Ejuice mixes (VG/PG) safety (Journal Article Inside)

[herbivore21]

So some of you may recall my aversion to PG and VG ejuices due to concerns about degradation byproducts and the large volume of these solvents being boiled and inhales in ejuice preparations.

Unfortunately, it appears that my concerns are starting to be more clearly born out in the scholarly research.

"Aldehyde emissions increased by more than 60% after the device was reused several times, likely due to the buildup of polymerization byproducts that degraded upon heating. These findings suggest that thermal degradation byproducts are formed during vapor generation. Glycidol and acrolein were primarily produced by glycerin degradation. Acetol and 2-propen-1-ol were produced mostly from PG, while other compounds (e.g., formaldehyde) originated from both. Because emissions originate from reaction of the most common e-liquid constituents (solvents), harmful emissions are expected to be ubiquitous when e-cigarette vapor is present."

http://pubs.acs.org/doi/abs/10.1021/acs.est.6b01741 here's the link for the scholarly article I'm citing above.

What this tells us is that even the more 'health-friendly' sounding Vegetable Glycerin, when vaporized in ecig tanks releases 'powerful' respiratory irritant (acrolein), the 'probable carcinogen' Glycidol and more. PG also shares a number of dangerous degradation byproducts.

Here's a diagram from the article showing us the chemical pathway that leads to some such byproducts:

It also appears that there is a buildup of dangerous byproducts emitted by the same cart after extended reuse over time vs first use. As is reported above, the nasties increase the more you use the same cart.

It is of course your decision as to what you are happy with doing with your body, but I share this for anybody at all concerned about limiting exposure to toxic materials.

 

[Deleted Member 1643]

Thanks. This is a relatively new type of exposure that has only very recently become regulated. Flavors are another source of concern. While GRAS for food use, almost all contain one or more substances with occupational inhalation exposure limits. Also, most studies to date look at cig-alikes, very few have looked at sub-ohm atomizers and cloud-chasing.

Vapers who switch from combustible cigarettes frequently experience health benefits, but it's a matter of perspective. Someone who initiates with e-cigarettes may well have an opposite experience. It makes sense to be careful and do your research.

 

[Monsoon]

I found this lengthy and informative article on it in my quick digging on it. I'll try to find more analysis in the ecig community as well. A lot of these studies are hindered by flawed methodologies, the article makes mention that the machine drew enough for a dry puff which would result in a very hot mouthtip and a horrible taste. Most people will never let it go dry after the first time happens so it depends when the toxins are showing up. The online e-cig community has IMO trended towards being ultra anal about safety, they even got a manufacturer (Aspire) to switch to 100% organic cotton in their atomizers because some people were unsure about the safety of the other wicking material inside which worked better.

Also depends on the juices and the atomizers used in the study, the tech is also advancing super quickly too with product updates every few months and product line revamps at least once a year. It feels like the computer industry back in the 90's. I believe there are some other researchers out there like Dr. Konstantinos Farsalinos who are working more closely with those in the e-cig community and working on better testing methods.

 

[herbivore21]

I found this lengthy and informative article on it in my quick digging on it. I'll try to find more analysis in the ecig community as well. A lot of these studies are hindered by flawed methodologies, the article makes mention that the machine drew enough for a dry puff which would result in a very hot mouthtip and a horrible taste. Most people will never let it go dry after the first time happens so it depends when the toxins are showing up. The online e-cig community has IMO trended towards being ultra anal about safety, they even got a manufacturer (Aspire) to switch to 100% organic cotton in their atomizers because some people were unsure about the safety of the other wicking material inside which worked better.

Also depends on the juices and the atomizers used in the study, the tech is also advancing super quickly too with product updates every few months and product line revamps at least once a year. It feels like the computer industry back in the 90's. I believe there are some other researchers out there like Dr. Konstantinos Farsalinos who are working more closely with those in the e-cig community and working on better testing methods.

There are some interesting points in that article. Still, the point that I was raising remains.

I was raising that VG and PG degradation byproducts are shown to include some harmful chemicals here. These chemicals appeared throughout the range of voltages and in both carts tested. This study used two ecig carts, a cheaper single coil cart and a higher end double coil cart. Regardless of the resistance, the lower voltage testing still produced the abovementioned harmful substances.

These aldehydes are of course also found in cigarette smoke in greater amounts still! This means that using ejuices at low or high voltages would still be expected to give you less of these toxic substances than smoking cigarettes.

However, I am speaking to cannabis vaporists here. What we do know from this one is that PG and VG both are known to degrade into bad stuff when heated in an ecig cart. Greater voltages give more of these degradation products than the lesser voltages (as low as 3.3v, which as we know is a very low voltage regardless of the resistance), which produced these toxic byproducts in lesser amounts, but still nonetheless. Dual coils spread the heat across more surface area and so produce the aldehydes at a lesser rate than a single coil at the same voltage and resistance. As you know, VG/PG are the very solvents that soak your wick to prevent dry puffs from taking place, so dry puffs aren't relevant to this specific finding (I agree that they will likely be relevant for other findings though!).

My overall point being that if you don't want any chance of consuming these irritants/probably carcinogens that are known to be created by thermal degradation of VG/PG in ecigs, then you are best off avoiding using VG/PG altogether. This is of course a viable option for cannabis vaporists, who can either use vapes designed for straight cannabis extracts without solvents, or just use distillates that are liquid without the use of solvents. It is up to all of you what you choose to do knowing all of this information of course!

Of course, many will still use VG/PG for nicotine vaping instead of smoking cigarettes. On all accounts, including the study above, this will be a safer option

 

[OldOyler]

There are some interesting points in that article. Still, the point that I was raising remains.

I was raising that VG and PG degradation byproducts are shown to include some harmful chemicals here. These chemicals appeared throughout the range of voltages and in both carts tested. This study used two ecig carts, a cheaper single coil cart and a higher end double coil cart. Regardless of the resistance, the lower voltage testing still produced the abovementioned harmful substances.

These aldehydes are of course also found in cigarette smoke in greater amounts still! This means that using ejuices at low or high voltages would still be expected to give you less of these toxic substances than smoking cigarettes.

However, I am speaking to cannabis vaporists here. What we do know from this one is that PG and VG both are known to degrade into bad stuff when heated in an ecig cart. Greater voltages give more of these degradation products than the lesser voltages (as low as 3.3v, which as we know is a very low voltage regardless of the resistance), which produced these toxic byproducts in lesser amounts, but still nonetheless. Dual coils spread the heat across more surface area and so produce the aldehydes at a lesser rate than a single coil at the same voltage and resistance. As you know, VG/PG are the very solvents that soak your wick to prevent dry puffs from taking place, so dry puffs aren't relevant to this specific finding (I agree that they will likely be relevant for other findings though!).

My overall point being that if you don't want any chance of consuming these irritants/probably carcinogens that are known to be created by thermal degradation of VG/PG in ecigs, then you are best off avoiding using VG/PG altogether. This is of course a viable option for cannabis vaporists, who can either use vapes designed for straight cannabis extracts without solvents, or just use distillates that are liquid without the use of solvents. It is up to all of you what you choose to do knowing all of this information of course!

Of course, many will still use VG/PG for nicotine vaping instead of smoking cigarettes. On all accounts, including the study above, this will be a safer option

Good discussion!

Even saw another thread on FC talking about how when you taste/smell rubber in concentrates, that is probably from a pre-harvest white powdery mildew treatment. Guess who had some in his very first bag 'o concentrates to try a while back?

I am hoping for the day for pure flowers for all (not gonna use the "gee" word here, just sayin'), and give me a press to make rosin. (Don't misunderstand - I am currently a QWET hound, and my shatter is awesome, BUT...I can understand basic science! And now that I have read those awesome articles...)

I guess I am saying I am moving more and more after this to thinking that rosin-pressed wax is the way to go. Entry rig prices seem similar (like at least a 1000mah VV battery pen, dual-coil wicks, and a globe or cannon can be had for under $50) for vaping, I have one currently in this category until xmas. The rosin press itself - that's where the $ gets nasty real, real quick.

Thanks for this thread - you have helped me finally decide on whether I thought the investment into a small rosin-press was worth it. Now, yuppers. I'm (late) middle-aged and have the money if I plan for it. That's an xmas thing, too. So until then, back to my homemade absolutes and slick sheets.



Thanks, and good things back out to you!

(Like wow, joking of course, but anybody want my 1/2 bottle of vape juice mix...? Thought I might use it again even though I am pretty much all wax or flowers now, but after reading all that... )

 

[randomtoker]

I had read both the original study and the SDT response article and felt the findings were in line with what people who vape already have discovered 'intuitively' (for lack of better word). These studies focus on e-cigs which are not vape tanks / RDAs (so to speak). E-cigs use tiny wicks, tiny wick holes, and tiny coils. They taste aweful and produce a terrible experience compared to vape tanks and RDAs. People moved away from the little dispo pens for that reason. It's interesting that they note that 'dual coil' is more safe. They also taste better and lasts longer. Actual vape tanks with proper atomizers, or better still RDAs, take that a massive step further with large wicks, and large coils, spreading the heat across much larger volume of juice instead of squeezing tiny droplets over a tiny wick and coil over and over. Especially when talking about RDA's, people replace wicks very regularly.

I'm happy that the intuitive progression of vape equipment away from pen crap also moved vaping towards safer ingestion.

 

[herbivore21]

I probably won't have time to respond to all of the discussion in this thread on an ongoing basis (writing up my own lab reports on my own research project lol) but I thought I'd throw in this additional explainer from the University of California:

http://www.universityofcalifornia.e...cinogens-not-previously-reported-e-cigarettes

To the kinds of pens used:

I appreciate that many studies in the past have used ecigs that are not the sort of thing that in-the-know ecig users would use. However, this test uses VV mod/tank setups that according to the information here very much represents most ecig users that I know of.

The study used two ecigarettes which I have not been able to specifically identify down to model/cart etc (when I do get this info, I will relay it here). What we do know is that these were each on VV controllers (not likely to be cheap old school pens which IME didn't do this for the most part), one was a cheap, single coil atomizer/tank setup and the other was a more expensive dual coil tank setup.

Each was shown to produce much more dangerous byproducts in vapor over the course of 9 x 50 puff cycles on each cart. Polymerization byproducts (gunk buildup on the coils/wicks) are pointed to as the cause of this - the same gunk gets over-cooked in the same coil until it is replaced/rebuilt (as we know this gunk is hard to completely clean).

Still, a separate finding was the PG and VG specifically, both when in the ejuice formulations used in the study as well as when vaporized alone in the same study were confirmed to produce two 'newly discovered' probable carcinogens in ecig vapor that I mentioned in the OP: Glycidol and Propylene Oxide. The researchers confirmed that these are degradation byproducts from VG/PG by vaping 100% VG and 100% PG respectively in the same ecigs (the diagram in my OP show the chemical pathways in these reactions).

A quote from the University of California link above explains:

However, there have been few if any studies on the safety of heating and inhaling propylene glycol and glycerin. “People are not drinking the liquids—they’re vaping them,” said Sleiman. “So what counts is the vapor.”

The researchers vaporized liquids consisting solely of the solvents to verify that they were the source of the emissions. In all, the researchers detected significant levels of 31 harmful chemical compounds, including two that had never been previously found in e-cigarette vapor—propylene oxide and glycidol, both of which are probable carcinogens.

“Understanding how these compounds are formed is very important,” Destaillats said. “One reason is for regulatory purposes, and the second is, if you want to manufacture a less harmful e-cigarette, you have to understand what the main sources of these carcinogens are.”

They do produce less of some key harmful compounds than cigarettes:

For comparison, conventional cigarettes emit 400 to 650 micrograms of acrolein per cigarette, accounting for both mainstream and sidestream emissions. Assuming 20 puffs on an e-cigarette is equivalent to smoking a conventional cigarette, Gundel said, then total emissions of acrolein for an e-cigarette are about 90 to 100 micrograms.

But as I say above, it was found that both the cheaper single coil on the VV mod as well as the flashier double coil both produced these harmful compounds at every voltage (corresponding increases in concentrations of harmful compounds with increase of voltage were observed in both cases). Of course, the dual coil is spreading the electrical energy over more heater coil surface area hence the degradation will be more gradual on dual coils running on the same amount of juice as the single coil - this likely explains the difference.

My point is that by this information, VG and PG are both known to produce harmful compounds in varying amounts depending on the carts used, but at this juncture have been observed to produce noteworthy amounts in each tested cart, even when using a new, properly wicked cart for the first time at very low voltage (in increasing volumes with more use/higher voltage use of the same cart).

My view is that ecigs/ejuices are almost certainly a good idea for weening oneself off of cigarettes. It is likely as well that even for committed cigarette smokers, these ecigs are still a better alternative to use ongoingly over conventional smoking!

For cannabis users IMHO, we don't need VG/PG in the first place and if these solvents are known to contribute probable carcinogens to the mix when vaped, that rules them right out for me in perpetuity.

You guys can of course make your own decisions

Edit: @OldOyler no problems brother, glad to have helped by providing the info! I'll get back to you in more detail soon with a bit of luck

 

[randomtoker]

I've read this one as well. Your assessment of the article is appreciated, and I like that they studied pg and vg separately.

The equipment is still disposable class pens though. The dual coil pens are essentially still the same as single coil, just 2 of the same poor coils/wicks. Still pen / ecig class. I want to see a study with vaporizers. I don't doubt any of the findings at all, I'm curious to see what variance (if any) exists.

**Edit for clarification: there's too many terms for all the equipment. The pictured vape is an e-cig and there's no specs (that I could find) for what they called the "dual coil".

For example, this is a "dual coil" tank and it is disposable class even though the atomizer is replaceable. It also supports VV power units, but it is not anything like a real tank and mod. The "wick" is slightly thicker than thread, the "wick hole" is the diameter of a pin. It's garbage. http://kangeronline.com/products/mini-protank-3-clearomizer

As well, VV power units are e-cig gear, tap to change between 3 or 5 temps. Everything in these recent studies talks about the toxic elements being present at the later puffs where the temp has climbed. Again, proper mods moved to TC (temperature control), which moderates the voltage and wattage electronically to maintain a target temperature.

Does anyone have details of exactly what equipment is used in these studies. Am I missing an appendix, where that's listed? I'm not arguing the studies, I'm annoyed that they all look at e-cigs, not vaporizers.

 

[stickstones]

Rumors have been around for a long time about the possible dangers of vaping with these mediums, but I prefer some science. I'm starting to see some studies finally being done and figured we could hash it out here. I found this article and thought it was worth consideration. Anyone got an opinion on the validity of the study, or any other studies out there to help us figure it out?

http://onlinelibrary.wiley.com/doi/10.1111/add.12942/abstract

mod note: threads merged at your suggestion

 

[DirtyD]

Wondering about this myself lately, smoked cigs and weed like a chimney for 16 years, I quit cigs altogether, but I smoke an e cig since I quit/ quit smoking and went straight to e cig( .06 nicotine). I definitely feel better/ different now that I'm combustion free, I just wonder how bad e liquid vapor is for our lungs, esp. in long run.... Thanks for starting the thread @stickstones . Cheers, D

 

[stickstones]

I'm the type to err on the safe side, so I'll stay away from PG and VG as much as I can, but I'd like to know if it's necessary.

Here's some guys with good funding doing longer term research. They've figured out a way to determine early on if something might cause cancer.

http://www.nature.com/news/e-cigarettes-affect-cells-1.15015

 

[GreenHopper]

Wondering about this myself lately, smoked cigs and weed like a chimney for 16 years, I quit cigs altogether, but I smoke an e cig since I quit/ quit smoking and went straight to e cig( .06 nicotine). I definitely feel better/ different now that I'm combustion free, I just wonder how bad e liquid vapor is for our lungs, esp. in long run.... Thanks for starting the thread @stickstones . Cheers, D

Same here, switched from the death sticks to a 6mg nicotine solution using a fairly decent sized mod (Smok ALien 220 with big baby beast) about 6-8 months ago.

Health and fitness are definitely benefitting.

I started a fitness routine about a year ago and was really feeling it on my chest when smoking.

If I vape within 30mins of doing a run I find my throat and top of chest becomes dry and raspy. As long as I give it at least 1hr before the run I have no issues.

In terms of long term danger I really have no idea what to expect, I don't think anyone really does.

Very interested in this subject, very happy to see more studies looking into it.

I will say I've seen a whole bunch of misinformation out there from both government and big tobacco. It's getting quite hard to discern what is relevant and what is bullshit.

 

[Deleted Member 1643]

Laboratory studies can raise concerns but rarely alleviate them. E-cig studies are especially problematic because e-cigarettes are so diverse. Cig-alikes and sub-ohm RDA's produce very different exposures. Also, traditional animal inhalation studies have a poor record of predicting effects in humans. For example, rats are obligate nose-breathers and their nasal passages are much better than humans' at keeping harmful substances from reaching their lungs. They also live only two years - not nearly long enough to develop lung cancer in the ways that humans do. In vitro studies, like those mentioned in the Nature article, are very promising, but most regulators are still hesitant to accept their results.

Laboratory studies are also useful for comparing exposures. They give researchers some confidence in saying that VG is not as risky as PG and neither are as risky PEG.

The most relevant information comes from human experience. Large numbers of people have been exposing themselves to PG and VG in e-cigarettes for about a decade. That's a significant amount of time, but some lung diseases can take even longer to develop.

Flavors are a big unknown. Almost all e-cig flavors contain multiple chemicals in flavors that raise concerns when heated and inhaled. Human experience isn't as helpful here because of the great variety of flavors available. Until recently, diacetyl, a buttery flavor that causes "popcorn workers lung" was used to flavor e-liquids. It's unlikely this would have been determined from e-cig exposure alone because it was used in a variety of flavors - but not all. If researchers observed vapers developing the disease, it would be nearly impossible to pinpoint diacetyl as the cause. There could be any number of similarly harmful chemicals in e-liquids going undetected.

 

[stickstones]

I thought the interview on this page with Avrum Spira was very interesting.

http://www.bu.edu/research/articles/behind-the-vapor/

 

[GreenHopper]

I thought the interview on this page with Avrum Spira was very interesting.

http://www.bu.edu/research/articles/behind-the-vapor/

I recommend a documentary called 'A billion Lives'.

Like all sources of info though one has to approach it with a critical mind.

 

[stickstones]

I recommend a documentary called 'A billion Lives'.

Like all sources of info though one has to approach it with a critical mind.

Thanks! Care to summarize?

Here's a recent study on PG with some interesting results:

https://phys.org/news/2016-07-additional-carcinogens-previously-e-cigarette-vapor.html

 

[GreenHopper]

Thanks! Care to summarize?

Here's a recent study on PG with some interesting results:

https://phys.org/news/2016-07-additional-carcinogens-previously-e-cigarette-vapor.html

Summary:

• Interview with the e-cig inventor
• Interview with a bunch of docs
• Interviews with some of the folk who got in early and now run significant sized companies that supply the liquids
• Big tobacco missed the boat on e-cigs so attempted to suppress them with misinformation
• Government in cahoots with them due to some lawsuit that resulted in them getting fixed finances for compensation to be used for anti-smoking campaigns but instead got used for other local gov services.
• Generally e-cigs are considered 95% better than smoking
• Some discussion around regulation

I watched it several months ago so I'm sure there was more to it.

It's about 90mins so worth the watch if you are interested in the subject.

 

[stickstones]

thanks @GreenHopper ...that sounds like one to watch. As I gather info I'm wary of the influence behind the scenes. Mad times we live in!

 

[GreenHopper]

thanks @GreenHopper ...that sounds like one to watch. As I gather info I'm wary of the influence behind the scenes. Mad times we live in!

You are correct to be wary, it's very hard to tell who is backing what and where exactly the info is coming from.

 

[herbivore21]

Rumors have been around for a long time about the possible dangers of vaping with these mediums, but I prefer some science. I'm starting to see some studies finally being done and figured we could hash it out here. I found this article and thought it was worth consideration. Anyone got an opinion on the validity of the study, or any other studies out there to help us figure it out?

http://onlinelibrary.wiley.com/doi/10.1111/add.12942/abstract

Scientific articles (including some of those that you have quoted here) have been shared already man. The answer was clear a ways back. In summary:

VG and PG are not safe. Please don't use them.

Both compounds demonstrably release known/probable carcinogens in dangerous quantities (including glycidol and propylene oxide respectively, which are not even the nastiest byproducts measured) when heated in an ecig cart. Neither is safe, nor necessary to use with cannabis. If you are using it instead of smoking cigarettes, it is still less harmful than smoking cigarettes - but still demonstrably harmful.

 

[KeroZen]

http://www.ecigarette-research.org/research/index.php

@herbivore21: I think that you are too assertive. The two studies you hint about are relatively recent (so not way back) and both have shown that when you get too high in temperature, you start burning the shit out of everything and there are pyrolysis byproducts. But that's expected no?

The older formaldehyde finding study was debunked and linked to dry burning the wicks IIRC. The first study about the two new compounds was deemed to be using unrealistic voltages, and the Wang one in January found formaldehyde only above 450°F.

In the same way we probably release more and more nasty stuff with our dry herbs the closer we get to the combustion point. And I have a personal intuition that high temp dabbing is even worse.

 

[stickstones]

Scientific articles (including some of those that you have quoted here) have been shared already man. The answer was clear a ways back. In summary:

VG and PG are not safe. Please don't use them.

Both compounds demonstrably release known/probable carcinogens in dangerous quantities (including glycidol and propylene oxide respectively, which are not even the nastiest byproducts measured) when heated in an ecig cart. Neither is safe, nor necessary to use with cannabis. If you are using it instead of smoking cigarettes, it is still less harmful than smoking cigarettes - but still demonstrably harmful.

Thanks for chiming in...I must have missed that discussion...was it here or elsewhere?

I've been avoiding PG and VG as a norm, but some of the newer articles out aren't so black and white about it and the levels of the possible carcinogens produced. I'm always wary of these articles and what motivations might be behind them, which makes me hesitant.

It also appears to me like the industry is dumping PG in favor of VG (this is just based on what I am seeing at industry shows, nothing more), but a big part of me thinks that is only for perception and not because we have proved it to be safer than PG. Most of the CBD peddlers are using VG even if they started out using PG a year ago.

Studies on PG seem to be more available than VG at the moment, unless I am missing something.

 

[Deleted Member 1643]

VG and PG are not safe.

Agreed, but many human behaviors aren't "safe". Using alcohol and other drugs (cannabis seems to be uniquely benign), having unprotected sex, etc. The relevant question is whether the risks outweigh the benefits.

Neither is safe, nor necessary to use with cannabis.

True, but vaping e-liquid has its own distinct pleasures.

It also appears to me like the industry is dumping PG in favor of VG (this is just based on what I am seeing at industry shows, nothing more), but a big part of me thinks that is only for perception and not because we have proved it to be safer than PG.

Could be forgetting something, but every comparison that comes to mind reports that VG produces less of the harmful substances assayed, whatever they may be.

Experimenting with RDA builds for undiluted concentrate has renewed interest in vaping nic juice. Not advocating vaping glycols (especially PEG), but believe it's possible to make informed choices. This is not the case with most flavors, however, as there is frequently little or no information available on inhalation exposures.

Still getting used to the welcome interest in health among cannabis users. IME, cannabis use was associated with partying.

 

[grokit]

Great thread

Looking at the links plus a couple I found on my own, these quotes stand out for me:

Regarding vg:
"Dow Chemical make all grades of all these products, and advise that their pharma grade synthetic glycerine is the best choice of all their products for inhalation, and it is supplied to pharmaceutical companies for that purpose. Glycerine is therefore used as the base for inhalable medicines and has multiple licences for inhalation."

Regarding pg:
PG is not 'antifreeze' - it is a chemical that is virtually inert to humans while exhibiting all the properties needed in an antifreeze: very low freezing point, antibacterial, and cheap to make at industrial grade. It is more expensive than 'ordinary' antifreeze, which is toxic, and PG is therefore only used for applications where human or animal contact is likely, since it is completely non-toxic. Therefore it can be used as a winterizing antifreeze for boat and RV lavatory systems, where some human contact may be possible; and for applications close to livestock. If something is used as the carrier for medicines in lung-transplant patients' nebulizers, and the base for injected medicines that do not mix with water, it is reasonable to assume that there are few things less toxic.

https://www.e-cigarette-forum.com/forum/threads/pg-vg-peg.177551/

The part titled, "3. PEG or polyethylene glycol" is especially interesting


edit:

The older formaldehyde finding study was debunked and linked to dry burning the wicks IIRC. The first study about the two new compounds was deemed to be using unrealistic voltages, and the Wang one in January found formaldehyde only above 450°F.

In the same way we probably release more and more nasty stuff with our dry herbs the closer we get to the combustion point. And I have a personal intuition that high temp dabbing is even worse.

I agree with you about vaping dry herbs, that as we get closer to combustion we get more of the toxic by-products that we're trying to avoid by vaporizing in the first place. This happens more often with conduction devices imo.

Here's a link to the research abstract about dry wicks:
http://onlinelibrary.wiley.com/doi/10.1111/add.12942/abstract

"overheating produces an unpleasant taste, called a dry puff, which vapers learn to avoid"

Their conclusion:
Electronic cigarettes produce high levels of aldehyde only in dry puff conditions, in which the liquid overheats, causing a strong unpleasant taste that e-cigarette users detect and avoid. Under normal vaping conditions aldehyde emissions are minimal, even in new-generation high-power e-cigarettes.


edit2:

...every comparison that comes to mind reports that VG produces less of the harmful substances assayed, whatever they may be.

Not all vg is created equally; some versions are very toxic while others are totally inert.

From that same page:
It is thought that glycerine produced as a by-product from biodiesel production should not be used for inhalation, since it is more likely than any other type to be contaminated by the toxic phorbol esters of the Jatropha plant, increasingly used in biodiesel production.

 

[herbivore21]

"Dow Chemical make all grades of all these products, and advise that their pharma grade synthetic glycerine is the best choice of all their products for inhalation, and it is supplied to pharmaceutical companies for that purpose. Glycerine is therefore used as the base for inhalable medicines and has multiple licences for inhalation."

Yes, but these inhalable medications are not necessarily being heated and inhaled (in fact, there is no FDA approved medication that is sold to be heated and inhaled in an ecig cartridge and so the relevance of Dow's above claim is clearly very limited). The formulations using VG for inhalables that I am aware of are for nasal sprays etc. The heating of VG creates glycidol. That is the problem for ecigs. The studies that have found that ecigs produce harmful byproducts from VG were carried out with actual ecigs, rather than the above, which is speculation from a corporation with a direct financial stake in the product in question.

What we also need to understand is that here; Dow are simply saying that the pharma grade of glycerine should be used in any case of products being put into the body for inhalation, rather than the lesser grades (similarly, we should be using pharma grade solvents when extracting meds). This is true, even in ecigs, even if VG is not fundamentally safe to heat and inhale. Impurities in lesser grades of VG may be a concern even for inhaling when not heated. Who knows what quality of VG ecig vendors are using!?

Not all vg is created equally; some versions are very toxic while others are totally inert.

VG is not inert when heated to ecig temps (hell, comparatively very few compounds are!). The problems with what you've written in your last post is that none of that seems to consider VG and PG when being heated and inhaled. Again, the manufacturer of a chemical (like Dow) should never be the one that is listened to about safety claims.

Independent scientific testing and evaluation of safety is always a must. Remember, companies have infamously argued in the past that their products are safe long after they are found to be demonstrably harmful - cigarettes, asbestos etc come to mind (and examples that appear to be coming soon include polymer non stick mats placed on BBQs for cooking food on top of, teflon coated frypans etc - these compounds have comparable safety concerns in vape industry applications in some cases too).

Also @grokit, man that ecigarette forum link post does not cite any scholarly literature but refers to 70 years of literature there. 70 year old research is typically not used to demonstrate claims about materials safety in scholarly argument either btw, especially where chemical safety is concerned. See the above infamous products for examples of stuff that 70 year old research will say is safe, but more recent research has found comprehensively otherwise. We should always look for findings from recent decades. With this said, none of the sources have been cited.

We also need to note that none of the abovementioned refutations regarding studies where suspected 'dry wick' was an issue relate to the study I mention below concerning VG and PG releasing harmful compounds when heated and inhaled in ecigs. Hell, the chemical mechanism of action for the creation of the harmful compounds out of heated VG and PG are even outlined in the study I quote!

@stickstones this is one of the threads I mentioned above with one of the studies that found glycidol (probable carcinogen) and acrolein (a 'powerful respiratory irritant') to be produced even when VG alone heated in various ecigs are various voltages:

http://fuckcombustion.com/threads/ejuice-mixes-vg-pg-safety-journal-article-inside.22290/

The corresponding discussion in that thread outlines many of my thoughts on the topic.

True, but vaping e-liquid has its own distinct pleasures.

Man that shit makes me wheeze and make weird noises when I breathe, feel like my lungs are clogged and feel like I'm choking. I can't describe my experiences with any kind of ejuice as pleasurable lol. Still, a lot of people like sensations that I find unpleasant, so I am not saying that you could not possibly enjoy it

Agreed, but many human behaviors aren't "safe". Using alcohol and other drugs (cannabis seems to be uniquely benign), having unprotected sex, etc. The relevant question is whether the risks outweigh the benefits.

Bro this is just equivocation, which is not something that I recommend when it comes to health decisions. If VG and PG as above are harmful to heat an inhale, and we can cheaply and efficiently heat and inhale cannabis actives in safe ways without using them, then there is simply no justification to my mind to use ecig solvents. I hope we'll see the end of ecig solvent use for cannabis in the future

Could be forgetting something, but every comparison that comes to mind reports that VG produces less of the harmful substances assayed, whatever they may be.

This is true. VG is still not safe, but PG has definitely had a higher number of harmful substances measured as a result of heating in an ecig.

Still getting used to the welcome interest in health among cannabis users. IME, cannabis use was associated with partying.

Some of us are medical users, so the health concerns would be obvious there, but even many recreational cannabis users that I have known are very health conscious (many do not drink a drop of alcohol, only vaporize cannabis, don't use other dangerous drugs and take care of themselves generally). I think that cannabis is going to have a great appeal as legalization progresses for recreational uses by people who don't wanna pay with their health for a good time like too many people sadly do.

I'm always wary of these articles and what motivations might be behind them, which makes me hesitant.

Of all of the sources of information that have been considered on this page so far, these scientific research articles are the most reliable sources of demonstrable information with the least bias present. Science is not infallible (in fact, by definition science can only engage with fallible claims!), as too many dogmatic science fanboys will tell you these days (remember that I am a scientist pointing this out too!). Nonetheless, it is still the most reliable tool that we have to understand the world around us.

We should always remember that while you should cast a critical eye even upon research articles that you read, that in reality the information you get from every other source is not held to the same standards of evidence as a scientific research article, which is the best kind of source to answer a question like the titular one in this thread. Obviously, for our question here, peer reviewed scientific publications should be trusted before you take the word of someone on an ecig forum or someone who manufactures the chemical in question etc.

Holy shit have I written a hell of a lot about PG and VG now