With the rising popularity of e-cigarettes and vaping, especially among teenagers, scientists are calling for more research into the flavored liquids used to vape. A new study published in Environmental Science & Technology has called for more thorough research into the health effects of inhaling vapors after they discovered hazardous chemicals in e-liquids.

The findings revealed that the amount of aldehydes produced by flavored e-cigarette liquids exceeded the American Conference of Governmental Industrial Hygienists Threshold Limit Values (TLVs) for hazardous chemical exposure, according to a press release from Desert Research Institute.

Toxic aldehydes, such as formaldehyde, are created by the chemical breakdown of flavored e-liquid caused by the device’s rapid heating process, the release noted.

Researchers used a controlled sampling system to simulate common vaping conditions, according to a statement. Vapors similar to those from e-cigarettes were produced from each device by a four-second, 40-ml controlled puff, with 30-second resting periods between puffs. The research team tested five flavored e-liquids in each device, as well as two unflavored e-liquids.

“One puff of any of the flavored e-liquids that we tested exposes the smoker to unacceptably dangerous levels of these aldehydes, most of which originates from thermal decomposition of the flavoring compounds,” researcher Andrey Khylstov said in a press release from DRI. “These results demonstrate the need for further, thorough investigations of the effects of flavoring additives on the formation of aldehydes and other toxic compounds in e-cigarette vapors.”

This isn’t a totally new revelation; back in January 2015, a peer-reviewed letter from the New England Journal of Medicine revealed that the vapors e-cigarette users inhale contain multiple forms of formaldehyde.

Additionally, a 2014 study found that using e-cigarettes has the same short-term effects on the lungs as smoking conventional tobacco cigarettes, according to Science News.

Source: Khylstov A, Samborova V. Flavoring Compounds Dominate Toxic Aldehyde Production during E-Cigarette Vaping. Environmental Science & Technology. 2016.

Read more:

Smoking vs. Vaping 2016: 4 Facts And Myths About E-Cigarettes And Health

E-Cigarettes’ Effect On The Immune System Could Make Them No Better Than Regular Cigarettes