Propylene glycol is widely used as a humectant in a variety of everyday products. It prevents bacteria from thriving in hair and skin care products, such as lotions, shampoos, cosmetics, facial creams, saline eye drops, deodorant sticks, mouthwashes and toothpastes. And, it keeps food items moist and fresh for a long time.
Propylene glycol (PG) is also a common ingredient in pharmaceutical products, including oral, topical and injectable formulations. It’s a major component of oil-based fragrances, aromatic massage oils, and antibacterial lotions because of its ability to retain flavors and scents, which is why PG is also used in food colors and flavorings.
So, if you’ve been using these products in your day-to-day life, then it’s safe to say that you’ve been absorbing a fair amount of propylene glycol – whether in liquid, solid or vaporous form – into your system for many years.
The oral toxicity of propylene glycol is extremely low, and large amounts are required to instigate the dangerous effects. The potential for long-term toxicity is also very low. In one study, rats were given feed with as much as 5% PG over a period of 104 weeks and showed no apparent ill effects. Due to propylene glycols low chronic oral toxicity, propylene glycol is generally recognized as safe (GRAS) for use as a direct food additive. Cases of propylene glycol poisoning are related to either inappropriate levels of intravenous or subcutaneous fluid injection use or the accidental consumption of large quantities by children.
Furthermore, “[Propylene Glycol] is licensed for long-term high-volume inhalation under all employee health regulations,” which is why companies have been using it as a carrier solution for the medicine in asthma inhalants and as the main ingredient in fog machines.
Anti-vaping proponents are quick to point out that this chemical is a main ingredient in antifreeze, but they always fail to note that it’s because PG is a much less toxic substance compared to ethylene glycol and diethylene glycol, the previous glycols used by manufacturers as cooling agents.
These counterpoints may all seem contrived to make PG look harmless. Real-world experimentation, such as the 1947 laboratory-based research on vaporous propylene glycol, should convince you of this chemical’s safety. You’ll immediately see that exposure to PG in everyday products, including e-cigarettes, isn’t something to worry about.
Once Upon a Decades-Old Lab Experiment
Rats and monkeys were divided into two groups. The control groups of each animal were not exposed to concentrated fogs of propylene glycol and triethylene glycol. Meanwhile, the experimental groups of the rats and monkeys were exposed to highly concentrated glycol vapors from 12 to 18 months.
The results were clear. All the rats and monkeys showed relatively normal responses and behavior except for two things. The rats exposed to the thick chemical fog showed consistently higher weight gains. Meanwhile, the monkeys in the experimental group endured some dryness of the skin around their faces.
Next, the scientists reduced the vaporous amounts to just below the saturation points of each type of glycol. When they did this, the lab animals didn’t show any more of these physical symptoms. Furthermore, autopsy investigations of all lab animals showed there were no signs of internal damage to their lungs as well as their bone marrow, kidneys, liver and spleen.
And so, the researchers concluded that:
The results of these experiments in conjunction with the absence of any observed ill effects in patients exposed to both triethylene glycol and propylene glycol vapors for months at a time, provide assurance that air containing these vapors in amounts up to the saturation point is completely harmless.
Propylene Glycol as Vehicle for Nicotine
The reason for using propylene glycol as a combustible solvent in e-liquids is its effective delivery of nicotine in vaporous form. It’s a petroleum-based product and also a form of alcohol. Expect it to burn out quickly when exposed to extreme heat.
Because of this chemical combustion, it’s unavoidable that traces of propylene glycol will find their way into the vapor being inhaled and exhaled by vapers. Before you shout an alarm for public endangerment, however, it’s best to recall that PG has been used as an ingredient in various pharmaceutical products, including prescription drugs used in psycho-pharmacological treatments for anxiety disorder, insomnia and alcoholism.
Take note of this excerpt from a study on the behaviors of rats exposed to vaporous propylene glycol by Japanese researchers in 2010:
Although PG is also used as a vehicle for parenteral administration of hydrophobic drugs, it has been shown that PG itself produces an anxiolytic-like effect and inhibits the central nervous system in ways similar to ethanol (Hanzlik et al. 1939; Zaroslinski et al. 1971; Singh et al. 1982; Lin et al. 1998). Moreover, it has been reported that these effects increase the sedative effect of diazepam in humans (Forrest and Galletly 1988) and the hypnotic effect of pentobarbital in rodents (Singh et al. 1982). These findings suggest that we should remain alert to the intrinsic pharmacological effects of PG when it is employed as a vehicle for injection in psychopharmacological studies.
(Please take note that ethanol is defined by Wikipedia as “the principal type of alcohol found in alcoholic beverages, produced by the fermentation of sugars by yeasts.” Diazepam and pentobarbital, on the other hand, are components of prescription drugs used to treat anxiety, nervousness and insomnia, among other mental health problems.)
Aside from its relaxing effects, propylene glycol has also formidable anti-bacterial qualities. In fact, inhaling small amounts of PG can be advantageous in preventing pneumococci, streptococci and staphylococci strains of bacteria, as evidenced by a 1943 study on the air quality of rooms filled with vaporous propylene glycol.
Pneumococci were killed by amounts of propylene glycol as low as 1 gm. in 20 million cc. of air. Concentrations of 1 to 5 million to 1 to 10 million were required to produce the same degree of killing of streptococci and staphylococci.
Moderate Your Vaping Activities
Though the propylene glycol (PG) used to vaporize the nicotine in e-liquids is generally safe to use, consumers are still warned of the possible side effects they’ll experience as they transition from smoking to vaping. Temporary numbing of the taste buds and dryness in the mouth normally occurs. To overcome these, drink a lot of water and space your vaping sessions responsibly.