There are "significant gaps" in research on the regulation and sales of e-cigarettes, a former health minister has said.
Norman Lamb, who is chairman of the Science and Technology Committee, said there needs to be better understanding of the implications of the "growing industry" of electronic cigarettes.
The comments come as the Committee launched an inquiry into the products.
The probe will look at the impact of e-cigarettes on human health, the "suitability" of regulations guiding their use, and the financial implications of their use on business and the NHS.
Mr Lamb said: "Almost three million people in the UK now use e-cigarettes, but there are still significant gaps in the research guiding their regulation and sale.
"They are seen by some as valuable tools that will reduce the number of people smoking 'conventional' cigarettes, and seen by others as 're-normalising' smoking for the younger generation.
"We want to understand where the gaps are in the evidence base, the impact of the regulations, and the implications of this growing industry on NHS costs and the UK's public finances."