Surgeon General Vivek Murthy told The Washington Post on Thursday that young people should not use any products containing nicotine, including e-cigarettes. “The key bottom line here is that the science tells us the use of nicotine-containing products by youth, including e-cigarettes, is unsafe,” he said.

In recent years, the use of e-cigarettes among teens has jumped dramatically, with more high school students using them than regular cigarettes. A study by the Centers for Disease Control and Prevention found that 16% of high school students used e-cigarettes in 2015, up from just 1.5% in 2011, according to Murthy’s full report.

The report cites possible addiction and the potential for long-term harm to brain development and respiratory health as key dangers for youths. It notes that human brain development continues until a person is roughly 25 years old.

New regulations put in place by the Food and Drug Administration over the summer already ban the sale of e-cigarettes and other tobacco products to minors (anyone under the age of 18). But, as is the case with cigarettes, that hasn’t stopped underage teens from getting their hands on them.

Industry representatives have argued that the increased regulation around e-cigarettes will raise manufacturers’ costs and put smaller companies in the industry out of business. The Surgeon General’s new warning isn’t likely to help, either.

Still, Reynolds American, the U.S. tobacco giant behind the leading e-cigarette VUSE, agreed with the Surgeon General’s assessment that minors should not use e-cigarettes. Jacob McConnico, a spokesman for Reynolds American, told Fortune in a statement that while the company would not comment on details of the report, “we do agree with the Surgeon General that minors should never use e-cigarettes or any other tobacco product.”

“Additionally, adults who do not use tobacco products or who have quit using tobacco should not start using e-cigarettes or any other tobacco products,” he said.

Tyler Goldman—CEO of PAX Labs, which makes the popular PAX vaporizers and JUUL e-cigarettes—was also quick to agree with the new warning. “JUUL should not be used by those under the legal age, nor should any nicotine products, as stated by the U.S. Surgeon General,” Goldman told Fortune. “PAX Labs discourages any underage consumers from using its products and strongly supports efforts to prohibit and prevent underage use of all nicotine products.”

Goldman argues that his company’s e-cigarettes are intended as a tobacco alternative for the 36.5 million adult tobacco smokers in the U.S. While the exact long-term health effects of e-cigarettes are still up for debate, there is research that suggests the products are a relatively healthy alternative to traditional tobacco smoking. Earlier this year, the U.K.’s Royal College of Physicians argued that e-cigarettes are a helpful, and significantly less harmful, alternative to other methods of quitting smoking.

UPDATE: VMR Products, the Miami-based company that makes V2 e-cigarettes and vaporizers, also sent Fortune a statement in response to the Surgeon General’s warning. The statement read, in part: “The electronic vapor industry is committed to keeping vaporizers out of the hands of underage consumers. These devices are not and have never been intended for anyone under the age of 18.” The company also argued that it is important to recognize the importance of what it calls “the benefits of electronic vaporizers for adult smokers” and cited the study from the Royal College of Physicians.

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