettes.

Fake e-liquids are those that contain ingredients or incorrect concentrations of them that do not match those on the label. In particular, fakes often contain less or more nicotine than their labels claim, or impurities such as other drugs. [...]