U.S. Rep. Diana DeGette on Wednesday slammed the chiefs of five e-cigarette companies over their role in enabling an estimated 5 million youths — 28% of all high school students — to vape in the past year.

“E-cigarette manufacturers have been negligent at best or intentional at worst in attracting young people to their options,” DeGette said at a hearing of the House Subcommittee on Oversight and Investigations, which she chairs. She added that companies used slick marketing campaigns and flavors to “lure” young people.

The stated purpose of the hearing was to explore the role of e-cigarette manufacturers in the marketing and use of vaping products, as well as the health implications. Earlier in the week, DeGette held a discussion with six students at South High School in Denver, which she referenced in the hearing.

“The e-cigarette industry has essentially been allowed to conduct a public health experience in real time without knowing what the consequences of these products would be,” she added. The U.S. Food and Drug Administration has not expressly permitted e-cigarettes, choosing instead to focus its enforcement on sales and marketing practices.

U.S. Rep. Frank Pallone, D-N.J., warned that if left unchecked, vaping products could lead youth consumers into addiction like the cigarette companies have allowed in decades past.

“It’s chilling to sit and watch as we are seeing history repeat itself,” he said. “We’ve been here before as the tobacco industry admitted to misleading millions of users on the safety of tobacco products. And we can’t sit idly by as it happens again.”

K.C. Crosthwaite, the CEO of JUUL Labs — which holds an estimated 75% of e-cigarette market share — struck a contrite tone. “At JUUL Labs, our thousands of U.S. employees are committed to helping adult smokers transition away from combustible cigarettes,” he said. “Over the past few years, trust in our company and category has eroded. We are committed to taking concrete action to re-earn that trust.”

Ricardo Oberlander, the president and CEO of Reynolds American Inc., noted that research has shown that 95% of users for Vuse, the company’s vaping product line, are over age 25.

“Though hollow as it may sound,” assured Ryan Nivakoff, the CEO of NJOY LLC, “this industry has the greatest incentive, both moral and economic, to ensure that youth use is eliminated.” Otherwise, he added, the “life changing” vaping technology may be regulated out of existence, to no benefit of adults trying to quit smoking.

Antoine Blonde, president of Fontem U.S., deflected on his company’s responsibility for youth vaping, saying that “Fontem’s products have not been found by the U.S. Centers for Disease Control to be involved in any of the incidents of respiratory illness it has investigated. Vitamin E acetate is not and has never been an ingredient in our product.”

He referred to the additive that the CDC last year found as a likely contributor to hospitalizations for lung illness.

Jerry Loftin, president Logic Technology Development, LLC, took a swipe at his fellow witnesses by saying, “Other companies have caused tremendous damage to the reputation of this category while putting children in harm’s way.”

In her questioning, DeGette asked the representatives if nicotine was addictive. They answered in the affirmative.

“Isn’t it true that using the products of your companies could lead to nicotine addictions?” she continued. Yes, they admitted.

“Would you agree that nicotine can cause respiratory health issues, heart rate and brain development issues?”

“Tobacco products can cause harm,” Oberlander stated.

“Could they cause the harms I just talked about?” DeGette cut in.

“I’m not familiar with the studies,” Oberlander demurred.

“I’m not in a position to corroborate,” Nivakoff added, when asked the same question. DeGette appeared frustrated with their responses.

“I find it fascinating that no one really wants to talk about what that harm is,” she said. “The medical studies show that [nicotine] can cause respiratory health problems, blood pressure, heart rate problems, and brain development problems in young people. Do you think it can cause any of those harms?”

“I have no reason to doubt those studies, but I’m not aware of them,” Blonde allowed.

The CEOs maintained that vaping was preferable for adults to quit smoking combustible cigarettes, which the CDC has identified as the leading cause of preventable death and disease. However, a study published in 2012 found that nicotine exposure for adolescents “may be harmful, since it may derange the normal course of brain maturation and have lasting consequences for cognitive ability, mental health, and even personality.”

DeGette placed the blame for youth nicotine addiction squarely on the e-cigarette companies, saying, “The industry caused this mess and the industry needs to be responsible for cleaning it up.”