A health ministry research group found Thursday that four of the nine electronic cigarettes sold in Japan produce vapor with high levels of formaldehyde, a known carcinogen.
A panel at the Health, Labor and Welfare Ministry that received a report on the findings said "negative health effects" cannot be ruled out from the use of e-cigarettes.
The ministry is expected to study the feasibility of tightening regulations, officials said.
Powered by batteries, e-cigarettes vaporize liquids that have different flavors, such as vanilla and various fruits.
In the survey, five types of liquid solution were vaporized from each of the nine e-cigarettes purchased in Japan last year. Four devices produced roughly the same or higher concentrations of formaldehyde than detected in smoke from regular cigarettes.
The researchers believe formaldehyde was produced because the liquids become oxidized when heated, and the mechanism of each atomizer played a part in producing the different amounts.
The research group also examined the 103 liquid solutions available in Japan that were touted as nicotine-free and found nicotine in 48 of them. Although the majority of the liquids had barely measurable amounts in them, the substance is still banned in e-cigarettes by domestic law.
E-cigarettes caught the attention of Japanese smokers in 2010, when Japan raised the tax on cigarettes.
Some 6.6 percent of about 8,000 respondents in a survey between 15 and 69 said they had used e-cigarettes, according to the researchers.
The global market for e-cigarettes has also been expanding, with at least 46 vaporizers and 7,700 liquid solutions up for sale.