But health experts are rightly worried that these devices might make it easy for teenagers to develop an addiction to nicotine, which can be toxic at high doses and impairs brain development in children. Lab tests by the F.D.A. have also found that some electronic cigarettes contain dangerous chemicals that are used in antifreeze.

That is why an overwhelming majority of the European Parliament voted to ban advertising of electronic cigarettes and limit the amount of nicotine in each device to 20 milligrams per milliliter, similar to ordinary cigarettes. Makers of these devices, which now include large tobacco companies, will also have to put warning labels that include information about their addictiveness and toxicity on their packaging and must make electronic cigarettes childproof. The rules, which will go into effect in 2016, also regulate the purity of the nicotine liquid in the devices.

These rules strike a good balance.