They Produce Second-hand Vapor
It's not only smokers who are impacted by the effects of cigarettes; as many as 2.5 million nonsmokers have died from the lethal effects of secondhand smoke between 1964 and 2014 [source: CDC]. Despite the claims they're a safe alternative to regular cigarettes, e-cigarettes may not completely solve the problem of secondhand exposure to nicotine.
Nicotine exposure from e-cigarettes is real, although studies suggest that exposure is far less from e-cig vapors than from the smoke of regular cigarettes. Nicotine emissions are 10 times lower than from burning tobacco, and the secondhand aerosol doesn't contain significant amounts of tobacco-specific toxins (carbon monoxide or other toxic volatile organic compounds) [source: Czogala].