Twista Lime, Kauai Kolada, Caribbean Chill, Mintrigue. Exotic cigarette flavors like those were banned in 2009 out of concern they might tempt young people.

But the flavors tobacco companies once sold look like plain vanilla compared with the flavor buffet now on offer — legally — by the fast-growing electronic cigarette industry.

News on Tuesday that Reynolds American had agreed to buy Lorillard, uniting two of the nation’s biggest tobacco companies, highlighted how important e-cigarettes have become to the declining tobacco industry. Both Reynolds and Lorillard have pushed hard into e-cigarettes, which offer a new way of delivering a puff of nicotine.

For now, those companies’ flavors are relatively modest, although they may feel pressure to expand into the explosion of competition for the consumer palate, with e-cigarette flavors ranging from banana cream pie to cotton candy.

Across the e-cigarette industry, more than 7,000 flavors are available and, by one estimate, nearly 250 more are being introduced every month. The array of tastes goes far beyond anything cigarette companies ever tried.

Flavors have become central to the conversation because e-cigarette makers say the rainbow of tastes differentiates their products from deadly cigarettes.

But the claim that e-cigarette flavors won’t attract children has prompted an outcry from some policymakers, who say consumers have been down this road with tobacco. Federal health authorities have outlawed most cigarette flavorings except menthol, arguing that they lure the young into nicotine addiction. While the Food and Drug Administration has proposed regulations for e-cigarettes, it has not limited marketing or flavors, which the agency is studying.

At a Senate committee hearing in late June, lawmakers denounced manufacturers for marketing practices that they said appealed to children, including the embrace of flavors that are forbidden in ordinary cigarettes.

"I’m ashamed of you," Sen. Jay Rockefeller, D-W.Va., told several executives. "You’re what’s wrong with this country."

Jason Healy, the president of Blu eCigs, told the Senate Committee on Commerce, Science and Transportation that the average age of people using cherry flavored e-cigarettes, for example, was 40.

Such flavors "decrease the ability or possibility of adult users who use e-cigs switching back" to cigarettes, he said.

Blu eCigs, a Lorillard subsidiary, is being sold to the British company Imperial as part of the deal announced Tuesday. Lorillard and Reynolds said they would focus their e-cigarette efforts on Reynolds’ product Vuse, which in June was introduced in 15,000 stores nationwide.

Vuse has only two flavors, original cigarette flavor and menthol, but the market is changing quickly as evidenced by the experience of other leading e-cigarette companies. Most notable is the experience of NJOY, which has turned to flavors to help stanch plummeting market share.

Ten months ago, NJOY’s chief executive, Craig Weiss, said in an interview that other manufacturers used flavorings "to attract children." NJOY, he said then, was avoiding candy- and fruit-like flavorings, in part because "they drive regulators crazy."

NJOY’s investors include Sean Parker, the Napster co-founder and former president of Facebook, and Bruno Mars, the pop star.

But NJOY’s share of the convenience store market has gone into free fall, dropping more than half in the past year to less than 10 percent, according to Wells Fargo Securities. Consumer surveys suggest that most people who use e-cigarettes — including those who have smoked — tend to prefer flavors other than tobacco. In the next few weeks, NJOY plans to expand into flavors like "Butter Crumble" and "Black and Blue Berry." Weiss said in an interview that the company had little choice after focus groups showed that flavors were "critical."

"Flavor is essential to vapers’ satisfaction," Weiss said.

Some in public health circles see the debate over flavorings as a sideshow. The central question, they say, is whether e-cigarettes are effective tools to get people to stop smoking tobacco. Others say the issue of flavors crystallizes the debate about the risks and benefits of these products, which many consider far safer than conventional cigarettes. At the same time, there is widespread concern that use of e-cigarettes will renormalize the act of smoking and invite in a new generation of participants, particularly through the lure of flavors.

"It defies logic to think that such flavors would not make e-cigarette use more appealing and even normal for children," said James Pankow, a chemistry professor at Portland State University in Oregon, who has studied cancer risk from cigarettes.

Weiss of NJOY, hoping to address personal concerns about flavors, funded a study this year to see whether the company’s new flavors would appeal to young nonsmokers. The study, an online survey conducted by Saul Shiffman, a pharmaceutical industry consultant and psychology professor at the University of Pittsburgh, found that young people were not particularly attracted to the flavors. Flavors did make e-cigarettes more attractive to adult smokers, Shiffman concluded.

About a year ago, NJOY, based in Scottsdale, Arizona, named to its board Dr. Richard H. Carmona, the former surgeon general who had been an ardent foe of tobacco companies. Before joining the NJOY board, Carmona said, he asked the company about the use of flavors and was told it "was not on the table at that time."

Carmona, who also works at a nonprofit health organization, the Canyon Ranch Institute, said that NJOY’s research was a good start but that it was critical that independent researchers validate the findings. Like Weiss, Carmona said he was willing to take the chance and go forward, given that e-cigarettes have the potential to get people to stop smoking conventional cigarettes.

"Research like that could take months or years," Carmona said. "So we go with a theory. We go with a hypothesis. It’s no different than any other market."