Heated tobacco products (HTPs) are tobacco products that produce aerosols containing nicotine and other chemicals which are inhaled by users through the mouth [1
]. In order to produce the nicotine-infused vapor, HTPs heat tobacco up to 350 °C (lower than the 700 °C reached with conventional cigarettes) using battery-powered heating systems [2
]. Different HTP devices use different heating sources, including electronic energy via battery. The enclosed heating system can be an external heat source to aerosolize nicotine from specially designed cigarettes (e.g., IQOS and glo), or a heated sealed chamber to aerosolize nicotine directly from tobacco leaf (e.g., ploomTECH) [3
More recently, HTPs have been marketed and promoted by the major tobacco companies as safer alternatives to combustible cigarettes [4
]. The use of heated tobacco products (HTPs) has increased rapidly over the last few years in Japan [5
]. In 2018, the overall prevalence of monthly HTP use was 2.7% (1.7% daily use) [3
]. Virtually all HTP users were current cigarette smokers (67.8%) or former smokers (25.0%), and only 1.0% were never smokers [5
]. Many HTPs users (50.5% of HTP users) who switch from conventional cigarettes to HTPs do so to avoid exposing bystanders to second-hand tobacco smoke [6
]. Major tobacco companies advertise that HTPs do not generate side-stream smoke or pollute indoor air quality [7
]. In contrast, the World Health Organization (WHO) recommends that HTPs should be subject to the same policy and regulatory measures as all other tobacco products, in line with the WHO Framework Convention on Tobacco Control (WHO FCTC) [1
The revised Health Promotion Act is planned for enactment before the Tokyo 2020 Olympic and Paralympic Games to protect against exposure to second-hand tobacco smoke. As stated in Article 8 of the WHO Framework Convention on Tobacco Control (WHO FCTC), legislation for indoor smoking bans relies on sufficient and unequivocal scientific evidence that exposure to tobacco smoke causes death, disease, and disability. Since the evidence available to date does not convincingly demonstrate that the available HTPs will simply replace conventional cigarettes among current smokers without attracting youths, or even that these products will substantially reduce health risks among users [2
], it is regrettably too early to provide a clear answer on the long-term impact of exposure to the second-hand aerosol of heated tobacco products (HTPs) [1
]. Scientific evidence has not unequivocally established that exposure to aerosol from HTPs causes death, disease, and disability. So, under the revised act, HTPs are treated differently than cigarettes and are positioned as transitional measure until associations with morbidity or mortality are epidemiologically proven [11
]. Some people have argued that HTPs should be regulated in the same way as cigarettes, in accordance with the precautionary principle [12
], while others hold that they should remain unregulated unless there is a legal basis for doing so.
Philip Morris International (PMI) studied and reported the impact of IQOS on indoor air quality, evaluated in an environmentally controlled room using ventilation conditions recommended for simulating “office”, “residential”, and “hospitality” environments [13
]. As industry results, however, these need to be validated through independent study, using a more appropriate evaluation reflecting actual conditions in Japanese restaurant and bar environments. Further, the results should be compared among three different HTPs sold in Japan, not just IQOS, under the same conditions.
Here, therefore, we conducted a pilot exposure assessment with some risk characterization of nicotine and particulate matter (PM) from HTPs under two different conditions. First, we investigated the legitimacy of health concerns under conditions which aimed to replicate use in a small indoor environment. Second, we measured the impact of using these HTPs on indoor air quality under usual indoor environmental test conditions.
According to a previously published paper that examined chemical concentrations in mainstream smoke, while some HTPs contain nicotine at similarly high concentrations to cigarettes, levels of carcinogens are generally low [23
]. Propylene glycol and glycerol are the most common components of PM produced by HTPs [23
]. Nicotine were detected and assessed from second-hand aerosol in the air, as well as when using electronic cigarettes [25
]. Nicotine concentrations in the shower cubicle test were at least one order of magnitude greater than the tolerable concentration without health concerns of 3.0 μg/m3
with use of any of the three types of HTP, namely ploomTECH, glo, and IQOS, althoughlevels were orders of magnitude lower than those with the cigarette. Many bars and pubs are of very small size and lack adequate ventilation, and patrons and staff often find themselves seated or standing close to each other. The area modeled in our shower cubicle of 0.64 square meters per person appears reasonable. The partially revised Health Promotion Act provides for transitional measures for HTP use under which the long-term health effects of second-hand HTP aerosol have yet to be scientifically proven [11
]. Nevertheless, HTPs are included in regulations and their use will be permitted only in designated rooms that meet specified technical requirements. The results of this study are not a legislative basis for the law, but support the inclusion of HTPs within a regulatory framework for indoor use to protect nonsmokers from exposure to HTP aerosol, particularly with regard to the protection of people who are generally sensitive, such as patients with cancer and pulmonary or cardiovascular disease, and small children.
In contrast, nicotine concentrations in the test room remained below 3.0 μg/m3
for all HTPs tested, indicating that nicotine is of no concern with the use of these products. Nicotine dependence occurs as three types: physical dependence, habit dependence, and psychological dependence [27
]. In this study, assuming physical dependence, normalization was performed against the amount of nicotine in mainstream aerosol/smoke. The inhalation volume of users would be accordingly higher for products with less nicotine in mainstream aerosol/smoke. Nevertheless, for all three HTPs, the nicotine concentration in the room was significantly less than that with cigarettes, and did not exceed the tolerable concentration without health concern level of 3.0 μg/m3
at any time. For the other two types of dependence, it is not necessary to normalize against the amount of nicotine, and assuming that these types will be used, nicotine concentration in the room should be further lowered. It should be remembered that levels depend on the strength of ventilation and the structure of the room. Moreover, our testing was conducted with the room ventilator stopped throughout the test, whereas the technical requirement for designated heated tobacco smoking rooms under the law requires ventilation [8
]. Nicotine concentration in ventilated rooms would likely decrease further.
Tests conducted by PMI reported nicotine concentrations of 1.10, 1.81, and 0.66 μg/m3
, respectively, in a room of 24.1 m2
in size. Indoor constituents were measured during IQOS sessions under conditions that simulated office, residential, and hospitality environments. When conventional cigarettes were used, namely Marlboro Gold, values were 34.7, 29.1, and 34.6 μg/m3
, respectively [13
]. In our present study, nicotine concentrations did not differ significantly from those in the PMI study of IQOS, although there were some differences in condition settings, such as the presence/absence of ventilation. Specifically, PMI stated “Using THS2.2 (i.e., IQOS) indoors does not have a negative impact on air quality”, “The European Agency for Safety and Health at Work has established a exposure limit at 500 μg/m3
(8 h) to be compared to a maximum median value of 1.8 μg/m3
for THS 2.2 (275-fold lower)” [28
]. For our present study, however, these statements would not necessarily be appropriate. Using HTPs indoor also has negative impacts on air quality. Moreover, while nicotine concentrations in the air are below the tolerable level of 3 μg/m3
under controlled scenarios in the normal range, these could be easily exceeded in some conditions, as shown by the shower cubicle test.
The indoor PM2.5 concentration of about 300 to 500 μg/m3
when using IQOS or glo in the shower cubicle is in the air quality index (AQI) category of “hazardous” (Figure 1
], a level that exceeds the average daily concentration of 350 μg/m3
in just 2 h indoors. In contrast, when IQOS and ploomTECH were used in the 25 m2
room, levels were below the standard value of 15 μg/m3
per year and 35 μg/m3
per day, as specified by the US Environmental Protection Agency and Ministry of the Environment, Japan [29
concentration when using glo was slightly high, albeit still much lower than the hundreds of micrograms seen when cigarettes are smoked. Some measurements exceeded 100 g/m3
, but it is unclear whether this would exceed the standard value of 35 μg/m3
for 24 h considering the amount of time spent in the room per day. As PM2.5
concentration with glo tended to differ from those with IQOS and ploomTECH, research into particulate exposure with HTPs should include the physical properties of fine particles.
Under the revised Health Promotion Act, the handling of HTPs is a transitional measure, namely a provisional measure until a clear answer on the long-term health impact of usage or exposure is obtained [11
]. This study did not negate the registration of HTPs under the revised Act. Research into the adverse health effects of HTP use and second-hand aerosol is a public health duty, and the law should be reviewed to take account of future research. Under the revised Health Promotion Act, the regulation of HTPs is a transitional measure. Further revisions of this transitional measure will require additional research on indoor air quality.
Several limitations of our study warrant mention. First, the limited time between the drafting of the bill and its submission to the National Diet, as well as resource constraints, did not allow a sufficient number of tests for statistical analysis of the measurement results. There was not enough time to submit the bill to parliament in order to meet the parliamentary debate schedule. Significant resource constraints were present in terms of testing sites, personnel, and funding, among others. While this is a small-scale test of a hypothesis to obtain a primary outcome, this might raise concerns about the robustness of the methodology. Second, the NOAEL of nicotine was derived from testing in rat models using exposure to inhalation of nicotine [14
], which might not be extrapolatable to human conditions. Differences in model animal species and the ongoing accumulation of findings from chronic toxicity studies may change assumptions about the tolerable concentration without health concerns. Third, we only investigated two limited cases, and the failure to account for a range of scenarios and variables, including ventilation rate, room conditions and number of smokers, means that our results cannot be generalized. The government study group’s report stipulated only the size of the floor area, as determined from an assumed number of restaurant seats [22
]. In our present test, we used a testing room with a height of 2.56 m. Other venues have lower ceiling heights, and concentrations would accordingly be expected to be higher. Actual customer behavior and the manner of smoking of individual smokers or users will vary, requiring evaluation in actual restaurants and bars in future studies. In addition, the room test was conducted under non-ventilated conditions. Measurement under regular ventilation conditions was not possible due to constraints of the test facility. After the legislation on HTPs is enacted, indoor air quality should be measured and evaluated in newly emerging designated HTP smoking rooms in various real-world restaurants, cafés, and other environments. Results on differences in air quality, for example nicotine and PM concentrations, depending on conditions among facilities of different types, room sizes, and ventilation systems could provide insight into how the revised Act’s transitional measures should be reviewed. Fourth, various types and flavors of HTP have been recently put on the market, but this study does not cover them. In addition, counterfeit devices having different operating temperatures from genuine products have also emerged. Evaluation testing of these is an issue for the future. The limitations presented by these test conditions are mitigated by the fact that concerns about second-hand aerosol arise even with HTPs. Finally, and most significantly among limitations, this study did not evaluate other chemicals, such as volatile organic carbons (VOCs), polynuclear aromatic hydrocarbons (PAHs), tobacco-specific nitrosamines (TSNAs), and aldehydes [23
]. Exposure risk assessment of indoor air environments should assess not only nicotine and particles, but also other toxic chemicals, especially carcinogens [23
]. Since existing thresholds do not consider carcinogenicity through injury of genes and mutagenicity etc. through activity on germ cells, one method of risk assessment used in such cases adopts the amount which causes carcinogenesis at a probability of 1/100,000 as a virtually safe dose (VSD) [16
]. Multiple options are proposed, and this topic remains controversial.