Impact of the use of heated tobacco products (HTP) on indoor air quality

: Introduction : Heated tobacco products (HTP) have gained popularity in recent years. However, questions have been raised about the damage they cause to health, especially the impacts resulting from exposure to their emissions. This study aims to evaluate the impact of the use of HTPs indoors on air quality and/or the health of passively exposed people, through a systematic review of original studies. Methods : A bibliographic search was carried out in the Medical Literature Analysis and Retrieval System (MEDLINE), Excerpta Medica Database (EMBASE), Latin American and Caribbean Health Sciences (LILACS) and SCOPUS databases. Results : 21 studies were selected and included in this review. The results indicate that heated tobacco products are a source of environmental pollution due to the emission of particulate matter. The stages of selection, data extraction and risk of bias assessment of the studies were performed in pairs, independently, and disagreements were resolved by consensus. Conclusion : Heated tobacco products produce emissions that can expose people to toxic substances emitted indoors, just like other tobacco products.


Introduction
Smoking is a chronic and epidemic disease caused by nicotine addiction present in tobacco products.It is stated in the 11th International Classification of Diseases (ICD-11) for mortality and morbidity statistics, in the group "mental, behavioral or neurodevelopmental disorders", in "disorders caused by nicotine use" (WHO, 2022).
The World Health Organization (WHO) states that tobacco kills more than 8 million people per year.More than 7 million of these deaths result from direct use of the product, while close to 1.2 thousand are the result of non-smokers exposed to secondhand smoke.WHO affirms, furthermore, that about 80% of the world's two more than one billion smokers live in low-income and medium-income countries, where the weight of tobacco-related illnesses and deaths is higher (WHO, 2019).
In accordance with the Resolution of the Collegiate Directorate (RDC) nº 46/2009, of the Brazilian Health Regulatory Agency (ANVISA), the Electronic Devices to Smoking (EDS) mimic the act of smoking and encompass a series of products with various functionalities, various formats, and flavors, as well as different ways of generating emissions.Considering the function, the content and the emissions, they are smoking products, which may or may not be derived from tobacco (ANVISA, 2009).
EDS can be divided into three groups: products that use a liquid matrix, such as electronic cigarettes; those that use a solid matrix, such as heated tobacco products; and hybrids, that we can use both matrixes.In a short time, new models will emerge, with great technological appeal and modern design, such as fourth-generation electronic cigarettes, which use nicotine cartridges (PODs), such as Juul, and the renaissance of heated tobacco products (HTP), such as IQOS and Glo.Likewise, the design of electronic cigarette atomizing units is in constant evolution (WILLIAMS; TALBOT, 2019;BERTONI;SZKLO, 2021;TOBACCO TACTICS, 2023).
However, this technology is calling attention, especially among young people and never smokers.This fact can be observed in the rapidly increasing prevalence of e-cigarette use in the United States, for example.Scholars have stated that, in 2011, the prevalence of use among high school students was 1.5%, and in 2014 it jumped to 13.4%.Alert remains that, in 2019, the prevalence of conventional cigarettes has surpassed (27.5% versus 5.8%) (BERTONI; SZKLO, 2021).
| Page 3 of 30 Among EDS, HTPs require the use of an electronic device to heat a tobacco rod or capsule to a temperature high enough to generate a nicotine aerosol (mostly) to be inhaled.HTPs systems are fully integrated, so that the heating device and the rods or capsules of each must be used together.Usually, the systems are proprietary for each manufacturer, since the components are not interchangeable.Furthermore, various types of refills are used with additives that facilitate experimentation, thus leaving the products more palatable (GLANTZ, 2018;ACTBr, 2019;STOP, 2022).
By 2021, HTPs will represent 3% of the global market for tobacco products; All in all, we have seen a significant growth in sales in recent years.Regarding the estimated participation in the global HTPs market, Philip Morris International (PMI) has 71.5% of the market with the IQOS brand, followed by British American Tobacco (BAT), with 15.3%, with its Glo brand, and Japan Tobacco International (JTI), with 4.3%, with the Ploom brand.Korean Tobacco & Ginseng (KTG) owns the brand Lil and owns 2.9% of the market (in markets outside of South Korea, this brand is sold under license by PMI).There are still other brands marketed in Europe by Imperial Brands, in Asia by China National Tobacco, such as Pulse and Mok, among others (STOP, 2022).
Still, it should be noted that heated tobacco products are not a novelty.The tobacco industry developed technology for two tobacco products aged in the 1960s, being launched on the market in the late 1980s, but with no commercial return.Likewise, these products, despite having updated their technologies, basically present the same concept of two previously launched products, relaunched as novelty and presenting allegations, for example, of being a "cleaner" tobacco product (ELIAS et al., 2018).
In Italy, the sales of two HTPs jumped from 11 tons per year in 2015, to 519 tons in 2017 (LIU et al., 2018), where the goal of two HTP users (45%) and more than two people interested in products had never smoked traditional cigarettes (LIU et al., 2019).
Studies attest that these products emit particulate matter and dozens of toxic substances.Among the measures indicated by the WHO to reverse the tobacco epidemic, the need to implement tobacco-free environments stands out.This measure contributed to making smokers stop smoking and contributed to avoiding passive exposure to product emissions (WHO, 2023).
In Brazil, the use of EDS in collective indoor environments is banned.On December 14, 2011, Law No. 12,546 was approved, prohibiting smoking indoors throughout the country.The Art. 2 of Law No. 9,294, of July 15, 1996, came into force with the following wording: "It is prohibited to use cigars, cigarettes, pipes or any other smoking product, derived or not from tobacco, in indoor, private or public collective premises."Include as indoor collective environments: public offices, hospitals and health posts, classrooms, libraries, collective work venues and theaters and cinemas (BRASIL, 2011).
Thus, this study aims to analyze the effects of aerosol/vapor/smoke/aerodispersoids from HTP in the indoor quality of air, through a systematic process of review of the scientific literature. 1 Methodology This is a systematic review of literature in the databases Medical Literature Analysis and Retrieval System (MEDLINE), Excerpta Medica Database (EMBASE), Latin American and Caribbean Literature in Health Sciences (LILACS) and Scopus.The structured PECO acronym refers to: P (population): people exposed to HTP aerosol/ smoke in indoor environments; E (exposition): aerosol/smoke emitted by HTPs; C (control or comparer): internal free air of aerosol/smoke of HTPs; O (outcome): internal air pollution and/or impacts on the health of passively exposed people.For each component of the PECO strategy, a set of descriptors and free terms was selected, extracted from two controlled vocabularies Descriptors of Health Sciences (DeCS), Medical Subject Headings (MeSH) and Embase Subject Headings (Emtree).Based on these components, the following research question was presented: what is the impact of the use of HTPs in internal/indoor environments on the quality of the health of passively exposed people?

Development of search strategies
The search strategies were elaborated (Chart 1) on May 10, 2022, correlating search terms for each PECO component, by means of two Boolean operators AND and OR.No data, language and/or study design filters are applied, so as not to limit the results, and all the strategies will follow the recommendations of the Peer Review of Electronic Search Strategies (PRESS).
Physis: Revista de Saúde Coletiva, Rio de Janeiro, v. 33, e33SP103, 2023 | Page 6 of 30 Additionally, the references were consulted in two studies selected for reading the full text, being recovered six references that had not been considered in the initial search.The retrieved references are exported to the EndNote Online reference manager, to exclude duplicates between the databases.After this process, a file was generated, in RIS format, to export and make it possible to select two studies in Rayyan software.

Studies selection
The selection of studies was done independently by two reviewers and occurred in three stages: (1) reading of the title and abstract, to include studies that answered the research question; (2) reading in full two studies selected in the previous phase; (3) analyze the references of the two studies included to capture and include possible studies not recovered by searching the databases.Any discrepancies during the stages are resolved by consensus between the reviewers or by reading it by a third reviewer.

Eligibility criteria
As inclusion criteria, the original studies that attend the established PECO are selected.Exclusion criteria were in vitro studies, studies with animals, reviews, abstracts from congresses, editorials, letter to the editor and theoretical essays.

Data extraction
For the analysis and subsequent synthesis of two recovered documents, a data extraction sheet was used, prepared in Microsoft Excel, with the following information: author, year, study title, aim, study destination; description of the place where the experiment was carried out; description of the experiment; waste measures; results; conflict of interest; and source of financing.The plan was reviewed by two reviewers independently and any discrepancies were resolved by consensus.The information collected in this extraction phase is stored in an electronic data bank created in the Microsoft Excel for Windows® version 2019 program.

Classification of electronic cigarettes, heated tobacco and hybrid products
There are different models of electronic smoking devices on the market.To perform an analysis of two studies, it was necessary to differentiate them.The following table presents a summary of the main characteristics of these products.

DEFs
Electronic cigarettes Heated tobacco Hybrid products

Mechanism and components
Device in which a battery heats a liquid solution (e-liquids), with or without nicotine (in different concentrations) and produces an aerosol that the user inhales.Electronic cigarettes usually contain: water, flavoring, nicotine, propylene glycol and glycerin.
Rechargeable electronic warming device that uses processed tobacco sticks (cigarette) or capsules.
In this case, there are two types of devices: those that can use both solid and liquid matrices.
There is even a type of product that uses a stick like those of HTPs along with a chamber with nicotine-free e-liquids to generate vapor similar to electronic cigarettes.

Tobacco
It uses a liquid tobacco extract.
Yes, they heat Tobacco.
Yes.There are hybrid products that may use liquid extracts, tobacco, cannabis, herbs or other plants.

Nicotine
Electronic Nicotine Delivery Systems with and without nicotine.
There are "e-liquids" with or without nicotine.

Yes
There are "e-liquids" that may or may not contain nicotine.
There are products that use tobacco.
Other types of plants can also be used in these products.
It is important to note that, in addition to two common HTPs, there are still other hybrid products.These are models of portable vaporizers for double use.They can vaporize chopped tobacco, dry herbs and even Cannabis, i.e., they can be used by their owners for different purposes.Furthermore, some manufacturers also call for hybrid products, heated tobacco products that present a kind of chamber with propylene glycol or another substance to generate vapor in a similar way to electronic cigarettes.For the purposes of this article, these products are considered HTP.

Results
There are different types of electronic devices, on the market, that heat tobacco and exclusive accessories suitable for the model marketed by each tobacco company.Likewise, there are also various denominations for the tobacco refill used in HTPs, such as tobacco stick, sheets, neostiks, heatsticks and others, depending on the model and manufacturer of the product.
The following image shows the structure of a product that burns or tobacco.It is possible to observe the operating mechanism of the device, as well as the tobacco stick and heatstick suitable for it.We identified 251 records and removed 46 duplicates, subtracting 205 records for title and abstract reading.Once the eligibility criteria were applied, two reviewers selected 46 studies for full reading.In the end, 21 studies were included in the report.The systematization of the search, identification and selection phases of the two studies is represented through the Prisma Flowchart (Figure 2).The studies identified are quite heterogeneous, especially in terms of methodology, products used in the experiments and substances tested not to be rejected.Of the 21 selected studies, a third, i.e., seven will have some type of financing from the tobacco industry.For this reason, the results of the study on the impact of the use of HTPs on the quality of air in indoor environments are organized in three categories: Studies financed by the tobacco industry; Independent studies; and Independent studies of impacts on health.Such categorization was necessary due to the historical, already reported, investment in the tobacco industry in studies and dissemination, both in scientific journals, with results that favor them, and which are often used to disqualify evidence from scientific studies without conflicts of interest (VELICER et al., 2018).
Brazilian legislation prohibits the use of smoking tobacco products of any kind indoors or partially indoors, and these products, to be released for consumption, must prove the absence of impacts on the quality of the environment, and not in comparison of their emissions with conventional cigarettes.Thus, in this study only the results are presented on the products of heated tobacco, even if the original studies made such comparisons.We also took into consideration the possibility that these comparisons, depending on the context, could lead to wrong perceptions, interpretations, and conclusions in relation to the risks of these products.
In the research question of this study, this option is clear when it is made explicit that the comparison will be made with the basal level or the background level, that is, without the use of any product.
Category I: Tobacco industry-funded studies Enomoto et al. (2022) evaluated the impact of the use of heated tobacco products on the air quality of environments simulating residences and restaurants.They point out that there was an increase in total volatile organic compounds, glycerol, tobacco-specific nitrosamines, acetaldehyde, propionaldehyde, n-butyraldehyde, benzene, pyridine, and propylene glycol, in relation to the environment without the use of such products.
In a study by Foster et al. (2018) in which exposure was simulated in three types of environments -residence, office and hospitality -, an increase in formaldehyde (in the residence), acetaldehyde (in the 3 environments), nicotine and particulate matter of the three investigated diameters (in the office and hospitality) and in the total number of particles (in the 3 environments) was observed.
| Page 11 of 30 Kauneliene et al. (2019) simulated the variation in air quality after using a heated tobacco product in a non-operating nightclub and during operation, concluding that the use of IQOS brought a significant increase in the concentration of the number of particulate matter in relation to the background environment (control).They also pointed out that the simultaneous use of IQOS may be associated with an increase in nicotine, acetaldehyde, and particulate matter.Meišutovič-Akhtarieva et al. (2019) found that use of heated tobacco product in a simulated indoor environment resulted in increased nicotine, acetaldehyde, particulate matter compared to "background" and particle concentration.Mitova et al. (2016) conducted a study simulating three environments: office, home, and hospitality.According to the findings, acetaldehyde and nicotine concentrations were increased after using heated tobacco product in the three sites.In Mitova et al. (2019), it was reported that after investigating the use of heated tobacco in a simulated environment of a residence, an increase in nicotine, acetaldehyde and glycerin was observed.And finally, Mitova et al. (2021), this time using simulated home, shop, and restaurant environments, found that the use of heated tobacco increased levels of nicotine, acetaldehyde, glycerine, and (if menthol products are used) menthol relative to background levels, with a corresponding increase in total volatile organic compound values.

Category II: Independent studies
Camalleri et al. (2020) carried out an experiment in a university library, in which they evaluated pollution, in an open environment, resulting from the use of tobacco products, including heated tobacco; and the contribution of the use of tobacco products, smoked outside, on the air quality of a nearby indoor location.They found that, in the external area, there was an increase in particulate matter.The authors also point to a worsening of the indoor air quality, due to the proximity of the use of these products in the nearby outdoor area.They suggest that there should be legislation and measures to protect passive smoking in external areas as well.Cancelada et al. (2019) identified and quantified chemicals released during the use of IQOS in a chamber -an experimental environment.They found more than 100 volatile compounds, of which 33 were identified and quantified.According to a prediction model, in an environment of 48m 2 , air change rate of 1.54h-1 and a maximum of 14 heatsticks consumed in 3h, the concentration of formaldehyde would be 0.14µgm-3, of acetaldehyde 6.6µgm-3 and of acrolein 0.19µgm-3.Prediction results suggest that indoor air quality can be affected in both homes and public spaces, with non-users being exposed to potentially harmful concentrations of carbonyls and volatile organic compounds.
Assessing the impact of the use of heated tobacco (Ploomtech, Glo and IQOS) in two environments simulating a shower box and a room, Hirano et al. (2020) found that the maximum concentrations of nicotine, in the shower box test, varied between the different types of devices studied.Khalaf et al. (2020) analyzed the emission of particulate matter after the use of IQOS in a test room, finding an increase in concentration for all three investigated diameters (≤1 µm, ≤2.5 µm, ≤10 µm).Peruzzi et al. (2020) compared particulate matter emissions from the use of different tobacco products indoors.There was an increase in particulate matter of all diameters and also in total particulate matter during use of all heated tobacco products compared to baseline (before use) levels.Comparisons between all types of heated tobacco products investigated demonstrated that different flavors/additives impact indoor particulate matter emissions, both due to smoke characteristics and different usage patterns (e.g., frequency, depth, nasal or oral exhalation).Protano et al. (2020) also evaluated the emission of particulate matter from the use of different IQOS, Glo and Juul sticks and capsules.All electronic alternatives determined a worsening of PM1 concentration in an indoor environment, with median values varying between devices.The high variability of particle loads was attributed to both the type of stick used and the different way users smoked during the experiments.The results showed that all tested products worsen indoor air quality during use.
In a study published in 2017, Protano et al. evaluated the emission of submicron particles from the use of different tobacco products, including heated tobacco.The study demonstrated an increase in the concentration of particles in the air after using IQOS.They also estimated the accumulation of particle doses in the respiratory system after using IQOS, pointing out that this accumulation would be greater in infants and children.And yet, that the highest percentage of particles would be deposited in the alveolar region, where they could induce inflammation and, once accessing the bloodstream, reach other organs.The authors emphasized that even if an individual smokes alone in an indoor environment, the environment remains polluted and contributes to the exposure of others who live with the smoker.This is particularly worrying for infants and children, who, in addition to being more susceptible than adults to adverse effects, are the age group in the study that absorbed the greatest amounts of submicron particles per kilogram of body weight, of which a large number of very small particles can easily reach the alveolar region.Protano et al. (2016) evaluated profiles of passive exposure to submicromic particles emitted by heated tobacco products (IQOS) and found that, after their use, submicromic particles are released that can be deposited in the airways of a passively exposed subject.In all the experiments carried out, approximately half of the deposited submicron particles were so small that they could reach the alveolar region of passively exposed subjects; an hour spent indoors in which a single IQOS is smoked determines exposure to submicron particles equivalent to that which would occur by spending 10 minutes in a high traffic area.
Ruprecht et al. (2017) found, in their experiment based on the analysis of the smoke emitted by the IQOS into the environment, that the emission of organic matter particles from these devices is significantly different depending on the organic compound.In the smoke from this device, certain n-alkanes, organic acids such as suberic acid, azelaic acid and n-alkanoic acids with carbon numbers between 10 and 19, as well as levoglucosan, were detected, which were emitted at substantial levels from the IQOS.Another important finding is the presence of carcinogenic aldehyde compounds, including formaldehyde, acetaldehyde and acrolein, in IQOS smoke.Savdie et al. (2020) investigated the effect of different tobacco products on air quality in a home and a car, assessing the concentrations of particulate matter, black carbon, carbon monoxide, and carbon dioxide.There was an increase in all evaluated substances, in relation to the control, after the use of the heated tobacco product.
In yet another study that investigated pollution in cars (SCHOBER et al., 2019), the authors state that smoking inside cars is worrying because the concentrations of potentially harmful substances can be very high in such small spaces.Yu et al. (2022) concluded that various types of volatile organic compounds, aldehydes, particulate matter and nanoparticles were produced from the use of heated tobacco products in an experimental indoor environment.The results indicate that such substances affect indoor air quality.

Category III: Independent studies on health impacts
Two independent studies investigated, albeit through simulation or a preliminary exploratory analysis, the possible effects on health from passive exposure to emissions from heated tobacco products.Hirano and Takei (2020) calculated that the excess risk of cancer for individuals exposed to smoke from heated tobacco products would be 2.7x10-6.Imura and Tabuchi (2021), through a cross-sectional study, found that 39.5% of those exposed to smoke from heated tobacco products had some subjective symptom.Non-smoking tobacco product users had the following symptoms when exposed to heated tobacco product aerosol: sore throat (23%), cough (22.5%), asthma attack (10.9%), chest pain (11.8%), eye pain (19.3%), nausea (31.9%), headache (17.7%).Based on these findings, they suggest that respiratory and cardiovascular abnormalities may be related to passive exposure to HTP aerosol.

Synthesis matrix of selected studies
Chart 3 presents the synthesis matrix of selected studies grouped according to author/year, experiment description, evaluated compounds/substances and results.The maximum nicotine concentrations, in the shower test, for 1.0 and 1.8m were 29.3 and 25.9 µg/m3 for ploomTECH, 160 and 111 µg/m3 for Glo and 257 and 212 µg/m3 for IQOS [all greater than tolerated for adverse health events -3.0 µg/ m3].Regarding PM2.5, the lowest values were observed for ploomTECH, 21 and 10 µg/m3 (SD=55.6.6) for 1.0 and 1.8 m, followed by 330 and 99 µg/m3 (SD = 564, 119) for Glo and 492 and 413 µg/m3 (SD = 667, 466) for IQOS.In the room test the nicotine concentrations with the 3 types of HTP did not exceed 3 µg/m3.PM2.5 concentrations measured at 1.5 and 2.5 m away from the user were lower for ploomTECH and IQOS, 6.5 and 7.0 µg/ m3 (SD = 5.8, 2.7), and 7.0 and 6.9 µg/m3 (SD = 11.6,4.0), respectively, and higher for Glo, reaching 102 and 56 mg/m3 The 1st campaign was carried out outside the nightclub, for 3 days and 5 sessions: "background", "background" with 10 people not using the product, 10 people using IQOS simultaneously, "background" with 30 people not using IQOS, and 30 people using IQOS.Each session took 30 minutes with natural ventilation.The 2nd "campaign" also took place in 3 days and on each day, 1 hour before the house opened (background) and 3 hours with the club in operation.On the last day, the measurement of the actual operating situation was extended to an additional 4 hours.

Chart 3. Synthesis matrix of selected studies
Particle number concentration in real time (PNC), CO 2 concentration, relative humidity and temperature, offline carbonyls (acetaldehyde and formaldehyde), nicotine and 3-ethenylpyridine concentration also offline.
The measured distributions were based on PNC (single particles cm-3 or # cm-3) The use of 10 IQOS increased the particle concentration.The maximum peak recorded was 1.2E+5 # cm-3, with a median concentration of 3.6E+4 # cm-3 and 3.5E+4 # cm-3 in Zones 1 and 2, respectively.This was a significant increase over the background indoor environment or with 10 people not using the product.Thirty IQOS users resulted in another significant increase in particle number concentration with a peak value of 1.5E+5 # cm-3, and an average of 1.2E+5 # cm-3 in Zone 1 and 1.3E+5 # cm-3 in Zone 2. The use of 30 IQOS devices did not result in a significant increase in particulate matter concentration compared to the control (background indoor environment), with the median PM2.
Seven smokers received one of the smoking products as a of 2 blocks of 15 sessions each, for a total of 30 sessions (thus giving 15 device/flavor combinations repeated twice).GLO2 was smoked by Smoker 1, IQOS3 by Smoker 2, GLO4 by Smoker 3, IQOS6 by Smoker 4, IQOS1 by Smoker 5, GLO3 by Smoker 6, JUUL4 by Smoker 7, and so on.Emissions of particulate matter with a diameter ≤ 10 µm (PM10), ≤ 4 µm (PM4), ≤ 2.5 µm (PM2.5) and ≤ 1 µm (PM1) were continuously measured under actual use conditions 5 min before, during and 5 min after smoking each product in a room measuring 53m3, with temperature and relative humidity varying between 20 and 23•C and 36 and 40%, respectively.Measurements were carried out in the "cumulative" mode, including the mass of all particles smaller than or equal to the defined size.
One of the authors stated that he consulted for a medical company.Protano et al. (2020) Particulate matter (PM) with an aerodynamic diameter smaller than 10, 4, 2.5 and 1 µm (PM10, PM4, PM2.5, PM1) was measured before and during the use of IQOS®, GLO®, JUUL®, with different types of sticks/sachets, as well as during the smoking of a conventional tobacco cigarette.
The aerosol was mostly in the PM1 size range (>95%).All DEFs determined a worsening of the PM1 concentration in a closed environment, which ranged from very mild for JUUL® -depending on the capsule used -to considerably severe for IQOS® and GLO®.Median values ranged from 11.00 (IQOS3 and JUUL2) to 337.5 µg m−3(IQOS4).The high variability of particle loads was attributed both to the type of stick used and to the different way of smoking of the volunteers who smoked/ vaped during the experiments.At home, there was an increase in all substances evaluated, in relation to the control, after using the heated tobacco product.The concentration of PM10 (87.8 + 51.7 µg/m3) was 4 times higher, of ultrafine particles (35,700 + 11,500 particles/m3) was 7.6 times higher, of carbon black (1.2 + 0.7 µg/m3) was 5.6 times higher and CO2 (2640 + 680 mg/ m3) was 1.5 times higher after using heated tobacco when compared to the control.The use of heated tobacco did not cause an increase in CO.In the car, there was an increase in particulate matter of all evaluated diameters after using a heated tobacco product.The concentration of ultrafine particles (22,100 + 16,800 particles/m3) was 2.8 times higher, of carbon black (0.5 + 0.3 µg/m3) was 0.7 times higher, after the use of heated tobacco when compared to the control.The use of heated tobacco did not cause an increase in CO.The carbon dioxide concentration found was 1020 + 60 mg/ m3.CO2 showed no increase directly associated with nicotine delivery systems, but a trend linked to a higher breathing rate with smoking.No continua...

Final considerations and conclusion
Electronic devices to smoking are a major challenge for global public health, especially for tobacco control.The real impacts on the health of individuals, society and the environment are still not fully known.Regarding heated tobacco products, | Page 25 of 30 studies are even more limited.However, evidence is already beginning to accumulate on the toxicity of its components, which allows inferences about the damage to health.Studies indicate that there are classified by the International Agency for Research on Cancer (IARC) as carcinogenic to humans (Group I), such as formaldehyde, acetaldehyde and acrolein.
The findings of this study indicate that the emissions emitted by heated tobacco products are a source of environmental pollution and point to a worsening of air quality with their use, with special emphasis on the emission of particulate matter, consistently identified in most studies.Other substances, such as nicotine and acetaldehyde, were identified in more than one study, and the list of pollutants investigated and identified at least once is significant.Heated tobacco products produce emissions that can expose people to toxic substances emitted indoors.
Several of these pollutants are recognized as causing disease.However, there is still no evidence, nor conclusive work on the causal relationship between exposure to emissions and the emergence of health problems.The studies identified here already point to possible damage to health, either by simulating the deposit of particles in the respiratory system and excess risk of cancer, or by initial exploratory data on the effects after exposure.So there is a need for more studies by independent researchers to understand the damage caused, since studies on this topic are often funded by the tobacco industry.
Another important issue is that the evaluated emissions of these products are usually done in comparison with cigarette emissions or using a list of priority toxic agents such as, for example, the one used by the FDA in its authorization process for reduced risk products.In this case, the studies do not consider the more than 80 chemical substances, including carcinogenic ones, present in heated tobacco products, as well as the substances that are found in higher concentrations than in cigarettes.Thus, more studies are needed to assess not only the environmental contamination generated by these products, but also their impacts on health.
Another point to be considered concerns the immense diversity of models and products (including hybrid devices), additives, with different toxic substances being used, as well as the great heterogeneity of published works, which can result in different outcomes.
Despite the gaps about the real extent of environmental contamination and damage caused by these products to non-users, the evidence evaluated is sufficient to point out that HTP are capable of degrading ambient air quality with potentially Physis: Revista de Saúde Coletiva, Rio de Janeiro, v. 33, e33SP103, 2023 | Page 26 of 30 harmful substances.Therefore, they should not be used under any circumstances in an indoor environment, so as to avoid contamination of non-users of these products.It is also important to highlight the need to adopt additional measures curb the illegal trade of these products and to reinforce the inspection of the use of electronic devices indoors, accompanied by information campaigns for the population.

Figure 1 .
Figure 1.Structure of the IQOS device -heated tobacco

Figure 2 .
Figure 2. PRISMA flowchart of the selection process of two items