(Reuters) – Several deaths and potentially hundreds of illnesses tied to e-cigarettes, which allow users to inhale nicotine vapor, often flavored, without smoking, have been reported by the U.S. public health agency.

Lawsuits on behalf of young consumers have targeted leading e-cigarette maker Juul Labs Inc. Altria, which holds a stake in Juul, said the number of cases pending against the e-cigarette maker has surged by more than 80% since October.

Several states have instituted partial or total bans on vaping devices, and retailers and industry groups have challenged those bans in courts.

The following is a summary of how the litigation is playing out across the United States:

* Young adult Juul users and parents of teenage users have filed dozens of lawsuits over vaping-related injuries, including both individual lawsuits and class actions. The lawsuits target Juul, which markets a nicotine-vaping device and controls about 75% of the e-cigarette market. Some have also named Marlboro maker Altria Group Inc, which has a minority stake in Juul, as a defendant.

* Most of the lawsuits say that users became addicted to Juul, but at least two go further. A Connecticut man said in a lawsuit filed in California state court that he suffered a massive, debilitating stroke as a result of Juul use, while the parents of a teenage girl said in a proposed class action in Florida federal court that their daughter has suffered seizures linked to the device.

* One set of legal claims in the cases focuses on fraudulent marketing. In these claims, plaintiffs accuse Juul of claiming its e-cigarettes are meant to help adults stop smoking cigarettes, while marketing them to minors and young adults who have never used nicotine. They also say Juul has claimed its products are a safe alternative to cigarettes, when in fact they can deliver higher doses of nicotine.

* Another set of claims focuses on product liability, saying that Juul’s products are defectively designed because they are inherently dangerous, and that Juul failed to warn about the danger or both.

* Juul said in a statement last year that its products are meant as a less dangerous alternative for adults who already smoke. “We have never marketed to youth and do not want any non-nicotine users to try our products,” the company said.

* Altria has said that the conduct alleged in the lawsuits occurred before it acquired its financial stake in Juul. “Our minority stake in Juul provides no basis for liability against Altria,” it said in a statement.

* More lawsuits are expected. Joseph VanZandt, a lawyer with the firm of Beasley Allen, said his firm has been hired by more than 200 clients for vaping-related claims, of whom at least eight have already filed lawsuits. “We fully expect that there will be hundreds if not thousands of individual cases filed,” he told Reuters earlier this month.

* Lawsuits filed in federal court are likely to be consolidated in so-called multidistrict litigation before a federal judge. Juul has moved to consolidate the lawsuits in the Northern District of California, which includes San Francisco. A federal judicial panel in Los Angeles is scheduled to hear arguments on that motion Thursday. Separately, a motion has been filed in a Los Angeles state court to consolidate the California state court cases there.

* North Carolina Attorney General Josh Stein in May sued Juul and has asked a state court to limit the flavors of Juul e-cigarettes sold in North Carolina.

* Other state attorneys general, along with the U.S. Federal Trade Commission, are investigating Juul’s marketing practices. Some states, including New York, Michigan and Rhode Island, have moved to restrict the sale of flavored e-cigarettes; Massachusetts has gone further, instituting a four-month ban on all vaping products.

* These regulations have faced challenges from e-cigarette retailers and industry groups. On Friday, a New York judge blocked a state ban on most flavored e-cigarettes from taking effect after an industry group sued to challenge it, while a Massachusetts judge upheld that state’s ban. A lawsuit by retailers in Michigan challenging that state’s restriction is pending in a state court there.

(Compiled by Brendan Pierson in New York and Nivedita Balu in Bengaluru; Editing by Grant McCool and Sriraj Kalluvila)