“This effect is consistent with e-cigarette access reducing smoking among minors. Banning e-cigarette sales to minors counteracts 70 percent of the downward pre-trend in teen cigarette smoking in the states that implemented such bans.”

Friedman said her findings “will prove surprising for many. Policy discussions to date have not considered that banning e-cigarette sales to minors might increase teen smoking.”

“Assuming that e-cigarettes are indeed less risky to one’s health than traditional cigarettes, as suggested by existing evidence on the subject, this result calls such bans into question.”

Friedman recommends as a potential “middle ground” banning e-cigs and vaporizers for those under age 16, “as initiation of regular smoking first spikes at (that) age.”

States impose bans

For the study period of 2009-13, 24 states had banned the sale of e-cigs and vaporizers to those under 18. An additional 16 states have passed a ban since Jan. 1, 2014.

The Food and Drug Administration recommends a federal ban. Friedman wrote that “a FDA decision not to ban e-cigarette sales to minors, after having announced this intention, could be seen as sanctioning teen vaping, introducing distinct costs not addressed here.”