There is a choice between two substances, propylene glycol vs. vegetable glycerin, used as the base for the e-liquid that makes vapor for inhaling when heated in e-cigarettes. Both of these substances are humectants. This means they absorb and hold in water to keep things moist. Formulas for e-liquids use either of these substances and sometimes use a combination of both.
This report compares the advantages and disadvantages of propylene glycol vs vegetable glycerin based on both the scientific properties and the general information about user experiences.
Propylene Glycol *
The Agency for Toxic Substances & Disease Registry (ATSDR) describes propylene glycol as a synthetically made substance that is colorless, has almost no odor or taste, and is clear until it turns into a vapor when heated.
Propylene glycol is useful as a solvent for flavorings and food colors. It is on the list of chemicals that are Generally Recognized as Safe (GRAS) and approved by the Food and Drug Administration (FDA) for use in cosmetics, foods, and pharmaceuticals. For these purposes, propylene glycol is considered a non-toxic substance.
The artificial smoke or fog that is used at rock concerts and theatrical performances is made by heating propylene glycol and then spreading the vapor onto the stage or into the audience by a using a ventilator fan.
The long-term effects of inhaling the concentrated vapor of propylene glycol, used for e-cigarettes, have not yet been sufficiently tested. Testing of e-cigarettes, using a propylene glycol based e-liquid, shows that the amount of the carcinogenic compound of formaldehyde is similar to e-cigarettes as coming from tobacco cigarettes. Nevertheless, inhaling the vapor from heated propylene glycol is far less dangerous that inhaling tobacco smoke that contains many compounds that are more toxic.
Propylene glycol is a component of contemporary antifreeze and used for deicing compounds. It replaces the use of ethylene glycol, which is very toxic, in the antifreeze formulas. The term “antifreeze” simply means a substance that lowers the freezing point of water. Being an antifreeze substance is not any indication of toxicity. Salt spread on roads, during winter, is an antifreeze measure. Salt, like propylene glycol, is non-toxic for this use.
After testing for toxicity in rats, rabbits, and dogs, in 1974, the World Health Organization released a report stating that the estimate of acceptable daily intake of propylene glycol is 25 micrograms per kilogram of body weight for a human being.
The ATSDR issued a health risk statement for propylene glycol that notes that adverse reactions to exposure are extremely rare and consist only of allergic reactions.
Vegetable Glycerin *
WiseGeek states that vegetable glycerin, also called “glycerol,” comes from vegetable oil. It is a syrupy sweetener used in foods. It is also an ingredient in cosmetics, such as moisturizers, because of its water retention properties. Glycerin is hydroscopic, which means it is able to absorb water from the air. It is a non-toxic antifreeze because it lowers the freezing point when added to water.
Even though it is sweet, glycerin has fewer calories than sugar so it is a sugar substitute in some low-calorie foods. It is part of the formula for some cough syrups for its throat soothing capabilities.
Dow Chemical’s product safety report on glycerin notes that the substance is on the FDA’s GRAS list, is non-toxic, and is considered safe for use in foods and cosmetics. The one caution is that vapor from heated glycerin may cause respiratory irritation. This has been reported by some e-cigarette users when they first start using a glycerin-based e-liquid and usually disappears after a few days or about one week of using the e-cigarette.
Propylene Glycol vs. Vegetable Glycerin Overall Comparison *
Misthub compared propylene glycol vs. vegetable glycerin. This table shows results from their comparisons converted to a ten-point scale, with ten being the best score possible for a category.
|Rating Factors||Propylene Glycol||Vegetable Glycerin|
|Denseness of Vapor||8||10|
|Temperature of Vapor||10||7|
Here is an explanation of the rating factors that includes information noted by the Quit Smoking community.
Denseness of Vapor *
An e-liquid made with a vegetable glycerin base provides a thicker vapor than an e-liquid with a propylene glycol base. For some, the greater thickness of the vapor from vegetable glycerin is preferable, as it more closely mimics exhaling a big puff of tobacco cigarette smoke.
Having an allergic reaction to either vegetable glycerin or propylene glycol is very rare. There are always a few people out of millions that are allergic to something. Allergic reactions are slightly more likely with propylene glycol. Heavy exposure to the skin might cause a rash for a very few people. Incidents of severe allergic reactions do not exist for either substance.
Propylene glycol is virtually tasteless when vaporized so it does not interfere with the tastes of the flavorings added to the e-liquid. Vegetable glycerin, on the other hand, tastes sweet. For those who prefer a sweeter vapor experience this is a positive thing. Nevertheless, the taste of vegetable glycerin does interfere with the pure taste of other flavorings added to the e-liquid.
Less Gunk *
This is an important consideration for cleaning an e-cigarette or vaporizing system. Vegetable glycerin is stickier and thicker than propylene glycol; therefore the buildup of gunk from using an e-liquid that has a vegetable glycerin base in heavier than one with a propylene glycol base. Propylene glycol based e-liquid is runnier and the wick absorbs it faster, so it is used up more quickly than an e-liquid with a vegetable glycerin base.
No Dryness/Irritation *
Both propylene glycol and vegetable glycerin can cause dry throat and/or respiratory irritation. This is slightly more likely to occur with propylene glycol than vegetable glycerin. Some complain that phlegm builds up from using vegetable glycerin based e-liquids.
Propylene glycol is the more popular of the two compounds, when comparing propylene glycol vs. vegetable glycerin, because it is less thick, easier to handle, and gives a better throat hit.
The one caution here is the production of formaldehyde from the vaping of an e-liquid, based on propylene glycol. Formaldehyde is a known carcinogen. A British Health study found that e-cigarettes cause 95% less harm than smoking tobacco cigarettes. However, e-cigarettes are not 100% safe.
For those concerned about health issues, using e-cigarettes to help quit smoking is a good idea, and then tapering off the use of e-cigarettes as well, to be completely free from all the potential health risks from smoking tobacco, vaping, and nicotine use.
One thing to note for those that use e-cigarettes to help them stop smoking tobacco cigarettes is that withdrawal from tobacco smoking may cause ill effects. Some may falsely believe that these effects come from the use of e-cigarettes. Some of the symptoms that may come up from withdrawal from tobacco use and reduction of nicotine intake include appetite increase, constipation, coughing, depression, dizziness, insomnia, irritability, nausea, and stomach pain.
Temperature of Vapor *
Propylene glycol can be heated to higher temperatures than vegetable glycerin to give a thicker vapor. Vegetable glycerin makes thick vapor at lower temperatures. Some vaporizers allow adjustment of the heating temperature. Higher temperatures also deliver more nicotine. The comfort of different temperatures for the vapor is a matter of personal taste.
Throat Hit *
Propylene glycol based e-liquids give a throat hit that is superior to those based on vegetable glycerin that feels closer to the feeling one gets from smoking a tobacco cigarette.
This is the term for the thickness of the e-liquid. The use of vegetable glycerin makes a thicker e-liquid. The use of propylene glycol makes a thinner, runnier e-liquid.
Mixtures of Propylene Glycol and Vegetable Glycerin *
Because of the popularity of propylene glycol, manufacturers of e-liquids offer more formulas based on propylene glycol than vegetable glycerin. However, the users of propylene glycol may also want the thicker smoke available from using vegetable glycerin. There is a happy compromise between the two.
A satisfactory ratio is one part vegetable glycerin to three parts propylene glycol. The users themselves can make this. Manufacturers are also now offering these blends.
The choice of propylene glycol vs. vegetable glycerin all comes down to personal taste. There is not a definitive answer as to which one is better. Some people like both and alternate between the two. Others like a mixture to have a bit of both experiences.
It is important for consumers to know about the differences, so that they can understand the base ingredients of any e-liquids they buy and the types of experiences that are possible. Product labels give information about what percentage of each base a particular e-liquid contains. Consumers can read the product labels and with the information learned from this summary make a good choice of what e-liquid they prefer for the experience they wish to have.