The Department of Environmental Health-National Institute of Public Health in Japan recently published a study that claims that e-cigs and other vaping devices have 10 times the amount of certain carcinogens found in tobacco cigarettes. Most notably, the researchers found formaldehyde and acetaldehyde in the vapor, which is created from the heated liquid in the device.

In one brand of e-cigarettes, the researchers discovered 10 times the amount of formaldehyde when compared to tobacco cigarettes. Higher carcinogen amounts were detected when the e-cigs’ vaporizers got overheated, the authors said.

However, they also noted that the actual levels of formaldehyde varied throughout the course of their analysis of 10 different e-cig brands. Formaldehyde is found in embalming fluid, and also in building materials for homes and in the environment.

Although electronic cigarettes were invented in the 1960s, they didn’t become popular until about 10 years ago, with usage increasing steadily over the past decade. Today, the e-cig industry has become a multibillion dollar enterprise, with an estimated 2.5 million users worldwide and more brand names each year.

Proponents of e-cigs were skeptical about the study’s results. A spokesperson for the Ecigarette Research Advocates Group, Dr. Farsalinos, pointed out that the results were related to the levels tested in just one e-cig model.

On average, said Dr. Farsalinos, the e-cigs actually contained approximately 50 times less formaldehyde than tobacco cigarettes.

Overall, said the advocacy group, the resulting “media frenzy” caused by the study was “completely inappropriate.” They plan to begin examining the data on their own, taking into consideration puff patterns and more “realistic conditions.”