If you’ve ever looked closely at an e-liquid bottle, you’ve probably noticed propylene glycol listed as one of the main ingredients. Often shortened to PG, it’s the quiet workhorse in your vape — delivering flavour, enhancing throat hit, and balancing the mix with vegetable glycerine. But here’s where things get interesting: not all PG is the same, and when it comes to inhalation safety, the type used matters more than most vapers realise.
This article examines the various types of propylene glycol used in vaping, their differences, and why pharmaceutical-grade PG is the only type that should ever reach your tank.
What is Propylene Glycol in Vaping?
Propylene glycol is a colourless, odourless liquid that’s used in everything from food flavourings to asthma inhalers. In vaping, PG works as a carrier, helping flavours blend smoothly while giving a satisfying throat sensation. It’s also thinner than VG, which makes it ideal for pod systems and flavour-forward mixes.
But behind the simplicity of this ingredient lies a crucial distinction: the grade of propylene glycol can determine whether it’s safe for inhalation, or more suited to antifreeze and paint thinners.
Breaking Down the Types of Propylene Glycol
There are four main types of PG you may come across, either in e-liquid manufacturing or on ingredient lists. Understanding the difference is crucial, especially for vapers who value quality and transparency.
Table: Types of Propylene Glycol and Their Key Differences
Both USP (United States Pharmacopeia) and EP (European Pharmacopoeia) grades meet extremely strict standards for purity and safety. These are the only two types of PG truly suitable for inhalation through vaping.
What Makes USP and EP Grade PG Safe?
USP and EP grade PG is produced under pharmaceutical-level conditions. The manufacturing process involves multiple stages of purification, including fractional distillation and filtration, to ensure no harmful impurities are left behind. Final batches are tested against stringent purity criteria and monitored for residual solvents, microbial contaminants and heavy metals.
Because of this, pharmaceutical-grade PG is used in products designed for the lungs, like medical nebulisers and inhalers, not just e-liquids.
When vapers talk about clean flavour, smooth delivery and predictable performance, USP and EP grade PG is what makes that possible.
Is Food Grade PG Safe for Vaping?
Here’s where things get murky. Food-grade propylene glycol might meet high standards for ingestion, but it’s not always batch-tested for inhalation. That means it can still contain trace impurities that wouldn’t be a problem in your mouth, but may be unsuitable for your lungs.
Addressing Common Questions Around Propylene Glycol
Is propylene glycol the same thing as antifreeze?
No. While PG is used in some non-toxic antifreeze blends, that refers to industrial-grade PG, not the pharmaceutical-grade used in e-liquids.
Is PG bad for you?
Inhalation safety largely depends on the grade and purity. USP/EP PG is recognised as safe for inhalation when used correctly. Industrial or technical grades should never be inhaled.
Can PG cause irritation?
Some people with sensitivities may notice dryness or a scratchy throat. Switching to a higher VG blend or ensuring the PG is USP grade often solves the issue.
The Standard Behind the Vapour
Not every e-liquid is created with the same attention to safety or sourcing. If you’re someone who wants to know precisely what you’re inhaling, it’s worth understanding the types of propylene glycol out there.