Findings from a comprehensive survey of electronic cigarettes, or e-cigarettes–and the liquids intended for use with them–marketed online show that the market is rapidly expanding and will likely pose challenges for regulatory agencies that are still determining how best to proceed. Researchers at the University of California, San Diego School of Medicine reported the results of the survey in the July supplement to the journal Tobacco Control.

“The product has caught on fire,” said Shu-Hong Zhu, a public health researcher at the University of California-San Diego who helped lead the research.

The team found that from 2012 to 2014, an average of 10 new e-cigarette brands entered the online marketplace per month. Today, there are a little over 466 e-cigarette brands available for purchase via the internet, and more than 7,700 flavors of the liquid mixture used in the devices are available to customers. Among the available flavors are candy mimics such as gummy bear and marshmallow, flavors some experts worry are too alluring to children. In contrast, traditional tobacco cigarettes sold in the U.S. come in two flavors, plain and menthol.

Another trend that Zhu and colleagues found is a move away from the look of traditional cigarettes. When e-cigarettes first became available, they looked like regular cigarettes. Over time, however, the devices have looked less and less like cigarettes and more like pens, flashlights, and other objects not resembling traditional cigarettes at all.

E-cigarettes do not produce smoke. They are battery-powered devices that heat flavored, nicotine-rich liquids to form vapors that the user inhales, much like cigarette smoke but without the toxic ingredients of tobacco smoke. The devices generally deliver lower amounts of nicotine per inhalation than do traditional cigarettes.

Health experts debate whether or not the devices are harmful or helpful, and a number of publications have emerged recently supporting and attacking the idea that they may be effective smoking-cessation aids.

“Some consider them promising products to help smokers quit traditional cigarettes, while others believe they will re-normalize smoking, which will keep more people smoking,” Zhu said.