Propylene Glycol; Harmless or Health Hazard?

 The development of cannabis user consumption products has
grown exponentially over the last few years with both the legalization of
recreational cannabis in Washington State and Colorado, and the growing
interest and acceptance of cannabis as medicine throughout the world.

Many of the cannabis products being manufactured today
use various solvents or chemical additives during production, distillation, and
packaging. Types of solvents being used include butane, propane, isopropyl
alcohol, ethyl alcohol, and naphtha to name a small handful. Each of these
solvents has a Material Safety Data Sheet available online which discusses the
health hazards and common uses of each product. While many of these more
commonly used toxic substances are said to be purged or cleaned from the
products made with them, some chemical additives are included post production
to improve consumer ease of use. One of these substances is propylene glycol.

Propylene glycol caught my attention when I was
approached by a medicinal cannabis patient who asked if I had heard about
people getting lung polyps from smoking the vapor pen cartridges containing
this substance. Alarmed, I decided to do some research. This is what I found.

Propylene glycol
is a common and controversial chemical additive used in numerous industrial, pharmaceutical,
cosmetic and food products. Propylene glycol is also known by a number of other
chemical names depending on the formulation. Other names include 1,2
propanediol, 1,2 dihydroxypropane, methyl glycol, propane-1,2-diol and
trimethyl glycol. Propylene glycol is a nearly odorless, colorless liquid that
is used in e-cigarettes and cannabis vapor pen cartridges. It is used to improve
the flow or viscosity of the oil or substance and to act as a vaporous solvent
carrier for the substance in the cartridge. Propylene glycol is a stable liquid
at room temperature that vaporizes when heated.

Propylene glycol is used in so many products due to its
ability to absorb excess water while still maintaining consistent moisture
content in the product. This is an extremely useful property for a number of
reasons. Propylene glycol is used to make de-icing solutions for airplanes, to
make polyester compounds, to make plastics and paint and to create the
artificial smoke or fog used in theatrical productions and fire fighter
training. It has replaced ethylene glycol in the manufacture of anti-freeze as
it is less toxic if exposure or accidental ingestion occurs. It is also used as
an additive in numerous pharmaceutical medications.

Propylene glycol is also found in animal and human food
products and this is where the main controversy lies. While the US Food and
Drug Administration (FDA) has classified it as “generally recognized as safe”
for use in food products, it is limited to mainly non-food uses in Europe where
authorities are more cautious regarding what is allowed in foods and cosmetics.
The US Agency for Toxic Substances and Disease Registry contains comprehensive
information derived from compiled research studies done on animals and humans.
While they state that the toxicity level of propylene glycol is low, research
studies found in the Toxicology addendum show a number of demonstrated adverse
health effects in both animals and humans. Adverse effects have been shown to
effect the respiratory tract (from nose to lungs), the skin, and the kidneys in
mice, rats, cats, dogs, rabbits and humans.

Studies done on humans revealed that propylene glycol
causes mucus membrane irritation, skin sensitization and skin rashes. Since I
think of the interior of the lungs as a very super sensitive thin layer of
skin, which is exposed to the elements of the outside world with every
inspiration and intake of air and protected by numerous organs of filtration,
this is a concern. Higher doses of propylene glycol have been shown to lead to
hyperosmotic changes in the body, meaning it effects how water moves in and out
of cells and tissue spaces. Studies have shown a decrease in red blood cell
volume and health post propylene glycol ingestion.  It has been removed by the FDA as an ingredient
in cat food as it causes Heinz body anemia in cats. The Heinz bodies are found
in the red blood cells and indicate damage done to the hemoglobin. This renders
the red blood cells less able to carry oxygen. Decreased red blood cell volume,
decreased hemoglobin carrying capacity and decreased life span of the red blood
cell results, leading to anemia.

Propylene glycol has also been found to affect the
Central Nervous System at higher doses by causing a metabolic acidosis,
resulting from lactic acid buildup. Coupled with the reduced oxygen carrying
capacity of the red blood cells and resulting anemia, concerns arise regarding
nutrition to the brain, heart and other organs.

Looking to the research done by E-cig manufacturers, the
studies show very little to no harm caused by propylene glycol. These are also
the same people that manufacture and distribute tobacco cigarettes.

Many shampoos, lotions, deodorants and other products
used on the skin are now removing the propylene glycol due to skin irritation.
If you are inhaling or ingesting a product made with propylene glycol and are
experiencing symptoms of lung irritation, please consider the above
information. Be well.