Among those who currently using e-cigs, 98.6 per cent of children and 95.2 per cent of young adults said that their first one was flavoured, according to an American study.
If flavours were not available, 77.8 per cent of adolescents and 73.5 per cent of young adults who used e-cigarettes said they wouldn't use them.
It is estimated that there are more than 7,500 flavours of e-cigarettes available on the market.
Many are sweet flavours and taste like fruit or dessert, according to researchers.
Though e-cigs are typically marketed as a harmless alternative to traditional cigarettes, previous research has shown they are not free from harmful chemicals.
Chemicals and carcinogens - such as acetaldehyde, formaldehyde and tobacco-specific nitrosamines which are common in cigarettes - have been found in e-cigarettes.
The findings were based on a study of 2,483 12 to 17-year-olds and 4,326 young adults ages 18 to 29 in four areas of Texas.
Doctor Melissa Harrell, an associate professor at the University of Texas School of Public Health, said: "Our study supports a growing body of evidence that suggests the use of flavours in tobacco products, such as e-cigarettes, are appealing to youth and young adults.
"What is most surprising is that before this, no one has yet asked young people, 'if flavours were removed from these products, would you continue to use them?'"
Dr Harrell added: "Taste is an important factor.
"These flavours mask the flavour of tobacco, which can have a harsh taste."
The findings were part of a series of papers by University of Texas researchers published in the journal Tobacco Regulatory Science.
In a second study, researchers found that advertising could have a significant role in the uptake of vaping among children.
From 2011 to 2013, e-cigarette adverts on TV in the US increased by more than 250 per cent and reached more than 24 million teenagers, according to the research.
In 2014, 70 percent of middle and high school students in the United States had seen an e-cig advert on TV, in a retail store, on the internet or in newspapers and magazines.
The second study shows that children in Texas who see an e-cig advert in a retail store or on the internet are more likely to start using them or be susceptible to them in the future.
In 2015, nearly three million middle and high school students in the US were e-cig users, according to official figures.