Propylene glycol and vegetable glycerin, known as PG and VG, are the two primary ingredients in e-liquid and the resulting vapor.

Propylene Glycol (PG)

PG has the chemical name 1,2-propanediol, and is a generally recognized as safe chemical that is used in a wide range of consumer products, including pharmaceuticals, sunscreen, lotions, shampoos, food flavorings, pet foods, cosmetic creams, theatrical smoke machines and many more products. PG is also used in anti-freeze, but it’s used to make the anti-freeze drastically less toxic for humans and pets. In e-liquid, food grade PG is used to carry the flavor, and the fact that it’s slightly irritating to the throat when inhaled means that it contributes to the “throat hit” of the vapor.

Vegetable Glycerin (VG)

VG has the chemical name 1,2,3-propanetriol, and like PG, is a generally recognized as safe chemical used in a multitude of consumer products, including pharmaceuticals, foods, cosmetics and in tobacco. As with PG, it may be irritating when inhaled. However, in e-liquid VG produces a much smoother throat-hit, is thicker than PG and imparts more sweetness to the taste.

Safety of PG and VG for Inhalation

There is limited evidence on the safety of PG and VG for inhalation, but studies on those exposed to theatrical fog machines (which also use other chemicals as well as lower-grade PG) generally show very little evidence of harm, with irritation being the only notable effect. Animal studies on PG and VG have also shown no evidence of harm other than mild irritation. However, more research is needed to make any definitive statements about their risks for vapers.

PG/VG Ratios in E-Liquid

The most important thing about PG and VG for vapers is the relative quantities of them used in a given e-liquid. Generally speaking, higher PG levels improve the flavor (because it doesn’t drown it out as much as VG), produce a stronger throat hit and make the liquid thinner (and therefore more efficient at wicking). On the other hand, VG-based liquids produce thicker vapor, but are more viscous, so they won’t wick as effectively.

At Black Note, we use a 50/50 mix of PG and VG, which provides a nice balance between throat-hit, flavor and vapor production.