What is PG (propylene glycol)?

What PG actually is

Propylene glycol is a clear, almost odourless, slightly sweet but mostly tasteless liquid produced from petroleum or sometimes plant oils. It is one of the most widely used compounds in food, cosmetics, pharmaceuticals and industry. The pharmaceutical grade (USP or BP grade) is the standard for e-liquid manufacturing.

• Chemical name: Propane-1,2-diol (C3H8O2). A simple diol compound.
• Source: Mostly petrochemical production. Bio-based PG made from glycerol or biomass is also available.
• Grade for vaping: USP (US Pharmacopeia) or BP (British Pharmacopoeia) grade. Highest purity. Not the same as automotive antifreeze (different grade and additives).
• Where else you find it: Asthma inhalers and nebulisers (carrier for medication), ice cream and processed foods (humectant), fog machines in theatres, cosmetics, medicine, even some skincare.
• Important note about antifreeze: Yes, PG is used in some antifreeze. The key word is “some”. Automotive antifreeze typically uses ethylene glycol (toxic) or PG with anti-corrosion additives (also toxic). Pure pharmaceutical-grade PG used in e-liquid is a completely different product, just like the difference between table salt and rock salt for highways.

How PG behaves in vape juice

The PG sensitivity question

PG sensitivity is the most common reason vapers switch to higher-VG ratios. It is more common than VG sensitivity, though still relatively rare overall.

PG sensitivity is real but not allergic in most cases. Most reactions are irritation rather than true allergy. Some people simply tolerate PG less well than others, especially in higher ratios.

• Common symptoms: Dry mouth, sore throat, mild headache, throat irritation, occasional skin rash.
• How common: Estimated 5-10% of vapers experience some PG sensitivity. True allergic reactions are much rarer.
• What to try first: Switch to a higher VG ratio. 70VG/30PG or higher. Symptoms often resolve quickly.
• If symptoms persist with high-VG: Could be other irritants in e-liquid (sweeteners, flavourings) rather than PG itself. Try simpler, less-sweetened flavours.
• For complete PG avoidance: Max-VG (100% VG) liquids exist. Limited range. Specialist shops or online retailers stock them.
• True PG allergy: Very rare. Symptoms can include severe skin reactions, breathing difficulties. Stop vaping immediately and see a GP.

PG percentages explained

E-liquid labels show VG/PG ratios. The second number is PG percentage. Higher PG means more throat hit, more flavour, less cloud production.

PG and nicotine delivery

PG affects how nicotine feels and how it is delivered. Worth understanding if you are adjusting your nicotine experience.

• Throat hit: PG amplifies the throat hit of nicotine. The same 10mg nicotine feels stronger in 50PG/50VG than in 70VG/30PG.
• Speed of delivery: PG vapourises at lower temperatures than VG. Nicotine carried in PG-heavy liquid can feel slightly faster.
• Nicotine salts: Designed to deliver fast without harsh throat hit even at high strengths. Pair best with 50PG/50VG balanced ratios.
• Freebase nicotine: The traditional form. Stronger throat hit. Suits both PG-heavy and VG-heavy ratios but feels different in each.

PG safety

PG has decades of safety data from food, cosmetics, medicine and inhalation use (asthma inhalers contain PG). The specific question of vapourised PG is newer but well-studied relative to most consumer chemicals.

• FDA GRAS status: US FDA classifies PG as Generally Recognised As Safe for food use.
• EMA approval: European Medicines Agency approves PG for use in medicines including inhalers and nebulisers.
• WHO classification: Listed as “Generally regarded as safe.”
• Inhalation safety: PG has been inhaled in asthma medication for decades. Used in fog machines in entertainment industry for similar timeframe with no significant safety issues identified.
• Royal College of Physicians and NHS position: Vaping (which includes PG) is considered substantially less harmful than smoking. Current best estimate is around 95% reduction in harm.
• Long-term effects: Still being researched as vaping has only existed at scale for around 15 years. No major safety signals have emerged.

The bottom line