There are different methods of consuming tobacco or its ingredients. These can be broadly classified as unheated, heated, or combusted tobacco, or nicotine only. The non-combusted methods are always being discussed, compared and argued about regarding their THR value or lack of it. Some of these systems are compared below; they can be very different as regards the possible THR rating that might be given to each type of consumption.
1. Combustion methods include:
2. Vapourising can be used to heat but not combust (burn) tobacco:
- Shisha / waterpipes
- HnB cigarettes (heat-not-burn)
- Vapourisers that use solid materials / vegetable matter ('herbal vapourisers')
(the international English spelling is vapouriser or vaporiser, US spelling is vaporizer)
The two important functions of tobacco vaporisers are (1) that they do not burn the tobacco, and (2) they either combine or separate the fuel exhaust and tobacco vapour supply to the user. There is a significant distinction between those with a single air channel for all combustion and vapour products, and those with twin channels where the two systems are separate.
3. Smoke-free, tobacco-free inhalation systems, often flavoured, include:
- Inhalators (small medical devices, often for NRT delivery)
- Ecigs, or more properly EVs 
4. Oral tobacco:
- Swedish Snus
- Other types
Combustion methods in group 1 burn the vegetable matter. The chopped tobacco leaf is combusted, and the smoke produced supplies the original tobacco ingredients but with the downside that numerous pyrolytic compounds are also produced: carbon monoxide, additional aldehydes, numerous carcinogens, and various assorted products of pyrolysis (burning).
Inhalation methods include mouth 'inhale' only, or full inhale. Cigar and pipe users often only draw into the mouth, or may inhale with a comparatively shallow draw. Lung problems normally result from inhalation, so avoiding this would seem to reduce the risk for e.g. lung cancer. It is said that lung cancer from smoking was unknown until cigarettes were invented, but of course this may overlook the fact that identification of cause of death was not accurate at that time.
In the group 2 methods, tobacco is heated but not combusted (burnt).
The important feature is how the air supply for the fuel combustion is separated, or not separated, from the vapour supply channel. There are 3 different classes of device:
2.a. The shisha tabletop pipe type: there is only one air channel. The fuel air supply and exhaust uses the same channel as the tobacco vapour - just the one air inlet and outlet, the outlet being the user mouthpiece.
2.b. The butane type: these portable units usually have two air channels, so the fuel exhaust is separated from the vapour output to the mouthpiece.
2.c. The electronic type: these use a battery and heater coil, so there is no combustion anywhere in the process. There is one air channel but that is not relevant to this type, as no fuel is burnt.
A comparative measure for convenience
It is convenient to use some kind of time-based and/or quantity-based comparative measure when discussing these devices and comparing them to a cigarette. For example, consumption of an HnB 'cigarette' is the same in time (maybe 6 minutes) and quantity (maybe 10 - 15 puffs) as a cigarette. The number of puffs seems of more use as it relates directly to the volume of inhaled aerosol. For shorthand convenience we might term this rough value - say 12 puffs - as one cigarette equivalent session or 1 CES.
Shisha / hookah / argilah / waterpipe / hubble-bubble has existed for a long time in the middle east and elsewhere. The devices are different in the various locations, but generally use either ignited charcoal in a tray below the tobacco, or hot coals above it, and the tobacco may be well-mixed with other materials such as mint. Air is drawn through by sucking on a mouthpiece at the end of a pipe, often flexible. The hot air from the burning charcoal travels through the vegetable matter, heating it but not burning it. There may be more than one pipe (multi-user). With some devices, the air passes through a water cooling chamber. As this class of device has only one air throughput channel, users consume all the combustion products of the fuel as well as the tobacco/plant/fruit vapor (these devices are generally used with a tobacco mix, not pure tobacco; mint, fruit and molasses are commonly used).
The THR value is that no tobacco is combusted; but the negatives are (a) the fuel exhaust is consumed (carbon monoxide and other products of pyrolysis), and (b) a user session can be considerably extended when compared to a single cigarette, perhaps reaching 45 minutes; this could be 10 CES units or more. So the lack of tobacco pyrolysis products has to be balanced against extended inhalation of fuel exhaust and tobacco vapour of many times the quantity represented by a single cigarette equivalent. It means that the THR benefit is limited or possibly non-existent.
HnB cigarettes have been in development for decades and some products have been briefly brought to market - in the USA these were banned, for various reasons (it is overly simplistic to apply any one reason to anything in this marketplace). HnB cigarettes generally employ a charcoal plug at the tip of the 'cigarette', with the body of the tube filled with tobacco as normal. The charcoal tip is lit, and the hot air drawn through the tobacco, which is not ignited. The similarity to shisha can be seen here. Again, this class of device has only one air throughput channel.
Regarding the prohibitions, it may be heard that the FDA banned HnB because of the threat from an unknown new tobacco product, but there are many other applicable reasons. HnB cigarettes will have a considerable risk reduction because no tobacco is burnt and there is just the 1 cigarette equivalent session (cf shisha), although with the single air channel there is a limit to the THR value; we have no idea of the percentages or other way of calculating risk as this requires 30-year studies. Without doubt, disease rates would fall by some degree if all smokers used HnB cigarettes, because it measures up at 1 CES, and there is very little tobacco smoke (it is not logical to suggest there is none whatsoever; there will be some solid particulates). The negative is of course the single air channel that means fuel exhaust products are inhaled.
Tobacco (or 'herbal') vaporizers are typified by the Ploom (regular), Iolite and Launchbox type of device. They generally use a butane heat source although some types are now beginning to use an ecig type of battery, though with a different, specialised head. Hot air is drawn through the tobacco, which vaporizes the compounds contained by the vegetable matter, and delivers them to the air stream. The tobacco (or other material) is not burnt. This class of device often has two air throughput channels - the inhaled air is separate from the combustion air. Clearly there is a significant THR gain.
Battery-powered electronic tobacco vapourisers such as the Ploom Pax use a heating element, so there is no combustion, and only one air channel is needed.
Currently the electronic types or 2-channel butane types are the 'safest' way to inhale heated tobacco products.
It is incorrect to call use of the 2b) and 2c) types smoking since there is no smoke and no fuel exhaust is inhaled. The shisha or HnB type, 2a) here, is a form of smoking since although the tobacco is only heated, the fuel exhaust is also inhaled. The fact that fuel exhaust and multiple CES units are involved with the hookah type make any statement there is a THR benefit hard to justify, or at least quantify.
It is reasonable to say that all forms of vapourising by heating of tobacco but not burning it may have a risk reduction compared to smoking, and some appear far better than others in this respect. Research on such issues is deliberately prevented, either by pressure within the system or by financial pressures including lack of funding. A safer form of smoking is unwelcome anywhere: safe smoking is regarded as a disaster (it can't be taxed highly as the disease resulting would be considerably reduced compared to cigarette smoking; the drug trade for treating sick smokers would be significantly reduced; and the MSA payments would disappear).
It's not entirely clear at this time if all, or any, of these systems can be genuinely included under the THR umbrella. The aerosol product is not smoke and it is not vapour, it is something of a mix of the two that is apparently unclassified currently.
Tobacco vapour - the vapour/smoke product from vapourising chopped tobacco leaf - comes in two distinct types:
Because there are two distinct types of tobacco vapour, it is not correct to discuss them all as if they are the same. Shisha types for example will include carbon monoxide and other products of pyrolysis as the throughflow air has only one channel; some butane types have two separate air throughflow channels, with the inhalation air separate from the combustion air; and the electronic style has a heater element so there is no combustion of any kind, with one air channel, meaning that this style has a better claim to the use of the term tobacco vapour as against smoke or smoke/vapour mix.
As with all gas-phase studies, research not conducted by completely independent researchers is probably best ignored, since the opportunities for perverting the results for commercial reasons are clearly plentiful, judging by the junk that has been published on ecig vapour where it is obvious that researchers have deliberately burned out the hardware in order to create anomalous results.
There is going to be a considerable risk reduction compared to smoking for the non-combustion air throughflow types of tobacco vaporiser, but on the other hand these methods cannot be realistically compared to the modern ultra low risk products in group 3 or even group 4.
These methods are for pure nicotine or flavoured liquids without any tobacco. The nicotine, if used, could come from any source but since tobacco is by far the cheapest, this is where it comes from. Nicotine extraction from tobacco is a major industry due to the demand for pharmaceuticals: there are many factories in China and India that extract nicotine from tobacco (and extremely few elsewhere). There are plenty of other plant sources, Duboisia variants being probably the best , but costs would be hugely increased as there is no agricultural foundation at present and no industrialised extraction processes for such other plant sources .
Medical inhalators supply measured doses of nicotine for inhalation, and are part of the NRT system (nicotine replacement therapy).
Ecigs (more accurately EVs ) supply a liquid aerosol with or without nicotine or flavourings. EVs can be thought of as a re-engineered asthma inhaler, because the desired result has some similarities, some of the refill materials are the same (excipients in common such as PG and glycerol), and with a similar active ingredient delivery method. EVs are built to do what an asthma inhaler does, with a similar payload type and base, but to 'consumerise' the experience and make it as similar as possible to tobacco smoking. Like an asthma inhaler, they are smoke-free, tobacco-free and combustion-free.
These types of nicotine inhaler systems are likely to have a risk elevation over zero so small that it will be invisible clinically. EVs, though, have the ability to be customised in all aspects, so that in practice there is no such thing as 'vaping' - there are a hundred variants. Vapers who take up extreme vaping (with high power, high atomiser temperatures, super high volume consumption, and possibly with creamy-type refills ) cannot possibly experience the same risk reduction compared to smoking as those who are careful about refill choices and use a mid-size ecig with a regular head at low atomiser temperatures. EV-style vaping (to differentiate it from tobacco vaporising) is not a single, homogenous activity and therefore the risk profiles for various usage types are likely to vary.
Liquid vs smoke aerosols
Strictly speaking, vapour is air with some liquid molecules supended in it and which are not visible; and ecig 'vapour' is an aerosol (not a vapour) containing liquid particulates. The term 'liquid aerosol' could be used informally for ecig vapour.
Smoke is an aerosol consisting of air containing solid particulates, which is normally considered to be a visible suspension, but could also be used informally to refer to burnt fuel exhaust with non-visible particulates.
Therefore, although ecig vapour and smoke are both technically aerosols, vapour contains liquid particulates and smoke contains pyrolytic gases (e.g. carbon monoxide) and solid particulates. There will be a significant difference in the effect on the lungs and other systems in the organism; just as there is a difference between inhaling steam in a sauna and smoke in a building fire.
Tobacco vapour from a butane vaporiser is arguably neither vapour nor smoke but a mix of the two. There is no fuel exhaust present, but the hot tobacco vapour will contain both liquid and solid particulates. Enthusiasts will prefer that the inhaled product is referred to as vapour and therefore with the implication it has no solid particulates ('smoke') at all, but this seems hard to support.
As less-risky forms of inhaling tobacco or nicotine have been discussed, we should also mention ST: smokeless tobacco. The Snus model is the proof that THR works, after all, as Sweden is the world leader in reducing smoking prevalence, the world leader in reducing smoking-related mortality, and the world leader in reducing smoking-related morbidity.
There are hundreds of versions of ST, including Asian versions that might even have comparable risk to smoking - and in such cases are often not exactly tobacco: gutka and paan, for example, need to be considered as separate entities from the oral tobaccos available in the Western world. There is chew, dip, snuff, Swedish packaged Snus and loose Snus, and American versions of snus.
However, as we have the advantage of progress, we ought to take it: and that means preference for Swedish Snus against all other types. The genuine Swedish version is produced to the Gothiatek standard and has most of the carcinogens removed. It has no reliably-identifiable health impact. It would be hard to argue that if choice of subtypes is available, an ST consumer should probably consider Swedish Snus first.
There is a very strong argument that modern American oral tobacco products have no more health impact than Snus, since the material analyses and epidemiology appear to support this. However, the advantage of the Swedish situation is that it involves an isolated population as far as stats and studies are concerned, and therefore it is far easier to argue the case: Sweden's national health statistics are unique in the developed world, of course, and this makes the argument considerably stronger. THR has proven results, here, so that no sane opposition can be raised to the proposition. The US situation can only really be seen from modern studies with ST users and the slightly lower smoking prevalence than the norm for plateaued smoking prevalence reduction states (18.5% vs the more typical 20% to 22%), and this difference appears to represent the number of ST users who are already employing the THR solution by using ST. Actual health stats for the US ST user population are deliberately obfuscated in order to protect the smoking economy.
If it is simply a lazy option to use Sweden alone as proof of modern ST's lack of health impact, those of us who do so must accept that accusation. For better information from the considerably less guilty, please see the work of CV Phillips and B Rodu .
Probably the most important things about Snus are:
 Combinations of the three factors (smoking, drinking, HPV) are reportedly additive and possibly synergistic (exposure to more than one factor increases the risk and may possibly multiply it).
 HPV or human papilloma virus is a type of cancer that can be spread by sex, and in the case of oral sex may lead to mouth cancer. These types of exposures may act synergistically, so a smoker who drinks excessively and has exposure to this oral risk factor may be at the highest risk for mouth cancer. The authority on this area of epidemiology is Prof Rodu , whose work should be consulted for further information.
 Rodu is a pathologist who specialises in the oral pathology of tobacco consumption - see:
 See: http://www.ecigarette-politics.com/who-protects-smoking.html
It is interesting to note that commercially-funded propagandists can become millionaires by lying about public health issues. When some unscrupulous academics are paid more than $6 million a year to do so, it inevitably distorts the entire field.
 See: http://www.ecigarette-politics.com/e-cigarette-terminology.html
- scroll to: Duboisia Hopwoodii
 Regulations designed to restrict (or ban) ecigs have nothing to do with public health (obviously) or any desire to control a new form of consumer product with unknown consequences; such laws are purely designed to protect tax revenues, MSA payments, and established industries and pressure groups. Any specific law that is outmanoeuvred by the market will be adjusted to close the 'loophole'. A new nicotine source will be removed by legislation. Cigarette sales are protected, and nothing will be allowed to interfere with that imperative.
 The terms 'electronic cigarette' and 'e-cigarette' are purely marketing terms that have nothing to do with the actual functionality of the devices: they were introduced to sell more product, as the target demographic (at that time) was long-term smokers who were thinking about quitting. We continue to use it as it is successful in doing the designed job (smokers clearly will not switch to something named after a medical device, like 'inhalator' etc.), it is well-known and recognised (vital for social awareness and thus increasing our numbers), and accepted within the user community. Apart from that, it's a really terrible term since vaping has no connection whatsoever with smoking or tobacco, and use of such a confusing term as 'ecigarette' has increasing negatives. A far better term would be EV or electric/electronic vapouriser - as that is what it is. Functionally, it is much closer to an asthma inhaler than a tobacco cigarette; although unlike either, and clearly a completely separate entity, it is far closer to a medical inhaler or inhalator than a cigarette: the emitted product is a liquid aerosol, as with medical inhalers, and not smoke (which is an aerosol comprised of solid particulates and pyrolytic gases, neither of which are present in EV vapour).
 This class of flavouring generally uses diketones, which are thought to have more potential than other types for any quantifiable health impact.
 Or, Foulds et al, 2003. (See References page here for citations.)
 The legal issue is a red herring in any case, as laws to protect cigarette sales by banning THR would simply be reworded to encompass any new industrial source of nicotine . Cigarette sales are protected in order to prevent smoking being banned and to protect the revenues. Any threat is removed by ad hoc legislation - see the instant Snus ban in the UK / EU 23 years ago in 1992, and the current version of that same ban, for ecigs this time, that has received so much pushback from the community (the primary stakeholders), who were clearly more awake this time round.