New York, Oct 4 (IANS): The use of e-cigarette has tripled among middle and high school students from 2013 to 2014, according to data from the 2014 National Youth Tobacco Survey. Now, a new study has found that it is partly due to aggressive online marketing by e-cigarette vendors.

The study by University of California-San Diego researchers described marketing tactics that make purchasing e-cigarettes easy for all ages.

"We found e-cigarette vendors were highly engaged in promoting the culture of 'vaping' online, including posting images to Instagram, a social media site used by 52 percent of teens," said study's first author Tim K. Mackey.

"Despite the fact that 47 states prohibit the sale of e-cigarettes to minors, the results highlight the potential of the internet to encourage e-cigarette initiation and underage purchasing," he added.

E-cigarettes are tobacco-less, battery-operated devices that spritz vapour into the mouth with flavours like bubble gum and peach fuzz.

Users of these devices, known colloquially as "vapers", exhale a mixture of volatile organic compounds, heavy metals and ultrafine particles that usually contain aerosolised nicotine in a cloud of vapour.

Researchers found that although some of e-cigarette vendors did display health warnings about the devices on their website, but the notices were often depicted in smaller fonts or placed discretely in the terms and conditions section of a website.

One third of the vendors had no detectable age verification process for buyers and of those that did, most required only a simple click to say the buyer was within the legal age limit.

"The study found that online e-cigarette vendors use a variety of sophisticated and aggressive marketing practices, including promotional offers and high social media engagement to promote the sale of their products," Mackey said.

The findings were published in the journal Drug and Alcohol Dependence.