E-liquid, commonly called vape juice, is typically composed of four main ingredients: nicotine, flavorings, and two primary base solvents. These solvents are Propylene Glycol (PG) and Vegetable Glycerin (VG), which make up the vast majority of the liquid volume. PG is one of the two foundational components necessary for creating the aerosol, or vapor. This colorless, nearly odorless synthetic organic compound plays a specific role in the chemistry and user experience of vaping.
The Essential Function of Propylene Glycol in E-Liquids
Propylene glycol is included in e-liquid formulations primarily because of its superior ability to act as a carrier for flavor and nicotine molecules. Its chemical structure allows it to bind effectively with flavor concentrates, ensuring the taste is delivered clearly and intensely. High-PG liquids are often preferred by vapers who prioritize a vivid flavor profile over large vapor production.
PG also possesses low viscosity, meaning it is a thin liquid compared to vegetable glycerin. This low viscosity is important for the physical function of the vaping device. It allows the e-liquid to wick efficiently through the small channels of atomizers and coils, particularly in lower-powered devices. E-liquids with a higher PG content are less likely to clog or cause issues in smaller, mouth-to-lung style vaping systems.
A primary function of propylene glycol is its contribution to the physical sensation known as “throat hit.” This mild, slightly scratchy feeling at the back of the throat mimics the sensation of inhaling tobacco smoke. Increased PG concentration correlates with a stronger throat hit, offering a more assertive tactile experience for the user.
Comparing Propylene Glycol and Vegetable Glycerin
Propylene glycol and vegetable glycerin are the two primary components of e-liquid, and they are mixed together, with their ratio dictating the final product’s characteristics. VG is a natural compound derived from vegetable oils that is much thicker and more viscous than PG. This higher viscosity means VG is responsible for producing the dense clouds of vapor sought after by some users, a practice often called “cloud chasing.”
Vegetable glycerin also has a subtle, mildly sweet taste, which can affect the overall flavor profile. While PG is the superior flavor carrier, VG’s sweetness can enhance certain dessert or fruit flavors. The thickness of VG means it does not carry flavor as efficiently as PG, often requiring a higher concentration of flavorings to achieve the same intensity.
Manufacturers use specific PG/VG ratios to tailor the vaping experience. A balanced 50/50 ratio provides a good mix of throat hit, flavor, and moderate vapor production, working well in most standard devices. Conversely, a high-VG ratio, such as 70% VG and 30% PG, is favored for sub-ohm devices that operate at higher temperatures, prioritizing vapor output and a smoother throat feel.
Safety Profile of Inhaled Propylene Glycol
Propylene glycol is designated as Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration (FDA) for use in food, cosmetic, and pharmaceutical products, including ingestion and topical application. However, this GRAS status does not automatically extend to the repeated, long-term inhalation of aerosolized PG. The process of heating and inhaling PG is distinct from its use as a food additive.
When inhaled, PG can cause common, short-term side effects, primarily due to its humectant properties. Propylene glycol attracts and absorbs water molecules, which can lead to mild temporary dehydration and irritation of the mouth and throat tissues. Users may experience a dry mouth, a sore throat, or increased thirst, which are manageable by increasing water intake.
Scientific data regarding the long-term effects of inhaling PG is limited, as the practice of vaping is relatively new. Some studies suggest that exposure to PG aerosols at concentrations found in e-cigarettes may cause irritation to the eyes and throat in certain individuals. The toxicological profile for chronic inhalation in humans is still being evaluated.