IQOS is not
an e-cigarette. IQOS heats real tobacco. It does not
vaporize a liquid solution containing nicotine. IQOS is used with HeatSticks which contain naturally present nicotine, whereas in e-cigarettes, nicotine derived from tobacco is added to the liquid.
The U.S FDA has authorized the sale of IQOS in the U.S as "appropriate for public health". FDA press release here