12.8.1 Construction of cigarettes
Factory-made (ready-made) cigarettes have a relatively simple design with few components (Figure 12.8.1). They consist of a filler of cut tobacco that has been processed and mixed with? with chemical additives, as described in Section 12.6 Additives. The filler is held in a porous paper wrap. Almost all cigarettes contain a filter at the mouthpiece, which is often wrapped in plugwrap paper (an inner paper around the filter) and then tipping paper on the outside. Adhesives are used to fasten these papers. Inks are used to print names and logos on the paper or the tipping paper. Bands of lowered permeability are often added to the paper wrap to reduce the potential for starting a fire (see Attachment 12.2).
The tobacco, additives, papers, inks and adhesives in cigarettes are made up of a wide range of chemicals, some of which are toxic and carcinogenic (see Sections 12.3 and 12.4). When a cigarette is smoked, the tobacco filler, additives, paper wrap, as well as adhesives and ink on that paper are burned. Components that remain unburned include the filter, tipping paper, plugwrap paper and, the adhesives and inks used on these. The burned components undergo chemical reactions during burning that convert them into smoke and ash (see Section 12.4.2). During the production of smoke, many more toxic and carcinogenic chemicals are produced from these chemical reactions.
Despite their relatively simple design, there is considerable variation in the tobacco used and the chemicals added to cigarettes, such as flavourings, resulting in a wide variation in the range of products on sale.
The tobacco industry has modified the design of cigarettes over the past decades. These modifications have included introducing filters, filter ventilation, increased porosity of the paper, changes in length and diameter, use of reconstituted and expanded tobacco and changes to curing and manufacturing techniques (see Section 12.1).2 Some of these modifications, such as the use of filters, were implemented in response to health concerns that started with rising lung cancer cases in the 1950s. Additives have been used to facilitate manufacturing, increase shelf life, mask or reduce the harshness of smoke, impart flavour and aroma, and control burn mechanics, moisture content and nicotine delivery (see Section 12.6).
These additives and other modifications have also served to increase the addictiveness, attractiveness and toxicity of cigarettes, without substantial improvement to their safety in the long term (see Section 12.6).3 In fact, the US Surgeon General’s 2014 report concluded that there has been an increase in the risk of lung adenocarcinoma in smokers resulting from changes in the design and composition of cigarettes since the 1950s. The evidence was insufficient to specify which design changes have been responsible for this increased risk, but suggests that filter ventilation (see Sections 12.8.1.3 and 12.8.2.4 below) and higher levels of tobacco-specific nitrosamines (Section 12.4.3.7) were highly influential.3
All cigarettes sold in Australia must comply with safety regulations requiring reduced fire risk potential (see Attachment 12.2). This legislation requires features that slow the burn rate, such as two lowered permeability bands included within the cigarette paper (Figure 12.8.1). These are two concentric bands of paper or other material that are included in, or applied to, cigarette paper in order to inhibit the burning of the cigarette.4 The bands slow the burning rate by reducing the movement of oxygen into the cigarette and usually stop the full length of the cigarette from burning.5 Despite these regulations, discarded cigarettes still cause a significant number of fires in Australia—see Section 10.16.
12.8.2 Cigarette filters
12.8.2.1 Development of the modern cigarette filter
Prior to the 1950s, cigarettes rarely came with a filter. In response to the increased understanding that smoking causes lung cancer in the 1950s, tobacco companies made what appeared to be genuine efforts to reduce the danger of cigarettes by introducing filters to the majority of products.6 Since the early 1970s, virtually all factory-made cigarettes in Australia have contained filters and these days most smokers who use roll-your-own cigarettes also make them with a filter.
Filters consist of a cylinder of material that is intended to filter out (retain) some of the chemicals in cigarette smoke. They are often made of plastic (cellulose acetate) fibres, paper and/or charcoal.7 The filter is wrapped in a plugwrap paper and over this, a tipping paper, sealed with adhesive (see Figure 12.8.1). Both these papers are porous, allowing for gas exchange.7 Filter ventilation, consisting of microscopic holes in the tipping paper, can modify the way that people smoke and the results of machine testing of cigarettes, as described in Section 12.8.1.3.
The originally intended function of the filter was simple; as the smoker draws air through the cigarette it passes through the filter before becoming the mainstream smoke that is inhaled. Some of the chemicals in the smoke may be absorbed by the filter, with the aim of reducing the amount of toxic chemicals that reach the lungs. Sidestream smoke, and consequently the majority of secondhand smoke, does not pass through this filter (see Section 12.4.1.2).
While the principle that a filter might remove toxic chemicals from the smoke is a simple one, designing cigarettes with a filter that effectively removed chemicals from the smoke was technically challenging for the tobacco industry.6
Cigarettes smoke is an aerosol—consisting of approximately 0.15 mm to 1.3 mm diameter droplets (particles) that float in gases (see Section 12.4.1). The gases in smoke, such as toxic carbon monoxide, are not reduced by cellulose acetate filters, according to research by the tobacco industry.6 Some of the particles in smoke, which collectively make up tar, may adhere to the cellulose acetate filter. However, this sets up a sequence of other effects. By filtering out some of these particles, filters can change the ratio of particles to gases in the smoke. Since the particles contain addictive nicotine and flavours, filtering out these components modified the appeal of cigarettes to the smoker. There were also problems with the increased draw for some filters—the pressure needed from inhalation by the smoker to pull air through the cigarette and the filter.6 Filters produced a barrier to smokers’ attempts to get more tar and nicotine per puff by taking larger puffs. With the increasing strength of filters, the effort of drawing large puffs from high draw-resistance cigarettes can become aversive.8 ,9 To overcome these and other problems, manufacturers introduced filter ventilation (microscopic holes in the tipping paper). Together with the increased permeability of the plugwrap paper, these modifications allowed air to permeate the filter and dilute the smoke restoring the balance between the gas and particle phases of smoke.6 ,9 See Section 12.8.2.2 for more information about filter ventilation.
Activated charcoal is a highly porous substance that can adsorb (hold on the surface) gases and some toxic substances. Adding charcoal to the cigarette filter, in theory, could adsorb some of the toxic gases in smoke, such as carbon monoxide. However, experiments reported in tobacco industry documents showed no difference in the amount of carbon monoxide in the smoke when charcoal was added to cellulose acetate filters.10 When sufficient charcoal is added to cigarette filters, the yields of volatile organic compounds can be reduced under specific laboratory conditions.11-13 However, evidence that using such cigarettes would protect smokers from disease is lacking. Adding sufficient charcoal to cellulose acetate filters was capable of decreasing the amount of damaging carbonyl compounds in the smoke. However, most commercial cigarettes containing charcoal in filters had a minimal effect on carbonyl compounds.12 A comparison of lung cancer rates in Japanese people who did and did not smoke charcoal-filtered cigarettes did not show any protection from the charcoal.14 Charcoal granules from cigarette filters can be dislodged and inhaled by the smoker. This would presumably result in both the charcoal and chemicals adsorbed on the charcoal entering the lungs of smokers, with currently uncharacterised health effects.15
There are aspects of the colour and feel of filters that increase the appeal of cigarettes. Cigarette filters are usually white. Brighter shades of white can be achieved through the addition of pigments such as titanium dioxide. The whiteness of filters may give the illusion of cleanliness, despite the fact that titanium dioxide is toxic (see Section 12.6.5). Research by chemists at R J Reynolds found that manipulating the pH (acid-base balance) in cellulose acetate filters produced a brown colour in the filter once smoked. This brown colour gives the illusion of chemicals being trapped in the filter, potentially influencing the smoker to believe that filtration substantially reduces these chemicals in smoke and the harm that they cause.6 Filters may also stop tobacco pieces from cigarettes from entering the mouth of the smoker during inhalation.16 Filters may be less likely to become soggy during repeated insertion into the mouth than the porous ends of unfiltered cigarettes, potentially improving the experience of smoking.
Some new innovations in filters have recently been introduced into the Australian cigarette market. Recessed filter cigarettes have a hollow tube at the mouth end. The tobacco industry describes these filters as ‘creating a smoother taste and reducing the staining at the mouth end’. Recessed filter cigarettes first entered the Australian market in 2015, described as a ‘taste flow filter’.17 Firm filter cigarettes have a filter that is firmer to touch but looks the same as a regular filter. These may be described as a ‘firm filter’, ‘firm touch filter’ or ‘firmer feel filter’ in the branding of cigarettes.17 Australian smokers perceive that these filter innovations may reduce harm and increase the appeal of the products.17 See Section 10.8.7 for more information about filter innovations.
Flavours embedded inside filters are a recent innovation by the tobacco industry. These products contain a crushable capsule embedded in or near the cigarette filter which, when squeezed, releases concentrated flavouring. See Sections 5.13.2 and 10.8.4.1 for more details.
Discarded cigarette butts, containing filters, ash and many toxic chemicals are a major source of environmental pollution. See Section 10.16.1.1 for more information.
12.8.2.2 Filter ventilation
Filter ventilation refers to perforations in the tipping paper that allow air to dilute the mainstream smoke during inhalation. Whilst making cigarettes appear to be less toxic in laboratory tests, filter ventilation is believed to have increased the health risks of smoking, as described below.
In the 1950s it was shown that tumours developed when tar was painted onto mouse skin, with a dose-response relationship between the amount of tar and the frequency with which tumours developed.7 ,18-20 This led to the belief that simply reducing the tar levels in cigarettes would make them less dangerous. Using machine-measured smoking experiments, the amount of tar (‘tar yield’) in the emissions of different brands of cigarettes could be compared. Despite increasing understanding of the limitations of these testing methods, as described in Section 12.5.2, tar yields were used to compare the relative dangers of cigarettes up until the early 2000s.
Filters (without filter ventilation) were able to reduce tar yields,6 but this produced technical problems for the tobacco industry. Removing too much of the tar (the particles in the smoke aerosol) compared to the gases in the smoke, produced a harsher taste and feel, and modified the appealing flavours of the smoke. The industry solved this problem by introducing filter ventilation: companies added rings of microscopic holes in the tipping paper to increase air diffusion through the filter, diluting the smoke with air.8 High permeability of the tipping paper and plugwrap paper are also important in allowing air to flow in through the filter.21 These changes helped to restore the balance between the particles and the gases in the smoke, improving the flavour of the smoke. Filter ventilation reduced not only tar and nicotine yields, but by diluting the smoke gases, it also reduced carbon monoxide yields – at least when measured by smoking machines.6 ,8
Historically, filter ventilation was the primary means by which the taste, strength and harshness of factory-made (ready-made) cigarettes have been varied by the tobacco industry, followed by the use of filters of differing densities and lengths.8 When the filter ventilation level is increased, the density or length of the filter is usually also increased so as to keep the overall draw resistance of the cigarette within the range that smokers prefer. Longer and/or denser filters generally have higher filtration efficiency, and the combined effects of increased filtration and increased ventilation dilute the smoke so it tastes weaker or ‘milder’ and produces less harshness (the immediate burning/ scratching sensations in the mouth and throat) and irritation (the lingering tingling sensations in the throat and chest).6 Filter ventilated cigarettes with low machine-measured tar yields have been commonly referred to as ‘mild’.
The diluted smoke from filter-ventilated cigarettes could theoretically produce a lower concentration of toxic and carcinogenic chemicals in each puff. However, it has turned out that people who smoked these ‘mild’ cigarettes with filter ventilation did not have better health outcomes than people who smoked regular cigarettes (see Section 12.8.2.3 below). Compensatory smoking is believed to be the main reason for this observation, described in Section 12.8.2.3. It has also been observed in tobacco industry experiments that increasing filter ventilation increases the mutagenicity (ability to change DNA sequences) of the tar by weight.22 This may occur due to the lower temperature of burning in cigarettes with filter ventilation, which changes the products produced in the chemical reactions of combustion and pyrolysis.2 ,23 It is predicted that with the tobacco rod burning less rapidly, decreased airflow through the burning coal tip and lower coal temperatures all led to the formation of more toxic constituents in filter-ventilated cigarettes.2
Modifications such as filter ventilation and increased paper porosity can decrease the size of the aerosol particles. The tobacco industry has made efforts to optimise particle size, with filter ventilation being an important influence.24 The smaller particles from tobacco smoke enter deeper levels of the lungs, leading to more efficient transfer of nicotine to the blood.24 The risk for smokers of developing adenocarcinoma, a subtype of lung cancer, has increased since the 1970s. This increase has resulted from changes in the design and composition of cigarettes, with filter ventilation likely to have contributed, perhaps by promoting deeper inhalation of particles into the lungs.25
12.8.2.3 Compensatory smoking
Compensatory smoking refers to one of the important changes that smokers make to the way that they smoke when they use filter-ventilated cigarettes or low-nicotine cigarettes.
The extra air that enters the smoke through the ventilation holes of cigarettes reduces the overall concentration of nicotine in the smoke. Smokers vary in the level of nicotine they like, smoking each cigarette to get their own target level of nicotine ‘hit’.23 ,26 To get their desired amount of nicotine and feel satisfied, most smokers adapt their smoking method when using cigarettes with ventilated filters. These changes include more frequent puffs, deeper puffs, smoking to a shorter butt length, or covering the ventilation holes with their lips or fingers.23 Smokers may also increase the number of cigarettes that they smoke each day, but in the majority of cases, smokers maintain the number of cigarettes they smoke but compensate by changing puffing behaviour.27
Compensatory smoking results in smokers inhaling a larger volume of smoke and similar levels of toxicant exposure from filter ventilated cigarettes compared with smoking regular cigarettes.9 ,23 Smokers are often unaware that they are smoking differently. They are usually aware of the smoke being less irritating and weaker-tasting but unaware of the mechanisms through which those sensations of ‘mildness’ arise.9 Consequently, many smokers continue to believe the tobacco in ‘smooth’, ‘light’ or ‘mild’ brands is different to that in ‘original’ brands (i.e. the strongest tasting brands).23
When the emissions of filter ventilated cigarettes are tested in smoking machines under standardised puffing conditions, the amounts of tar, nicotine, carbon monoxide and other chemicals are systematically underestimated, as the puffing conditions do not take into account compensatory smoking modifications (see Section 12.5.2). Labelling of cigarette packets with tar, nicotine and carbon monoxide yields, which continued until 2006 in Australia, is therefore misleading, as described in Section 12.5.2.
Tobacco industry documents show that tobacco company personnel were well aware that filter ventilated cigarettes were delivering lower machine-measured yields of tar and nicotine whilst compensatory smoking allowed a higher delivery of nicotine to satisfy the cravings of their addicted consumers.27 They had made a product that performed differently under testing conditions compared to in the hands of smokers.
12.8.2.4 The health effects of smoking cigarettes with filters and filter ventilation
The first filters used in cigarettes from the 1950s did not use filter ventilation. Many smokers in the 1950s and 1960s switched from non-filtered to filtered cigarettes in the hope of reducing their risk of diseases such as lung cancer. Filter ventilation was rare before 1967 but rapidly became an industry-standard after that time.27 By 1981, 93% of cigarettes sold in the US had ventilated filters.28 Many smokers chose to use these cigarettes as they were labelled ‘low tar’, but without the knowledge that they were switching to ventilated filters.
Many studies have investigated whether filters help to reduce harm to cigarette smokers. There are three main questions addressed in detail in this section:
1. Have non-ventilated filters improved health outcomes for smokers compared to using no filter?
Answering this question requires comparing outcomes for people who have smoked the early filtered cigarettes (without ventilation) to those smoking cigarettes with no filter.
2. Do ventilated filters reduce harm compared to using no filter?
Since ventilated filters have mostly replaced non-ventilated ones, this question asks whether the predominant filters used today actually protect from harm, compared to cigarettes with no filter.
3. Do ‘low tar’ (‘mild’) cigarettes improve health outcomes compared to ‘high tar’?
‘Low tar’ cigarettes are usually made using ventilated filters, whereas ‘regular’ cigarettes have unventilated filters. This question asks whether there is any benefit of using ventilated filters compared to unventilated ones, and differs from the first two questions as it compares one type of filter to another.
Comparing the health outcomes for people who smoke different types of cigarettes, such as ‘low tar’ versus regular, or filtered versus unfiltered, is a complicated task for epidemiologists. For studies conducted over a long time period, people often switched to different types of cigarettes. Since cigarette design has changed over the decades, long-term smokers who started using filtered cigarettes may have smoked a combination of filter-ventilated cigarettes and cigarettes with non-ventilated filters. It is therefore difficult to compare the effects of one type of cigarette to another in these people. Case-control studies must rely on the accuracy of people’s memories of what type of cigarettes they smoked and for how long. Cohort studies, which prospectively seek to measure health outcomes, record peoples’ smoking habits progressively over time. These measurements will be less subject to recall bias, but other problems can also affect study conclusions. Distinct differences exist between the types of people who choose different types of cigarettes. People who smoke ‘mild’ cigarettes, often switch to them after smoking other types. They are also more likely to be female than male, to be older and to have higher education levels and higher income. In general, these are people who have more positive health behaviours and outcomes, meaning that bias will be a problem in observational studies of health outcomes due to cigarette choice not being independent of other health-related choices.27
Despite the challenges described above, clear patterns have emerged from studies asking whether cigarette filters can reduce harm to smokers. There is evidence of some protection from the early, unventilated filters compared to cigarettes with no filters, which were common in the 1950s and 1960s (see Question 1 below). However, ventilated filters provide no reductions in harm compared to unventilated filters, and there is no convincing evidence that today’s ventilated filters are reducing harm compared to unfiltered cigarettes. In fact, ventilated filters may have contributed to increased rates of specific types of lung cancer.
Question 1: Have non-ventilated filters improved health outcomes for smokers?
A number of studies have compared the health effects of smoking filtered cigarettes (without filter ventilation) to unfiltered cigarettes. In most of these studies, the presence of filter ventilation was unrecorded. However, filter ventilation was rare prior to 1967, becoming very common by 1981. Studies of smokers prior to 1967 are most relevant to the question of whether non-ventilated filters improved health outcomes compared to unfiltered cigarettes. Unfortunately, there are few such studies and only one that occurred entirely within this timeframe. These studies provide some, if limited, evidence that these filters reduced the risks of poor health outcomes in smokers compared to cigarettes without filters, described below.
- A case-control study compared lung cancer risk for men who used filtered cigarettes compared to those who used non-filtered.29 The outcome measured in this study was cancer diagnosis between 1960 and 1966, taking into account the intensity and duration of smoking. Most of the men in the study had smoked for 30 years or more. Filters had only become widespread in 1955, so men in the filtered cigarette group may have smoked unfiltered cigarettes previously. Men who smoked filtered cigarettes had a reduced risk (RR 0.59) of lung cancer diagnosis compared to smokers of unfiltered cigarettes.6 ,29
- A case-control study of smokers examined rates of lung and laryngeal cancer in people who smoked cigarettes with filters compared to those without filters.30 Data were collected between 1969 and 1976, so long-term smokers of filtered cigarettes may have used a combination of filtered ventilated and unventilated cigarettes. The analysis adjusted for the duration of the smoking habit, inhalation, and butt length. Consistent across different smoking intensity groups, people who smoked filtered cigarettes were less likely to be diagnosed with lung or laryngeal cancer, for both males and females.30
- A prospective study compared rates of lung cancer in men who smoked filtered or non-filtered cigarettes. Over 5,000 smokers were interviewed in 1970 and 1971 to determine their history of filter use. After 5 years of follow-up, the incidence of lung cancer was double for men who had reported using no filters.31
Similar studies from the 1970s showed the same effects of filters on the risk of bladder cancer.27 ,28 ,32
The 1981 and 1982 editions of the US Surgeon General’s report on the health consequences of smoking detail studies that support a lower risk of disease for people who have smoked cigarettes with filters compared to those without filters. On the basis of these studies, these reports concluded that people who smoked filtered cigarettes were at lower risk of cancer of the lung, larynx and bladder.28 ,33 The risk of lung cancer from smoking, however, was far greater than for non-smokers.33 It is likely that most of the smokers in these studies used filters without ventilation, so the conclusions from these studies are most relevant to non-filter ventilated cigarettes.
Question 2: Do ventilated filters reduce harm compared to using no filter?
The health effects of smoking filter-ventilated cigarettes compared to those with no filters have been compared in numerous large prospective studies. Unlike the early studies described above, these studies mostly found no health improvements for people smoking filtered cigarettes compared to unfiltered. Coincident with the increasing use of filter ventilation since the 1970s, there is evidence that filters were no longer preventing cancer and cancer mortality and were not preventing cardiovascular and respiratory diseases in cigarette smokers. The examples below, which are large prospective studies, mostly included people who smoked after 1967 when increasing proportions of smokers using filters were likely to be using filtered-ventilated cigarettes.
- A prospective study recorded lung cancer incidence in people whose smoking habits were tracked from 1978 to 1985.34 Based on this timeline, short-term smokers in this group may have used a higher proportion of cigarettes with filter ventilation, but long-term smokers would have started on non-ventilated filters. A differing risk of lung cancer was only seen in female long-term smokers (>20 years), not in men or people who had smoked for a shorter time period. Female long-term smokers had a lower risk of lung cancer if they used filtered cigarettes compared to unfiltered.34
- A large prospective study of over 18,000 people, published in 1978, measured deaths from cardiovascular and respiratory diseases for people who smoked filtered and unfiltered cigarettes. People who smoked filtered cigarettes mostly smoked mid- to low-tar products, indicating that they used filter-ventilated cigarettes. The study found no differences in mortality between smokers of filtered (probably filter-ventilated) and unfiltered cigarettes, however, there were some decreases in respiratory symptoms for smokers of filtered products.35
- A 12-year prospective study of over 10,000 people tracked their causes of death from 1965 to 1977. These people likely used a combination of filter-ventilated cigarettes and unventilated filter cigarettes, given the time frame of the study. This study found an increase in the deaths from lung cancer in men who used filtered cigarettes that was not statistically significant, and significant decreases in all-cause mortality and coronary heart disease for men who used filtered cigarettes.36 These decreases in mortality and heart disease could be due to bias, as more health-conscious people may have chosen to smoke filtered cigarettes, with better health behaviours leading to better outcomes for heart disease and all-cause mortality.
- A prospective study of 26,000 Norwegian people followed outcomes for smokers from 1965 to 1993. This study compared smokers of factory-made cigarettes with filters (most likely with ventilation for those smoking after 1981) to those without filters. No significant differences were found in the lung cancer rates of people who smoked non-filtered compared to filtered cigarettes in a multivariate analysis taking into account factors such as intensity of smoking.37
Although most studies have found no advantage of ventilated filters compared to no filters, at least one analysis has shown a lower incidence of lung cancer in people who used filters that would likely have been ventilated:
- A study of people in the National Lung Cancer Screening Trial (2002 to 2009) showed that smokers of unfiltered cigarettes were nearly 40% more likely to develop lung cancer and had twice the risk of dying from lung cancer compared with smokers of filtered cigarettes.38
Question 3: Do ‘low tar’ (‘mild’) cigarettes improve health outcomes compared to ‘high tar’.
There are many studies comparing cigarettes with different tar yields as measured by smoking machines. The primary way in which tar yields are varied is by filter ventilation. So these experiments are likely to be comparing cigarettes with greater filter ventilation to those with less or with no filter ventilation, even though the researchers have not necessarily recorded the extent of filter ventilation.
Filter-ventilated cigarettes usually have low tar, nicotine and carbon monoxide yields when tested using smoking machines, as described in Sections 12.5.2. For decades, low-tar cigarettes, described as ‘mild’ or ‘light’, were positioned by the tobacco industry as being a less damaging alternative to regular cigarettes. However, many studies have demonstrated that smokers of these low tar cigarettes (filter ventilated) do not have improved outcomes compared to smokers of regular cigarettes (no ventilation).
Two prospective studies, called the Cancer Prevention Study I (CPSI) and CPSII, together demonstrate poor outcomes for people smoking low-tar cigarettes. Both studies followed-up on a million people, with CPSI starting in 1959 and CPSII in 1982. There were many changes in cigarette design and smoking habits over the twenty years between these two studies. Death rates from lung cancer were higher in the first six years in the CPSII study than in the CPSI study, despite lower tar cigarettes being more popular during the CPSII study.3 ,39 The 40-year follow-up of the British Doctor’s study from 1951 to 1991 was also consistent with the findings from the CPS studies; the risk of dying from lung cancer was greater at the end of this study. In both the CPS and British Doctors’ studies, the risk of dying from lung cancer remained the same for non-smokers, suggesting changes in demographics and other risk factors had not been causing the differences seen in smokers.
Filter ventilation is likely to have contributed to increased rates of adenocarcinoma of the lung
The studies summarised above indicate that while early cigarette filters have prevented some of the health effects of smoking, today’s ventilated filters are not providing the same benefits. There is considerable evidence that using ventilated filters provides no protection compared to cigarettes with no filter, and evidence from the CPSI and CPSII studies indicate the possibility that using a ventilated filter may lead to a greater risk of dying from lung cancer compared to non-ventilated filters. One reason for this is predicted to be an increased incidence and mortality from adenocarcinoma of the lung that has occurred coincident with the rising popularity of filter ventilation.3
The two main types of lung cancer are non-small-cell lung carcinoma and small-cell lung carcinoma. The subcategories of non-small-cell lung carcinoma are adenocarcinoma, squamous cell carcinoma and large-cell undifferentiated carcinoma. Smoking increases the risk of all the main histological types of lung cancer (see Section 3.4.3.3 for more details). The rates of most types of lung cancer have dropped, at least in men, coincident with reductions in the rates of smoking. However, the incidence of adenocarcinoma of the lung has increased since the 1970s. The mortality from adenocarcinoma of the lungs has also increased.3 The proportion of lung cancers that are adenocarcinomas has also dramatically increased, and this effect is only seen in smokers, indicating that changes to cigarettes since the 1970s are responsible.3
The US Surgeon General’s 2014 report concluded that the increased risk of adenocarcinoma of the lung in smokers has resulted from changes in the design and composition of cigarettes since the 1950s. Over the decades since filters and filter ventilation were first introduced, there have been numerous changes to cigarette design. Filter ventilation resulted in changes such as increased puff volume and speed, greater duration of puffing, shortening of the time between puffs and increased depth of inhalation.2 ,3 ,27 In particular, the greater depth of inhalation may be exposing distal airways are that more sensitive to cancer-causing agents in smoke, however, more research is needed to confirm whether this is the mechanism by which ventilation could be increasing rates of adenocarcinoma.2 There has also been an increase in the relative levels of tobacco-specific N-nitrosamines (TSNAs) in cigarette smoke that may have increased the risks from lung and other types of cancer. Other changes to cigarettes have occurred such as modifications of sizes and shapes of the products, agricultural practices, curing and processing of the tobacco, and the porosity of the paper.2 ,3
After assessing available evidence, the US Surgeon General’s 2014 report has stated that the risk of adenocarcinoma of the lung from smoking has increased since the 1960s and there is suggestive evidence that ventilated filters and increased levels of TSNAs have played a role in increasing that risk.3
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References
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