When heated to temperatures below the onset of combustion, the tobacco undergoes a number of thermochemical processes, such as drying, evaporation, torrefaction, and low temperature pyrolysis, as shown in Fig. 1 . For combustion of the tobacco to occur, the temperature needs to exceed around 400 °C/752 °F 1 , and three elements must be present: a fuel to be burned, an oxidant (usually the oxygen in air) to oxidize the fuel, and an ignition source (a flame or spark) to initiate the reaction. Combustion (burning) is an exothermic chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light. 2
In a cigarette, combustion occurs when the tobacco is ignited by a heat source, such as the flame from a match or a lighter. Once lit, a self-sustaining exothermic oxidation reaction is established at the tip of the burning cigarette with the tobacco reaching temperatures above 850 °C/1562 °F) 3. The heat released by the combustion process breaks down tobacco leaf components generating smoke and leaves an ash residue. The cigarette smoke formed contains more than 6,000 chemicals,4 some of which have been classified by public health authorities as likely causes of smoking-related diseases, such as lung cancer, heart disease and emphysema.
The IQOS tobacco heating system is based on the heat-not-burn concept: heating tobacco without combustion. As depicted in Fig. 2 , IQOS consists of three distinct components that perform different functions: (i) a novel patented tobacco stick containing a specially processed tobacco material made from tobacco powder, water, glycerol, guar gum, and cellulose fibers (ii) a holder into which the tobacco stick is inserted and which heats the tobacco material by means of an electrically controlled heater, and (iii) a charger that is used to recharge the Holder after each use.