The growing popularity of e-cigarettes among smokers has led to increased availability with a number of new manufacturers entering the market every year. Also, these devices are being used in spaces where smoking has been banned, leading to increased indoor air pollution despite reductions in building air exchange rates. The few extant studies of e-cigarette emissions, although limited in the number of products tested, show that these devices pollute indoor air. Nevertheless, they are being promoted as "emitting only harmless water vapor," when studies show the emission of polluting VOCs, as well as heavy metals and fine and ultrafine particles. There is little or no quality control in, or government oversight of the manufacture of E-liquids. If dozens of so-called "vapers" begin to frequent bars, restaurants, discos, offices, and are permitted to these fog the air on aircraft, decades of progress in cleaning up indoor air in workplaces and public access buildings is on the threshold of reversal. This is a very dangerous development.