This is a discussion that has been going ever since vaping started, and there is no short answer.
All these materials come in different grades and ideally you need the best. They run as follows:
Industrial grade
Agricultural grade
Food grade
Pharmaceutical grade
The difference between all these grades is that the percentage of non-identified ingredients increases as the purity grade decreases. You could call these inclusions contaminants, although these extras are likely to be mostly water plus a small amount of very similar molecules they can't remove without increasing the cost - therefore the higher purity grades cost more. This is why when you read a high-accuracy lab test of e-liquid then you'll see references to these other unwanted molecules (such as ethylene glycol in what is supposed to be PG e-liquid), which demonstrates that industrial or agricultural grade was used. This was likely cheap e-liquid that had cheap ingredients, and of course you get what you pay for. There is no such thing as cheap, good quality e-liquid - obviously. The testing that a vendor needs to do to ensure quality puts the price up, if nothing else.
For retail buyers, you should try and get the USP grade from a chemist / pharmacy. It's likely to be high-quality food grade, and hasn't caused any problems we know of, for either PG or VG. Pharmaceutical grade is similar but of a specified guaranteed purity and has a license for medicinal use. Pharmaceutical grade licensed for inhalation is normally impossible to buy at retail, although in theory that's the best for our usage type.
PG has been used for decades in asthma inhalers without any significant issues. It tends to dry out the upper airway with regular use, and this can cause a problem for some people. For that reason, the inhaler companies are moving to a PG/VG mix (just as we use for vaping), or 'all-VG'.
It may not be VG (vegetable) in medicines now, as there is now a supply of pure synthetic glycerine that in theory is the best excipient (carrier) of all.
Which is best: PG or VG?
With regard to which is best out of PG or glycerine, there is no single answer. Some people are intolerant to one or the other, most of them to PG due to a sore throat etc. Fewer people are intolerant to glycerine although they do exist. It's possible they are actually intolerant to materials other than glycerine that are included, though - as only guaranteed pure material is actually pure. That only comes with a pharmaceutical license for inhalation.
Dow Chemical make both, in all grades, so they make 8 types of PG and VG that could be used for various purposes (probably more, as they likely make PEG as well). They recently changed from advising their pharmaceutical manufacturer customers to use the pharma-grade PG, to advising use of their special pharma-grade glycerine. This is a pure synthetic type designed for inhalation, called Dow Optim.
One opinion is that they don't advise PG use for inhalation due to purely commercial reasons: they want to sell more Optim. This could be wrong, of course. Plenty of inhaled pharmaceuticals are based on PG, and that includes the nebulisers used by lung transplant patients, so clearly there is no immediate need to drop the use of PG. It does cause problems for some, though, and this should be recognised.
The same is true, but to a far lesser extent, for glycerine. We can refer to this material as VG, glycerine, glycerin, or glycerol - it makes no difference. Vegetable or synthetic sources are preferable to animal (carcass) sources. The more correct term for this material is glycerol, as this is the most accurate common name (you don't want to know the chemical names...) [1].
However there are 2 important cautions with VG:
1. Don't buy cheap VG. Some is now coming through as a byproduct of biodiesel production, and it can be toxic. This should just go into industrial-grade glycerine, but the key is probably the price. In this life you get what you pay for, and if it is too cheap to be true, then it's probably too cheap to inhale.
2. Ex-smokers with seriously compromised lungs should probably not use 100% VG. Emphysema patients are at risk of contracting pneumonia, for example, so if you have COPD stage 3 or 4 then you should probably either use Snus and don't vape, or make sure there is at least some PG in the refill you vape. This is because as well as being harmless it is one of the most powerful aerosol bactericides and virucides known, and that's why it's used in lung transplant patients' nebulisers. Pure glycerine is probably not a good idea for such persons, and they will obviously know who they are.
What are these chemicals anyway?
Anything with an -ol suffix is a type of alcohol. Glycols and glycerol are in this group.
All these kinds of materials have different effects on the human organism, for example ethanol (ethyl alcohol or what you drink in whisky) causes intoxication; PG and VG are almost inert though treated as complex carbohydrates, and metabolised then excreted. It has been stated that PG has 33% the intoxicating effect of alcohol - although in the microscopic quantities we inhale (relatively) then this is clearly irrelevant. There is one caveat: a cheap or poorly designed electronic breathalyser for identifying drink-drivers might be fooled by oral PG - we don't know the full story on this yet. A blood test for alcohol can't be fooled though (as far as we know).
Equally, glycerine has been stated as having glucose-like effects, though far reduced in strength, although with the tiny quantities we consume, these types of effects are not of interest. Diabetics (generally) report no issues here in any case.
This does not mean that someone, somewhere, will not have a problem with one of these materials, which can otherwise be regarded as absolutely harmless and inert in the quantities we inhale. In fact, this is virtually guaranteed, as rare genetic types and rare medical conditions are a fact. If you are the 1 in 100,000 or so who suffers transient ill effects from one of these otherwise harmless materials, then that is unfortunate. Luckily there are alternatives. PEG 400 is another choice for inhalation (polyethylene glycol of a specific viscosity). It is not the same as ethylene glycol or EG.
Flavor and vapor
PG presents flavors better, though PEG is best out of the three possible choices (PEG is mainly used in prefilled cartos).
We don't currently support the use of PEG unless GC-MS facilities are available for testing, as PEG has a poor record for contamination with DEG (a toxic glycol used in cheaper anti-freeze). This particular contamination is not really a serious issue because all such things depend on the dose [2], and it is probably impossible to inhale a sufficient amount of such a contaminant to cause poisoning; but it is a weapon to be used by the critics of vaping, so best avoided where possible.
VG creates more vapor. It is slightly smoother and sweeter.
PG is hard on the throat for some people, but if you're in an environment with lots of people with colds and flu - then PG is going to be a good idea
Some people DIY a mix with 5% PG and 95% VG as the carrier, before addition of flavors. There are some benefits to this mix although it isn't commercially available at present (it has all the plus points of an all-VG mix, along with a pathogen negating function). This is, then, a 5/95 PG/VG mix.
Convention for percent format
The convention is to state the mix proportion with PG first no matter which is larger. So the most popular commercial mixes are 70/30 PG/VG, 60/40 PG/VG, and 100 VG. If you have a mix that is 80% VG and 20% PG then it's a 20/80 mix. Don't write it 80/20 VG/PG as this is confusing and leads to mistakes.
Possible risk elevation scenarios
See: http://www.e-cigarette-forum.com/forum/health-safety-vaping/638690-formaldehyde.html#post14957231
----------------------------
[1] There are a multitude of common names and chemical names for these materials, used according to the end-user or market they are aimed at. One option in chemical names is as follows:
PG: propane 1,2 diol
VG: propane 2,3 triol
From this you can see that they are not vastly dissimilar molecules, and both belong to the alcohol group (shown by the -ol suffix).
[2] A basic principle of toxicology is that the dose makes the poison. The main difference between a nutrient or a medicine and a poison is the dose. All materials are toxic in a large enough dose. Both vitamins A and D are vital nutrients in very small amounts but kill in a higher dose (for example search: eating polar bear liver).
All these materials come in different grades and ideally you need the best. They run as follows:
Industrial grade
Agricultural grade
Food grade
Pharmaceutical grade
The difference between all these grades is that the percentage of non-identified ingredients increases as the purity grade decreases. You could call these inclusions contaminants, although these extras are likely to be mostly water plus a small amount of very similar molecules they can't remove without increasing the cost - therefore the higher purity grades cost more. This is why when you read a high-accuracy lab test of e-liquid then you'll see references to these other unwanted molecules (such as ethylene glycol in what is supposed to be PG e-liquid), which demonstrates that industrial or agricultural grade was used. This was likely cheap e-liquid that had cheap ingredients, and of course you get what you pay for. There is no such thing as cheap, good quality e-liquid - obviously. The testing that a vendor needs to do to ensure quality puts the price up, if nothing else.
For retail buyers, you should try and get the USP grade from a chemist / pharmacy. It's likely to be high-quality food grade, and hasn't caused any problems we know of, for either PG or VG. Pharmaceutical grade is similar but of a specified guaranteed purity and has a license for medicinal use. Pharmaceutical grade licensed for inhalation is normally impossible to buy at retail, although in theory that's the best for our usage type.
PG has been used for decades in asthma inhalers without any significant issues. It tends to dry out the upper airway with regular use, and this can cause a problem for some people. For that reason, the inhaler companies are moving to a PG/VG mix (just as we use for vaping), or 'all-VG'.
It may not be VG (vegetable) in medicines now, as there is now a supply of pure synthetic glycerine that in theory is the best excipient (carrier) of all.
Which is best: PG or VG?
With regard to which is best out of PG or glycerine, there is no single answer. Some people are intolerant to one or the other, most of them to PG due to a sore throat etc. Fewer people are intolerant to glycerine although they do exist. It's possible they are actually intolerant to materials other than glycerine that are included, though - as only guaranteed pure material is actually pure. That only comes with a pharmaceutical license for inhalation.
Dow Chemical make both, in all grades, so they make 8 types of PG and VG that could be used for various purposes (probably more, as they likely make PEG as well). They recently changed from advising their pharmaceutical manufacturer customers to use the pharma-grade PG, to advising use of their special pharma-grade glycerine. This is a pure synthetic type designed for inhalation, called Dow Optim.
One opinion is that they don't advise PG use for inhalation due to purely commercial reasons: they want to sell more Optim. This could be wrong, of course. Plenty of inhaled pharmaceuticals are based on PG, and that includes the nebulisers used by lung transplant patients, so clearly there is no immediate need to drop the use of PG. It does cause problems for some, though, and this should be recognised.
The same is true, but to a far lesser extent, for glycerine. We can refer to this material as VG, glycerine, glycerin, or glycerol - it makes no difference. Vegetable or synthetic sources are preferable to animal (carcass) sources. The more correct term for this material is glycerol, as this is the most accurate common name (you don't want to know the chemical names...) [1].
However there are 2 important cautions with VG:
1. Don't buy cheap VG. Some is now coming through as a byproduct of biodiesel production, and it can be toxic. This should just go into industrial-grade glycerine, but the key is probably the price. In this life you get what you pay for, and if it is too cheap to be true, then it's probably too cheap to inhale.
2. Ex-smokers with seriously compromised lungs should probably not use 100% VG. Emphysema patients are at risk of contracting pneumonia, for example, so if you have COPD stage 3 or 4 then you should probably either use Snus and don't vape, or make sure there is at least some PG in the refill you vape. This is because as well as being harmless it is one of the most powerful aerosol bactericides and virucides known, and that's why it's used in lung transplant patients' nebulisers. Pure glycerine is probably not a good idea for such persons, and they will obviously know who they are.
What are these chemicals anyway?
Anything with an -ol suffix is a type of alcohol. Glycols and glycerol are in this group.
All these kinds of materials have different effects on the human organism, for example ethanol (ethyl alcohol or what you drink in whisky) causes intoxication; PG and VG are almost inert though treated as complex carbohydrates, and metabolised then excreted. It has been stated that PG has 33% the intoxicating effect of alcohol - although in the microscopic quantities we inhale (relatively) then this is clearly irrelevant. There is one caveat: a cheap or poorly designed electronic breathalyser for identifying drink-drivers might be fooled by oral PG - we don't know the full story on this yet. A blood test for alcohol can't be fooled though (as far as we know).
Equally, glycerine has been stated as having glucose-like effects, though far reduced in strength, although with the tiny quantities we consume, these types of effects are not of interest. Diabetics (generally) report no issues here in any case.
This does not mean that someone, somewhere, will not have a problem with one of these materials, which can otherwise be regarded as absolutely harmless and inert in the quantities we inhale. In fact, this is virtually guaranteed, as rare genetic types and rare medical conditions are a fact. If you are the 1 in 100,000 or so who suffers transient ill effects from one of these otherwise harmless materials, then that is unfortunate. Luckily there are alternatives. PEG 400 is another choice for inhalation (polyethylene glycol of a specific viscosity). It is not the same as ethylene glycol or EG.
Flavor and vapor
PG presents flavors better, though PEG is best out of the three possible choices (PEG is mainly used in prefilled cartos).
We don't currently support the use of PEG unless GC-MS facilities are available for testing, as PEG has a poor record for contamination with DEG (a toxic glycol used in cheaper anti-freeze). This particular contamination is not really a serious issue because all such things depend on the dose [2], and it is probably impossible to inhale a sufficient amount of such a contaminant to cause poisoning; but it is a weapon to be used by the critics of vaping, so best avoided where possible.
VG creates more vapor. It is slightly smoother and sweeter.
PG is hard on the throat for some people, but if you're in an environment with lots of people with colds and flu - then PG is going to be a good idea
Some people DIY a mix with 5% PG and 95% VG as the carrier, before addition of flavors. There are some benefits to this mix although it isn't commercially available at present (it has all the plus points of an all-VG mix, along with a pathogen negating function). This is, then, a 5/95 PG/VG mix.
Convention for percent format
The convention is to state the mix proportion with PG first no matter which is larger. So the most popular commercial mixes are 70/30 PG/VG, 60/40 PG/VG, and 100 VG. If you have a mix that is 80% VG and 20% PG then it's a 20/80 mix. Don't write it 80/20 VG/PG as this is confusing and leads to mistakes.
Possible risk elevation scenarios
See: http://www.e-cigarette-forum.com/forum/health-safety-vaping/638690-formaldehyde.html#post14957231
----------------------------
[1] There are a multitude of common names and chemical names for these materials, used according to the end-user or market they are aimed at. One option in chemical names is as follows:
PG: propane 1,2 diol
VG: propane 2,3 triol
From this you can see that they are not vastly dissimilar molecules, and both belong to the alcohol group (shown by the -ol suffix).
[2] A basic principle of toxicology is that the dose makes the poison. The main difference between a nutrient or a medicine and a poison is the dose. All materials are toxic in a large enough dose. Both vitamins A and D are vital nutrients in very small amounts but kill in a higher dose (for example search: eating polar bear liver).
