US Surgeon General Dr. Jerome Adams gives a statement on the use of e-cigarettes by teenagers in Washington,DC on December 18, 2018

The top US doctor on Tuesday called for "aggressive" action against e-cigarette use, which he said has exploded to epidemic proportions among youth and puts their health and brain development at risk.

"We must take aggressive steps to protect our children from these highly potent products that risk exposing a new generation of young people to nicotine," Surgeon General Jerome Adams said in a rare public advisory.

"E-cigarette aerosol is not harmless," he said, noting that "nicotine exposure during adolescence can harm the developing brain -– which continues to develop until about age 25."

It is only the second public advisory by the surgeon general since he took the post 16 months ago.

The last advisory, in April, called for more people to carry the overdose antidote naloxone as the nation grapples with a record number of opioid overdoses.

Vaping has also reached all-time high proportions among American youngsters.

In the past year alone, e-cigarette use increased 78 percent among high school students, one in five of whom now say they vape -- using battery-powered devices to inhale nicotine liquids that are often fruit or candy flavored, and highly addictive.

In all, more than 3.6 million US youth, including one in 20 middle school students, use e-cigarettes.

- Market surge -

The devices first came onto the US market around 2007. Since 2014, they have been the most commonly used tobacco product among American youth.

For adults, research has shown that e-cigarettes have fewer harmful components than regular cigarettes, and may help smokers wean themselves from cigarettes.

With smoking still the leading cause of preventable death in America, cutting out cigarettes remains a worthwhile goal, said Health and Human Services Secretary Alex Azar.

"E-cigarettes could help many American adults end their addiction to traditional cigarettes," he told reporters.

"But we cannot let them ensnare younger Americans into a new addiction."

Just three percent of US adults use e-cigarettes, far fewer than the rate among high schoolers, which tops 20 percent.

Vaping among US 12th graders, those in their final year of high school, doubled in the past year alone.

Azar described the surge as an "unprecedented challenge."

- Steps urged -

Adams said many teenagers think that e-cigarette vapor poses no danger.

"We know that the notion that e-cigarette aerosol is harmless water vapor -– something even my 14-year-old son thought was true -– is a myth," Adams said.

"Although e-cigs generally contain fewer toxicants than combustible tobacco products, they can expose users to harmful chemicals in addition to nicotine," he added.

"Less harm does not mean harmless."

E-cigarettes can make it harder for youngsters to learn and remember and pay attention, as well as putting them at risk of future addiction, according to Adams.

They also contain "harmful substances, including heavy metals, volatile organic compounds, and ultrafine particles that can be inhaled deeply into the lungs," said the advisory.

The surgeon general urged parents, doctors and educators to take a series of steps, including banning indoor vaping, and talking to kids about the dangers of e-cigarettes, mentioning by name the USB drive-shaped products made by JUUL.

"We applaud the advisory by @Surgeon_General to help reverse this dangerous trend," tweeted the American Association for Cancer Research.