Teens who vape may not realize how much nicotine they are consuming — if they are aware they're consuming it at all — when using e-cigarettes, a new study released this week claimed.

The study, published in the journal Pediatrics on Monday, surveyed more than 500 participants aged 12 to 21 about their usage of tobacco, e-cigarettes, and marijuana. The study’s participants also gave a urine sample, which researchers tested for different biomarkers such as cotinine, which forms in the body after using nicotine products, per the Centers for Disease Control and Prevention (CDC).

By the end, researchers determined 40 percent of participants who said they used products that did not contain nicotine had “significant levels of nicotine biomarkers in their blood,” according to Healthline.

Additionally, the researchers found those who reported using Juul-like devices had "comparable or even higher [levels of cotinine] to what you see with kids who smoke cigarettes,” Rachel Boykan, the study’s lead author, told USA Today.

"We’re talking about kids getting addicted to nicotine and using these things because they perceive them as being safer than cigarettes, but these are kids that would not have been smoking in the first place," she added.

E-cigarettes are battery-powered devices that in most cases heat a flavored nicotine solution, turning it into a vapor that can be inhaled – a practice known as vaping. The e-cigarettes differ in how much nicotine they deliver.

The study echoes 2016 statistics provided by the National Institute on Drug Abuse. At the time, the federal institute reported 66 percent of teens surveyed thought “just flavoring” was in their e-cig, while nearly 14 percent said they were unsure what was in the device. Just 13.2 percent said nicotine.

“The study demonstrates that nicotine is often an ingredient found in vape products, even though the user may not be aware of it,” added Patricia Folan, the director of the Center for Tobacco Control at Northwell Health in Long Island, New York, who was not involved in the study, to Healthline.

Health officials often warn vaping is not good for your health.

U.S. health officials are now investigating whether electronic cigarettes may trigger seizures in some people who use nicotine-vaping devices.

Additionally, there is a nationwide push to fight underage use of e-cigarettes, which have surged in popularity among high school and middle school students, particularly. The FDA recently outlined new restrictions on retail and online sales of most flavored e-cigarettes. Meanwhile, local and state officials are considering age restrictions, taxes and flavor bans to keep the products away from teenagers.

Fox News' Dr. Marc Siegel and The Associated Press contributed to this report.