Is Sour E-liquid Safe to Vape?

A couple years ago, sour e-liquid flavors were cropping up everywhere.  As usual, Kai’s Virgin Vapor ignored the trend for the first year or so.  We like to wait and make sure there are no troubling warning signs, the kind that can crop up when a trendy new ingredient is introduced to the market that hasn’t been extensively tested for inhalation safety.  We wait in case there are signs such as a high rate of bad reactions, reports of health issues, allergies or other complaints from vapers. We don’t want our customers or ourselves to serve as guinea pigs so we hold off until there is some level of safety established before we even consider adding a new ingredient to our e-liquids.  A year or so passed and it was clear that the sour trend wasn’t going away and customers started asking us when we were going to come out with a line of pucker flavored e-liquids.  We decided it was time to go in for a closer look.

With a little research we found that it is primarily malic acid that is used in vape juice to impart that pucker flavor.  Malic acid is an organic compound, a dicarboxylic acid to be exact, that is the active ingredient in many tart and sour foods.  It is naturally created during fruit metabolism so it occurs in all fruits and also in many vegetables such as tomatoes.  It’s the malic acid that makes a green apple tart or gives cherries a touch of sourness.  It’s also widely used in the food industry to impart that unique sour flavor to many foods and beverages.  

In fact, it’s malic acid that makes you pucker when you eat Warheads sour candy.  The first burst comes from citric acid. That’s then followed up by the slower burn of malic acid that’s been coated in hydrogenated palm oil (or micro encapsulated if you want to use the more technical term). The palm oil facilitates the slow release of the sour wave as malic acid hits your tongue and the palm oil dissolves. The malic acid hit lasts for about 5 to 10 seconds before it fades.  Then the rest of the candy has only a hint of sour swimming in sugar, that final whisper coming from milder ascorbic acid with another, smaller hit of citric acid for good measure.  



If you’ve ever looked closely at a package of Warheads, you may have noticed the warning, “Eating multiple pieces within a short time period may cause a temporary irritation to sensitive tongues and mouths.”  That warning is due to the malic acid which can irritate the sensitive lining of your mouth and can also cause dental erosion and even canker sores.  With warnings like that we had our doubts about how healthy vaping malic acid might be but we decided to wade in further.

Our chemist ordered a bottle of malic acid for us to play around with and we started diving deeper into researching the health effects.  Because there aren’t many instances where someone inhales malic acid, we found that there really was a dearth of studies on inhalation safety.  

We were able to find MSDS sheets from several companies showing malic acid to be a respiratory irritant. MSDS stands for Material Safety Data Sheets.  They are an important part of good product stewardship for any company and Kai’s Virgin Vapor creates and makes them available for all of our products on our own website.  They outline product safety, occupational safety and any known hazards for a given material used by a company along with what to do in case of exposure. The MSDS from Integra Chemical Company, for example, lists malic acid as a hazard category 3 for inhalation, noting that it may cause respiratory irritation.  It also notes it as a hazard category 4 when ingested: “acute toxicity - oral,” that is “harmful if swallowed.”  There were clearly some possible red flags when it comes to inhaling this as a vape juice additive but we still hadn’t found much specific information.

Finally, we managed to dig up a report on the National Library of Medicine’s website and we hit pay dirt.

“Malic acid and its salts are considered as strongly irritant to the skin and mucosa and as a particular risk to the eyes,” the report read.  

“Mucosa” is a fancier name for mucous membranes.  According to the Encyclopedia Britannica, “Mucous membranes line many tracts and structures of the body, including the mouth, nose, eyelids, trachea (windpipe) and lungs.” The word “lungs,” of course, jumped off the page at us.  And since malic acid is an acid, it’s really not all that surprising that it would be irritating to these sensitive tissues.  

Exposure via inhalation for those handling the additives is also considered to present a risk. Malic acid was irritating in clinical tests,” the National Library of Medicine continued.  Well, there it was then, in black and white.  Malic acid was a known inhalation risk.  

Because we had a Ph.D. chemist on staff at our disposal and we often get quite curious about some of the vaping fads we’ve seen come and go over the nearly a decade we’ve been in business, we decided to run a little testing on our malic acid sample to find out a bit more. Sure, it’s an acid, but just how acidic is it?  

The answer?  Very! We found the pH of the malic acid solution we had obtained was the same as hydrochloric acid.  For those of you who snoozed through chemistry class, we’ll break it down for you.

The pH scale is used to measure acids and bases, generally on a scale from 0 to 14.  A 0 is the most acidic, a 7 is neutral, while a 14 is the most alkaline.  However, because the pH scale is what is known as a logarithmic scale, the difference between a 0 and 14 is much larger than it seems.  Each one unit change on the pH scale (going from say a 1 to a 2) actually corresponds to a ten fold change in the hydrogen ion concentration which is what makes something either acidic or alkaline.   

So where on the scale does hydrochloric acid fall?  It’s a full on 0, meaning it is the most acidic reading possible on the pH scale.  Hydrochloric acid is more popularly known as “stomach acid” or “digestive juice,” the super corrosive acid your body produces in order to digest your food.  Hydrochloric acid is why it sometimes burns the inside of your throat when you throw up, because you are bringing up some of the hydrochloric acid that was busy going to work on the contents of your stomach.  Malic acid generally comes in around a 3 on the pH scale, but there are many variables and the solution that we tested was every bit as acidic as hydrochloric acid.  Does anyone really want to vape something that is capable of breaking down a steak dinner in your digestive tract?  Malic acid was out.

As a side note, as if we didn’t need another reason to rule out adding malic acid to our vape juice, our chemist was using hydrochloric acid to titrate when testing the nicotine levels of each of our e-liquid batches on our GCMS machine (we test each batch to ensure the nicotine level is correct).  That meant we also wouldn’t be able to accurately read nicotine levels with malic acid in our samples.  

Our GCMS Machine
Our GCMS Machine. The doodle on the whiteboard is the chemical formula for nicotine : )


But what about other possible additives to make vape juice taste sour?  Was there another possible ingredient we could use to hit that pucker note?  We found two other ingredients that e-liquid manufacturers were using to imbue e-juice with a sour flavor.  One was citric acid, the subtler acid that gives that first burst of pucker to Warheads sour candy, and tartaric acid, which is stronger than both malic and citric acids.  Could one of these be used to safely create the sour e-liquid flavors our customers were asking for?

The Centers for Disease Control and Prevention (CDC) website lists citric acid as an inhalation hazard.  Symptoms include “cough,” “shortness of breath” and “sore throat.”  It also directs that individuals exposed to inhaled citric acid be referred “for medical attention.”  Ugh, no way were we going to put something in our e-liquids that was going to cause our customers shortness of breath!  

And tartaric acid?  We were afraid to even look it up, given that, with an average pH of around 2.5 it is an even more powerful acid that malic acid but we did anyway. The CDC again reported tartaric acid as an inhalation hazard.  This acid produces, “Burning sensation,” “cough,” “shortness of breath,” and “sore throat.”  Not only should people exposed to inhalation of tartaric acid be referred for medical attention (like those that inhale citric acid), but the CDC went one further and indicated that they should also be administered “artificial respiration if indicated.”

That was it.  We were officially staying seated at the sour vape juice masquerade ball.  

So, is sour vape juice safe to inhale?  Our research resoundingly says no.  Kai’s Virgin Vapor is solidly built on the foundation of providing the purest, cleanest e-liquid possible backed up by research and laboratory testing. We avoid unnecessary health hazards by limiting the ingredients we use to only those that are needed and only using ingredients of the highest quality that we can find.  We sit out the trendy new fads until we can do the research and know that we are not haphazardly introducing ingredients into our e-liquids that present known risks to our customer’s health.  After all, didn’t we all switch to vaping in order to reduce our exposure to the well known health risks of cigarettes?  

Kai’s Virgin Vapor will not be introducing a sour vape juice now or in the future unless and until there is a way to create the flavor that does not expose our customers to known respiratory irritants.  Our lungs are not worth risking for a pucker face.

With the obvious health and safety issues involved in vaping malic, citric and tartaric acids, how did it end up being added to e-liquid?  By the time we looked into it, there were dozens and dozens of companies selling sour candy flavored e-liquids with new lines cropping up every month.  There still are.  Try doing an internet search for “Is Sour E-liquid Safe to Vape?”  At the time of this writing, all you’ll get is a listing of companies trying to sell you sour vape juice.  Did no one pause to look into whether this was a good idea?  It would seem not.  In the most likely scenario, some vaper or e-liquid company simply decided one day that, hey, wouldn’t it be cool if we threw some malic acid in there to make a sour candy vape juice?  And, without another thought, that’s what they did.