What is propylene glycol ?
Propylene glycol or propane 1,2 diol is organic chemical compound obtained by the petrochemical process.
The result is a translucent, odorless and tasteless liquid used as an anti-caking agent, antioxidant, dough hardener, thickener, stabilizer, solvent, emulsifier and preservative.
Its fields of application concern as much pharmaceutical preparations, cosmetics as the food industry.
Propylene Glycol, a food additive
Although rarely indicated in food products, propylene glycol is ubiquitous.
It is most often associated with flavors but also occupies a prominent place as a solvent.
For this secondary place, it is not listed in the ingredients of the products.
It nevertheless appears sometimes under the code E1520.
It is commonly found in non-alcoholic beverages, frozen foods, artificial sweeteners, artificial and natural flavors, spices, marinades, salad dressings, cake mixes, icings, food colors and bakery products.
Propylene glycol in cosmetics
Very present in our shower gels, shampoo, toothpaste, mouthwashes, perfumes ... propylene glycol is used in cosmetics as a stabilizer.
It thus acts as a preservative while stabilizing the texture of the product, preventing it from melting at high temperatures or freezing at low temperatures. It is a dispersant in perfumery.
Propylene Glycol, excipient in drugs
You will most certainly find propylene glycol in your pharmacy.
Used as C3H8O2 as a solvent, PG is very present in pharmaceuticals in topical, oral and injectable form.
It is also used as a stabilizer in vitamins.
It is found in the excipients of many tablets, syrups, inhalers and injectable solutions.
A substance that absorbs water
Mostly used as a solvent to absorb excess water, PG can lead to a form of dehydration. We will come back to in side effects.
Special effects and propylene glycol
Used in the entertainment world, the PG is known for creating smoke and artificial fogs through smoke machines and thus generating special effects.
The principle is to vaporize by a heating device a mixture of water and propylene glycol which, in contact with the air, forms a cloud of significant steam.
Propylene glycol in tobacco cigarettes
The tobacco industry also uses propylene glycol as a humectant for tobacco (whatever it is, cigarette, rolling tobacco, pipe tobacco and cigars) and thus ensure its preservation.
PG solutions are commonly found to maintain a 70% moisture content in cigar humidors.
Is propylene glycol harmful?
Global health agencies consider this substance safe as an additive.
They evaluate its impact on health in the moderately low category and classify it in the "allergy and immunotoxicity" register with no carcinogenic risk or impact on reproduction.
Propylene glycol is metabolized by the liver, where it is converted to lactic acid and pyruvic acid, then to CO2 and water, a completely normal cycle.
It is not bioaccumulative, which means it is not absorbed by the body.
Thus, used at normal dose or level of exposure, it does not accumulate and is excreted by the kidneys in 48 hours.
It can not therefore create long-term toxicity.
The toxicity of propylene glycol
Health agencies say that propylene glycol can not cause major health problems but requires further scientific research.
The study led by Cotta KI, Stephen CD and Mohammad NU for the Global Journal of Pharmacy & Pharmaceutical Science published May 30, 2017 reviews all available studies on propylene glycol inhalation.
Their findings underscore the lack of human testing, while stressing that animal studies have shown no toxicity at inhalation rates much higher than those used in the e-cigarette.
Propylene glycol in the electronic cigarette
PG is a major ingredient in electronic cigarette products.
It makes up the majority of e liquids available on the market and is part of the homemade e liquid that the vapers make themselves, method called DIY, do it yourself.
If, in the past, the majority of e liquids were composed of 100% propylene glycol, they are now preferred in 50 50, half PG, half vegetable glycerin, to optimize the production of vapor and minimize some side effects.
In DIY flavors and concentrates, propylene glycol plays a conservative role and is very present.
Propylene glycol vs ethylene glycol
The confusion between propylene glycol and ethylene glycol has long been maintained by detractors of the ecigarette.
Ethylene glycol or ethane 1,2 diol is a highly toxic chemical compound used as antifreeze or heat transfer liquid for radiators or coolers, for de-icing aircraft or as a raw material for the synthesis of polyester fiber or resin.
Ethylene glycol has never been used in electronic cigarettes.
Propylene glycol vs propylene oxide
In the same way, confusion has occurred with propylene oxide, a very volatile chemical compound used in the manufacture of polyurethanes.
There too, there has never been propylene oxide in the products of the electronic cigarette.
This substance with the smell of ether likely to explode on contact with the air would surely have made talk about it!
Is propylene glycol an alcohol?
Propylene glycol is a dihydric alcohol but do not worry, it will not make you drunk.
Although in the category of alcohol, it does not have the effects of ethanol, which can be very intoxicating in cocktails!
In the same way, it can not be detected by an alcohol test or EtG test that are only designed for ethanol.
Is inhaled propylene glycol dangerous?
Propylene glycol has been used in food and medicine for over a century.
It does not seem to be a problem when ingested or in dermal contact.
There are many studies done in the past on animals giving direction on its effects in the medium and long term.
The results show that inhaled propylene glycol does not pose a major problem even at high concentration.
Its antibacterial virtues have been used in hospitals and especially in pneumology to clean the air.
Sprayed, it helped to reduce infections without creating side effects.
Other studies have been conducted to analyze the impact of smoke machines.
They may be even more interesting because the mixture used to generate a mist always has propylene glycol and is passively inhaled, which comes closest to the vape.
Thus, a study was conducted on 101 people working in the special effects, close to these machines and its conclusions are consistent with the tests conducted on animals.
With the exception of mild irritation and dry throat, no adverse effects were detected.
It should be noted that the PG used in these machines is not USP grade unlike the one you will find in a vape shop.
Side effects of propylene glycol
Although not having deleterious effects, propylene glycol is not harmless for some and can generate unpleasant side effects.
- The symptoms of PG allergy
Highly discussed on ecig forums, there is still a difference between allergy and sensitivity or inteliance to a product.
In the case of propylene glycol in the ecigarette, we can do this differentiation because unlike the allergy that causes an immune reaction, the PG seems to generate only one form of rejection usually resulting in a cough and / or irritation throat.
Other symptoms may also include headaches, sore throat, shortness of breath and tightness, rash, burning or itching.
Most of these symptoms are more sensitive to PG than an allergy, which is more likely to be allergic contact dermatitis.
A poll showed that about 2% of vapers are PG sensitive.
- The dehydration of the vaper
Propylene glycol is hygroscopic, in clear it absorbs moisture.
Thus, under the effect of vapor, the oral mucosa and throat dry out in the first place.
Eyes and skin can also be impacted.
Beginners are often advised not to forget to drink enough water to overcome this inconvenience.
- A ratio too important
Sensitivity to propylene glycol can only lead to a reduction in its presence in vape juice.
Appearing usually one to two weeks after starting the vape, it is easy to overcome this problem by looking for liquids composed of a mixture of PG and glycerin or even 100% glycerin if the allergy is obvious.
Side effects of smoking cessation
If for some, smoking cessation goes smoothly, it can be very delicate for others, causing many symptoms that can easily be confused with a possible allergy to glycol.
This is the case with cough, irritable throat, headaches and possible skin rashes, which are the first effects of stopping smoking.
Determining an allergy to PG is all the more difficult as quitting is recent.
For example, if you experience a kind of tightness of breath, persistent cough, and migraines and have recently quit smoking, chances are that you would see the effects of smoking cessation more than a propylene glycol rejection.
On the other hand, if, over the weeks of smoking cessation, these unpleasant symptoms persist, the correlation with PG is more obvious.
In any case, it is recommended to adjust the ratio of propylene glycol in your e juices.
The effect of nicotine
Nicotine overdose may have the same consequences as a propylene reaction.
The first clear sign is often an irritation of the throat quite intense that does not give way.
The vaper immediately puts this unpleasant feeling on the PG's account while he does not really check the nicotine level of his liquid.
And when we start in the vape, we do not discern very well the first signs of detoxification.
Headaches, irritated throats are often linked to nicotine. This results in an acceleration of the heart rate which shows a kind of rejection of this substance.
It is then necessary to interrupt and drink abundantly to make disappear these side effects in a pair of hours.
Many testimonials on specialized forums reveal that over the course of weeks of smoking abstinence, the body delivers high doses of nicotine and claims adjustment of the level in liquids.
The vaper therefore evolves by lowering the initial nicotine level.
Very often, the use of the electronic cigarette is made by step to finally reach a ridiculous rate to avoid any unpleasant reaction.
Alternatives to propylene glycol
The easiest way to overcome irritation caused by PG is to increase the ratio of vegetable glycerin in your e liquid.
You will easily find neutral bases with a high ratio of VG, usually 30% PG to 70% glycerine, or even what is called full VG base, composed only of vegetable glycerin.
An alternative based on Propane-1,3-diol, a synthetic diol that can be derived from corn by enzymatic degradation of glucose is also proposed to replace PG.
It remains that this product named vegetable mono propylene glycol is also hygroscopic and seems less studied in the long term.
Consequence of vaping
We will only mention propylene glycol and note that a recent study has shown that the inhaled PG is 89% absorbed by the vaper (94% for nicotine and 92% for vegetable glycerine).
Only 10% of the inhaled substance is found in the ambient air, which allowed the researchers to conclude:
"... the indoor air and the air exhaled by a person contain more volatile organic compounds (VOCs) than the aerosol of an e-cigarette »
Solve a problem of sensitivity
Sensitivity to propylene glycol is proven.
If it is non-existent for some, we know that it is sometimes severe and often moderate for others.
But it is not inevitable.
If the vaper pays attention to the signals his body sends him, he will then try to change the composition of his liquid by introducing more vegetable glycerin to soften it and reduce its irritation.
He will also take into account any signs of smoking cessation against which he can only show patience or overdose nicotine he can counter by reducing the level of his e juice.