Should IQOS Emissions Be Considered as Smoke and Harmful to Health? A Review of the Chemical Evidence

Abstract

The chemical evidence that IQOS emissions fit the definition of both an aerosol and smoke, and that IQOS and potentially other heated tobacco products (HTPs) pose some harmful health threats from the range of compounds released even at somewhat lower concentrations is reviewed. Further, we address the yields of harmful and potentially harmful compounds (HPHCs), including polycyclic aromatic hydrocarbons (PAHs), and the constituents of IQOS emission that are diagnostic of pyrolysis to provide information on the temperatures reached in IQOS tobacco sticks. The HPHCs present in IQOS emissions are the same as in conventional cigarette smoke (CCs), analogous to emissions from earlier generation of HTPs classed as smoke. However, Philip Morris International (PMI) studies have to some degree underestimated IQOS aerosol HPHC yields, which are a factor of between 3.2 and 3.6 higher when expressed on a tobacco rather than an IQOS stick basis compared to the reference 3R4F cigarette. Further, IQOS emissions contain carbon particles, which fit definition of both aerosol and smoke. Continual reheating of deposited tar in the IQOS device will occur with real-life use, likely leading to generation of even higher concentrations of HPHCs and particulate matter. Despite IQOS not exceeding 350 °C, local hot spots could exist, causing formation of species (phenol/cresols, PAHs). It is recommended that the impact of repeated use to determine the levels of black carbon (insoluble organic matter) in the particulate matter, and the extent to which compounds in IQOS emissions are formed by pyrolysis need to be assessed rigorously. To address whether uneven temperature profiles in heat sticks can lead to potential hot spots that could, for example, lead to PAH formation, it is recommended that pyrolysis studies on tobacco and other constituents of HTPs are required in conjunction with more effort on heating tobacco blends under controlled temperature/time conditions.

Figure 1

Internal view of the IQOS holder. (A–C) Clean, unused holder showing heater (blue arrows). (D–F) Used holder that was cleaned after every use; black residue remains on heater (red arrows). (G–I) Used holder that was not cleaned between uses (10 uses). Adapted from an independent study Davis et al. and reproduced with the permission of BMJ Publishing Group, Ltd.

Figure 2

Comparison of IQOS (THS 2.2) aerosol total particulate matter (TPM), tar (NFDPM), and water yields to 3R4F reference cigarette smoke yields generated under HCI regimen. TPM does not include compounds in the gas vapor phase (GVP). However, on an equivalent tobacco basis, the IQOS TPM and NFDPM yields should be multiplied by at least 3.2. Note: 3R4F used for each study is the same sample; any difference in yield reflects experimental error from different experiments. PMI MRTP data are average yields of regular and menthol heatsticks, while Schaller et al. is for FR1 blend.