Fifteen years ago, two Stanford graduate students, Adam Bowen and James Monsees, presented their product design thesis on the “future of smoking.” In a video of the presentation, Bowen and Monsees are heard describing their interest in design for social change and pondering aloud if it was “possible to make a safe cigarette.”

“The industry is ripe for innovation,” said Monsees at the time.

Today, Bowen and Monsees are chief technology officer and chief product officer, respectively, of Juul Labs, a company valued at $38 billion. But instead of being seen as an agent of social change, Juul has increasingly found itself labeled — by politicians, regulators and health experts — as one of the instigators of the teenage vaping epidemic. Vaping has been further scrutinized generally as regulators investigate the role of contaminants or counterfeit substances in hundreds of cases of lung illnesses possibly related to vaping.

Juul, for its part, has maintained its product is intended for adult smokers only.

So how did Juul go from its Silicon Valley roots to being associated with Big Tobacco? Here’s what you need to know.

What is Juul?

Bowen and Monsees’s thesis presentation gave rise to a San Francisco-based company, which introduced its Juul e-cigarette in 2015. Two years later, Juul was spun out into a separate company. Last year, Altria Group, the maker of Marlboro cigarettes, took a 35 percent stake, more than doubling Juul’s valuation to roughly $38 billion.

Juul’s slim device was envisioned during that thesis presentation to deliver nicotine and flavor to the smoker through water vapor, minimizing combustion. To limit the “offensiveness” of traditional smoking for both the smoker and those around them, the device would deliver the vapor in flavors such as peach-strawberry.

Today, Juul dominates the e-cigarette market with its devices, despite challenges from other big companies. In the three years after it launched in 2015, the company captured nearly 70 percent of the e-cigarette market, according to a Wells Fargo analysis of Nielsen sales data.

But the company has drawn scrutiny for marketing practices critics say were aimed at teenagers and potential health problems related to vaping generally.

How does vaping work?

An e-cigarette or similar device heats liquid containing nicotine, flavoring and other chemicals, creating a vapor for inhalation. Juul’s products, and those of many of its competitors, look similar to a USB flash drive.

The process delivers fewer harmful chemicals to smokers’ lungs than conventional cigarettes, according to the Centers for Disease Control and Prevention, though e-cigarettes often contain higher concentrations of nicotine, an addictive chemical. Some people also use vaping devices to inhale THC, the main psychoactive chemical in marijuana.

But it’s still unclear what health complications could be associated with vaping. The number of cases of suspected vaping-related lung illnesses have grown quickly, to 354 potential cases in 29 states. State and federal health authorities are focusing on the role of contaminants or counterfeit substances as a likely cause.

Officials have urged Americans to stop vaping until the officials figure out what’s going on. Juul said it commends the investigation and is monitoring reports of the illnesses.

Why are lawmakers cracking down?

Juul’s devices — as well as those of competitors — are extraordinarily popular with teens. The U.S. Food and Drug Administration found a 75 percent increase in e-cigarette usage among high school students between 2017 and 2018, leading the agency to declare an “epidemic” of teenage vaping. It also cracked down on retailers selling to underage teens.

In June, San Francisco became the first major U.S. city to ban e-cigarette sales, an effort to prevent “another generation of San Francisco children from becoming addicted to nicotine.” The ban goes into effect early next year and applies to both brick-and-mortar stores and products shipped to San Francisco addresses. On Wednesday, Michigan became the first state in the nation to ban flavored e-cigarettes, a step the governor said was needed after the state health department found youth vaping constituted a public health emergency.

As the market leader, Juul has borne the brunt of accusations it has drawn younger users with its sweet-flavored products. Earlier this year, researchers at Stanford’s medical school concluded that “Juul’s advertising imagery in its first 6 months on the market was patently youth oriented,” and that its use of social media platforms and influencers may have targeted the market. At a House subcommittee meeting this summer, lawmakers accused the company of “deploying a sophisticated program” to target children and teenagers at places that included schools and summer camps.

Juul’s response

Juul has vehemently denied the allegations. In a statement, Juul spokesman Ted Kwong said the company has “taken the most aggressive actions of anyone in the industry to combat youth usage.” The company has removed all sweet-flavored Juul pods — excluding tobacco and menthol flavors — from the shelves of traditional retailers such as 7-Eleven and Chevron gas stations, though sweet flavors are still available online through Juul’s e-commerce site. Kwong also says it has strengthened its online age-verification process and shut down its Facebook and Instagram accounts.

Juul said the program referenced by the House subcommittee panel was short-lived and designed to educate young people about the dangers of nicotine addiction. The company says its early marketing campaigns were focused on smokers ages 25 to 34, and that Juul has since switched its tactics to focus exclusively on stories of adult smokers who have switched to their products from combustible cigarettes.

Additionally, Juul is working with retailers to implement strict age-verification standards in which point-of-sale systems would automatically lock when a Juul product is scanned and remain locked until a valid of-age ID is scanned. All Juul retailers must have the new system implemented by May 2021.

What’s next for Juul?

Juul is battling a number of lawsuits and faces increased hurdles to selling its products in the United States. In May, North Carolina Attorney General Joshua Stein filed suit against the company, alleging that Juul caused consumer addiction by “deceptively downplaying the potency and danger of the nicotine,” among other claims.

Juul said it is cooperating with Stein’s office.

Juul is also expanding abroad. This week, its products became available in Belgium. That means Juul’s devices are now available in 18 countries including Canada, Russia and South Korea. Juul’s Kwong said in a statement that the company’s mission “is to improve the lives of the world’s one billion smokers by offering a viable alternative to combustible cigarettes.”

Correction: An earlier version of this article incorrectly identified the thesis title.