There has always been some controversy over e-liquid, from issues as simple as "what do we call this thing?" and which VG/PG ratio is best for which atomizer, all the way to safety concerns of the base and flavoring ingredients.
E-juice or E-liquid?
There are a litany of incarnations of how to refer to ejuice, though usually it comes down to either ejuice, eliquid, or e-juice, e-liquid. Some refer to this as "vape juice" or "vape liquid" or even "sauce", but regardless of what you call it, it's essentially the same. There has been a debate on what we call all of these things since vaping first emerged in 2007, and as a new industry there wasn't really a clear guideline on naming conventions.
Search results, hits per Google by term:
A few years back concerns were raised over whether or not we should refer to e-liquid as "e-juice", due to a potential appeal to children. This will probably never be definitively resolved and will continue to be used interchangeably.
E-liquid is generally comprised of four ingredients:
- Vegetable Glycerin
- Propylene Glycol
- Food Grade Natural/Artificial Flavorings
- Nicotine Extract
VG is vegetable glycerin, or glycerol. This is generally derived from soy, coconut or palm oil, through a process known as hydrolysis. Vegetable glycerin is a humectant, sweetener, and acts as a preservative in many prepackaged foods. This ingredient is literally found everywhere and generally regarded as entirely benign. This liquid is viscous, and is the component that makes e-liquid thicker, thus producing "larger clouds".
PG, or propylene glycol, is used in many of the same applications you will find vegetable glycerin. This is a common ingredient in supplements such as fish oil, in stage "fog machines" (theater productions, concerts where you see a haze) as well as asthma nebulizers to deliver albuterol. This is the non-toxic glycol that is sometimes used in HVAC systems to prevent freezing, which is where the purported anti-freeze claim came in. Occasionally, though not commonly, individual vapers might find PG causes a scratchy throat or cold-like symptoms, and in these cases it is recommended by the general community you look for a high-VG/100% VG (depending on severity) e-liquid to minimize these side effects. PG tends to be thinner than VG.
Flavoring is exactly what it sounds like. This comes from both natural and artificial sources, and all of these are GRAS for consumption (food industry). There are a couple of ingredients that are controversial in flavoring, most notably flavors containing diacetyl (butter notes). From the Diacetyl article on Wikipedia:
Workers in several factories that manufacture artificial butter flavoring have been diagnosed with bronchiolitis obliterans, a rare and serious disease of the lungs.
That said, a study conducted at the Department of Environmental Toxicology, University of California, Davis, by Kazutoshi Fujioka and Takayuki Shibamoto, found that the average diacetyl exposure from vaping to be 750 TIMES LOWER than from smoking combustible cigarettes. It warrants noting that there is not a single documented case of popcorn lung caused by smoking traditional cigarettes.
Nicotine is usually blended into a VG or PG base then added to a formula to achieve the desired MG strength. This nicotine extract is traditionally extracted from tobacco leaves, though contains none of the original tobacco material post-extraction. There are a few companies now using synthetic nicotine (TFN: tobacco-free nicotine), though per the most recent information we have, they will also be subjected to the deeming rule same as traditional nicotine extract per the "intended use" guidelines.
Nicotine extracts are free from tobacco-specific nitrosamines, oxides, and beta-carbolines, as they are formed from the presence of both nicotine and tobacco alkaloids, the latter of which isn't present in the extract. Most labs manufacturing nicotine extracts for e-liquid manufacturers will provide comprehensive GC/MS (gas chromatography tandem mass spectrometry) or similar testing of their product to provide a complete chemical analysis breakdown of the constituents.
Some tobacco extracts for flavoring may still contain some nitrosamines, oxides and beta-carbolines, though most flavoring manufacturers do not, and these carcinogens are easily avoided by simply not consuming products with tobacco flavoring. If ingredients past this are a concern, many manufacturers provide lab reports of the contents of their products.
At one point there was a question as to whether or not e-liquid contained heavy metals, though these claims have been vetted and when compared to a Drinking Water Directive sampling conducted by the EU, you would generally consume 10x more heavy metals drinking plain tap water than you could consume via e-liquid products. When it comes to safety concerns and controversy, it's vitally important to review all of the presented evidence and weigh it against existing similar evidence. (A particularly compelling example is the case against Dihydrogen Monoxide, where when polled people supported banning water.)
VG/PG ratios are another contested issue. General consensus looks something like:
VG for clouds/dripping atomizers.
PG for flavor/tanks.
Most e-liquid now hovers around a 60/40 to 70/30 VG:PG ratio, meaning a liquid labeled 70/30 would contain 70% vegetable glycerin to 30% propylene glycol.
Tank atomizers used to be where "the flavor is at". The restricted airflow of the tube leading to the drip tip would condense the vapor itself, and the smaller size of the chamber would heat up warmer than if you were using a super airy dripping atomizer, so the flavor would become condensed with the vapor. Blends at this time could go as high as 30% flavoring, which usually is comprised of a propylene glycol base.
Tanks could be run at a lower wattage, with higher ohm coils, so you would require less e-liquid to achieve a desirable vapor. By that same measure, nicotine ranges ran higher, topping out around 24/36mg. It wouldn't be unusual to run a coil 1.5-2ohms, at 10, 15 watts, using a 24mg/ml e-liquid.
Since the inception of this concept, vaping has evolved considerably. Now we're using higher wattage devices, lower ohm coils on RDAs (rebuildable dripping atomizers) with a ton of airflow, to produce bigger clouds. The quantity of e-liquid inhaled has increased, as has the flavor production. Current e-liquids tend to contain anywhere from 10-20% flavoring, and many manufacturers will mix "MAX VG", which is to say they haven't diluted the liquid past what PG the flavorings contain, often also meaning the nicotine is from a VG base.
Most flavoring is PG-based, which is to say that it counts toward the PG part of the blend. More flavor manufacturers are releasing VG-based flavors than before, so it's possible to have 100% VG e-liquid. If a juice were 60/40, it was likely the manufacturer would have to add additional PG to thin out the formulation.
While all of this can sound a little daunting, ultimately it comes down to trial and error to determine which combination of VG/PG and nicotine level you prefer. With the sheer wealth of devices still available on the market today, combined with such a massive variety of products, there isn't any one "correct" way to vape.