Vaping propylene glycol and vegetable glycerine may lead to lung inflammation

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Researchers have found that using e-cigarettes with the e-liquid refills containing propylene glycol (PG) and vegetable glycerine (VG) may lead to inflammation of the lungs over a period of time. The results of the study titled, “Effects of Electronic Cigarette Constituents on the Human Lung: A Pilot Clinical Trial,” was published in the latest issue of the journal Cancer Prevention Research this week.

E-cigarette use may lead to lung inflammation finds study - Image Credit: DedMityay / Shutterstock
E-cigarette use may lead to lung inflammation finds study - Image Credit: DedMityay / Shutterstock

The team of researchers, in the pilot clinical trial have found that those who smoked e-cigarettes twice a day for just a month had higher levels of chemicals such as propylene glycol in their blood. This was associated with inflammatory changes in their lungs. The count of the inflammatory cells in their lungs rises over time, speculate the researchers. However, they agree that this was a small study of a short duration and the magnitude of the changes noted in the lungs were small.

This study is a follow up on a recent report of cases of lung injuries associated with vaping across United States. There has been speculation about the amount of damage being caused by vaping. The researchers planned on quantifying the changes in the lungs after use of e-cigarettes, they explained.

The US Centers for Disease Control and Prevention (CDC) states that among those who have experienced lung injuries with vaping, “most patients report a history of using tetrahydrocannabinol (THC)-containing products.” The CDC adds, “Exclusive use of nicotine containing products has been reported by some patients with lung injury cases, and many patients with lung injury report combined use of THC- and nicotine-containing products.”

This was the first “experimental design” study that showed the damage caused by e-cigarettes say the researchers. Lead author Dr. Peter Shields, a medical oncologist at the Ohio State University Comprehensive Cancer Center in Columbus said, “Obviously inhaling stuff is going to have some impact on the lungs. This is another piece of information.” He added, “I would not make the conclusion that this shows that e-cigs are harmful to your health, but one piece of evidence for that. I would say that we have choices in the world and it makes sense that if you're not a smoker, you shouldn't start using e-cigs.”

Min-Ae Song, first author of the manuscript and environmental health researcher at the Ohio State College of Public Health, said in a statement, “Human clinical trials can provide valuable information regarding actual toxicant exposure and risk for disease. Through the randomized clinical trial of healthy never-smokers over a month, we found that an increase in urinary propylene glycol, a marker of inhalation-e-cig intake, was significantly correlated with increased inflammatory response in the lung.”

Shields said, “But it is still unknown what role, if any, nicotine containing e-cigs are involved in the patients with severe respiratory illness. In that context, a lot of us are really looking hard for what might be unique to e-cigs that we wouldn't see in traditional smokers.” For this study the team looked at two constituents of the e-cigarettes refills - propylene glycol and vegetable glycerine. These are used as vehicles to carry nicotine and the flavours of the e-fluids.

For this study the team included 30 youths aged between 21 and 30 years between 2015 and 2017. They did not have a history of traditional smoking or e-cigarettes. The participants were divided into two groups – one of the groups was a control group while the other was asked to use e-cigarettes at least twice a day taking 20 puffs during an hour at one time. To measure the puff count, the refills given to the users had LED screens with a puff counter. The e-cigarette refills used contained 50% propylene glycol (PG) and 50% vegetable glycerine (VG) and no nicotine or flavours. The study duration was for one month.

For all the participants, a bronchoscopy was performed at the start of the study and again five weeks after. The lung tissues, bronchi and the lung health were recorded at these sessions. The team wrote, “Inflammatory cell counts and cytokines were determined in bronchoalveolar lavage (BAL) fluids. Genome-wide expression, microRNA, and mRNA were determined from bronchial epithelial cells.”

Results revealed that there was no significant difference in levels of inflammatory cells among the e-cigarette users and the control group. The levels of inflammatory cells and proteins in the adult lungs were slightly raised however among those who used higher amounts of propylene glycol. The levels of propylene glycol could be measured from the urine samples of the participants. This helped the team analyze the extent of use of this chemical. Shields explained, “So people with higher changes in levels actually inhaled more, and when you look at that, you see an increase in inflammation.”

Shields said that the question now was how much inflammation was too much. He said, “Given that these people were no different than the control group, what it says is that we measured an increase but they were still within the normal range.”

The team of researchers agree that this was a small study with few participants and for only a month. Thus no strong associations could be made between e-cigarette use and lung inflammation. They also write that since nicotine or flavours were absent from the refills, the damage caused by these components is also not assessed in this study. Shields said that, “we have direct evidence for inflammation from an important part of e-liquids,” and this means that if they could look at longer use with e-cigarettes containing nicotine and flavours, they could come up with more concrete results. Song added, “Future studies could be of longer duration, include an assessment of flavors, the effect by varying ratios of propylene glycol and vegetable glycerine, and examine randomization of smokers to e-cigs.”

Authors wrote in conclusion, “The data from this study provide direct safety information regarding the e-cig solvent carriers, PG and VG... Future studies are needed to better understand the clinical significance for the magnitude of the effect by PG and VG, varying ratios of the two and longer duration of use as well as effects of flavors.”

Journal reference:

Effects of Electronic Cigarette Constituents on the Human Lung: A Pilot Clinical Trial Min-Ae Song, Sarah A. Reisinger, Jo L. Freudenheim, Theodore M. Brasky, Ewy A. Mathé, Joseph P McElroy, Quentin A Nickerson, Daniel Y Weng, Mark D. Wewers and Peter G. Shields, Cancer Prev Res, DOI: 10.1158/1940-6207.CAPR-19-0400,

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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  1. Kai-Andreas Degen Kai-Andreas Degen Germany says:

    looking at the results in Table 1.The inflammation markers are only slightly elevated in the non vaping control group at the end of the study.

  2. Gem F Gem F United States says:

    You want long term results of a HEAVY vaper over the past 8+ years?  Your more than welcome to contact me & use me as your Guinea pig to disprove everything this article states.....
    I vape heavily throught the entire day, every day, for the past 8+ YEARS...and have suffered ZERO side effects - in fact, my lung health has actually IMPROVED!
    As a regular smoker for over 30 years, I developed chronic bronchitis (amongst other chronic issues PLUS I have a rare genetic degenerative disease) ,and was able to literally quit smoking cigs the very day I received my advanced ecig products over 8+ years ago.  I am a 'traditional' vaper that used more advanced vaping hardware/ tanks-atomizers, and also have been making my own 'ejuice' for several years now.  If you question whether that makes a difference, yes - the way I vape & the more advanced hardware I use (along with HOW I vape - MTL mouth to lung VS direct lung) is a very big deal, especially when compared to how & what these "kids" are vaping!
    The.bottom line here is that I have quite smoking regulard cigarettes AND my lung health has actually IMPROVED 10 fold - any & all signs of previous health issues associated with cigarettes have completely disappeared...  and honestly, I haven't been sick ever since I started vaping either.  I use both PG & VG, along with nicotine and specific flavoring that are all tested to be DIKETONE FREE.  I do NOT 'cloud chase's, sub-ohm or vape stupid things like THC or anything that contains Vitamin E Acetate. I also tend to stick with the same 'ejuice' recipes bc I like what I like & don't really trust many pre-made juices- especially that may come from China!   There are also many other small specifics that I stick with, that would take too long to explain here - but I suppose you could call me an old school vaper that sticks to the basics.  I do not vape to get high like many of these getting sick tend to do...  which is most likely why they're getting sick in the 1st place.  If there were something truly wrong with vaping the way you are 'supposed to', why aren't there more people like me falling "victim" to this supposed epidemic? There should be tens of thousands of us sick or dying if that was the case... and it would have 1st happened a whole hell of a lot sooner than just lately over the past several months -  again, I have been vaping for over 8 YEARS!  The same applies to the rest of the world - NONE that report anything like what is happening only "lately".  The US is the ONLY COUNTRY THIS IS HAPPENING TO - so exactly what kind of "epidemic" is it really?!
    I truly and honestly wish that people would stop all the MASS HYSTERIA over an EPIDEMIC which IS ONLY A RECENT THING, which IS ONLY IN THE US ALONE!  

    The hypocritical CDC actually put a report out there in 2009 that states that using ecigs with Propylene Glycol could actually make you HEALTHIER ,  so much so that they stated that it possibly had potential to stave off viruses and possibly even the common cold because of its antibacterial properties....  For Pete's sake, VAPORIZED PROPYLENE GLYCOL HAS BEEN PUMPED THROUGH HOSPITAL VENTALATION SYSTEMS FOR DECADES because of that fact!  Now all of a sudden, because kids that have been forced underground to buy black market ejuice from who knows who, with God only knows what in it - aside from the fact that they're also vaping THC & other crazy thing in an attempt to get HIGH, are ALL OF A SUDDEN GETTING SICK,  doesnt seem to be much of a mystery - as a totally innocent industry that has actually saved lives is being used as a scapegoat by now sick kids & their parents BECAUSE THEY DON'T WANT TO FESS UP TO WHAT THEYRE ACTUALLY DOING/ VAPING BEHIND THEIR PARENTS' BACKS...  Take a look on YouTube sometime, and see the crazy crap they try vaping, just in an attempt to get high!

    I'm not about to give up something that saved me from cigarettes, that I thoroughly enjoy - nicotine or.not because of some out of control kids looking to avoid blame for their own actions.  I'm also not about to give up my vaping because some mass hysteria parents create because they cant keep better tabs on what their kids are doing behind their backs either.  Maybe parents should be more responsible & kids should admit their guilt for doing what they have no business or knowledge of what they're actually doing.  Nobody wants to never accept the consequences of their own actions, but are quick to blame somebody else that really has nothing to do with what they're doing because it's easier to play the blame game. Well, I'm not willing to be penalized for the few (or several) rotten apples that are trying to spoil the whole barrel.
    If researchers (and doctors) want to actually learn the truth about what long term effects (or lack of) vaping has, try getting/ studying real people who have been vaping long term, and see the real truth behind it all.  All you have to do is ask.... there are plenty ty of us out there that would happily volunteer real data to make the studies actually valid.


    • Carl Wilson Carl Wilson United States says:

      Pretty wild that you just want to inhale anything without actually researching it. No one in their right mind is telling you that it's worse than smoking cigarettes, which is irrelevant to whether or not there are any dangerous constituents in vaping liquids.

      I'm glad vaping has helped you, but that's no reason not to research these things. In fact, that research might result in vaping becoming an even more favorable alternative to cigarettes! I can almost guarantee you that they won't find it's safe, much less that it will make you "healthier", but they can find alternatives to potentially harmful ingredients.

      Also nicotine is bad for you and you haven't actually quit smoking if you're still vaping lmao. Enjoy lying to yourself

  3. Kim Hawkins Kim Hawkins United States says:

    They use PG in inhalers and inhalers save lives every day. I've been using prescription inhalers for asthma for over 25 years. The only side effect I've ever had is what I call 'inhaler heartburn' which can be completely avoided by not doing anything aerobic for at least 45 minutes to an hour after the last time I use it. I also vape and have not used an emergency inhaler since I quit smoking cigs. And I have found that for me at least, Nicotine is so much less addicting in vape juice. It really makes me wonder what the hell the tobacco companies are putting in their cigarettes to make them more addictive than heroin. And my Pulmonologist is so happy that I quit smoking that he wanted to know what vape I use so he could recommend it to other cigarette smokers who want to quit. It is Not the same as cigs AT ALL.

  4. Robert Howarth Robert Howarth Canada says:

    I started smoking at the age of fourteen when it made me "cool" back in 1985 from which I would smoke on average a 25 pack each day until the age of fifty when I was introduced to Vaping and I fell in love with its smooth non harsh experience when I inhaled a puff. I have to admit also that another factor of my switch was that at the time Vaping was cheaper than cigarettes  I am now fifty two years old and still Vaping Mint eliquid that is 50/50 VG to PG with Nicotine at 20mg/mL and I don't have the phlegm or cough that I did while smoking, or the shortness of breath. Even smelling a smoker after a cigarette has become unpleasant. However I do have some negative points to mention. First is that a cigarette you light up and smoke it. Then when you reach the end you butt it out and your done for a while until you're next one. With Vaping I'll be puffing on it constantly all day except for situations like entering a No Smoking/ No Vaping property like a building, however I have puffed in the bathroom figuring that it is odorless and could be explained as a breath mint. The other factor that I need to mention is if you Vape and ever go camping or out in nature, even outside in your backyard take a extra good look at your device before puffing because the flavorings, such as fruit attract insects, Especially ants that will crawl right inside the vaporizer and become unpleasant when consumed...

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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