If you've spent any time around vaping, you'll have heard "PG" thrown about to describe e-liquid. It's short for propylene glycol, one of the two main liquids that make up the base of pretty much every e-liquid on the shelf, the other being vegetable glycerin (VG). Both are widely used and well established across the food, drink and cosmetics industries, and altering the ratio between them is what changes an e-liquid's thickness and the kind of vape it produces.

'Classic' e-liquids lean more heavily on PG than VG, which gives a thinner consistency and the sharper 'throat hit' that a lot of smokers compare to a cigarette. That's why classic liquids tend to suit people switching over from smoking with a low-wattage Pen-Style Kit, rather than jumping straight into a big cloud-chasing setup.

'Sub ohm' liquids, on the other hand, carry more VG than PG. Since VG is naturally thicker, these liquids are built for high-wattage sub ohm devices designed to produce plenty of vapour and bold flavour.

So what exactly is propylene glycol, and where else do you come across it?

What is propylene glycol used for?

Propylene glycol is a synthetic liquid additive used across food, drink and cosmetic products for a handful of practical jobs. It's odourless, colourless and has almost no taste of its own.

It dissolves certain substances more effectively than water and holds onto moisture well, which is why it's such a common ingredient in processed food: it helps stop things drying out. Some of its other jobs in food, drink and cosmetic products:

• Anti-caking: stops foods sticking together.
• Antioxidant: helps extend shelf life by protecting against oxidation.
• Emulsifier: keeps ingredients blended that would otherwise separate.
• Moisture retention: stops food drying out.
• Texture and thickness: adds body to certain products.
• Carrier substance: helps other additives, such as colours and flavourings, mix through evenly.
• Appearance: makes certain foods or drinks look clearer or more vibrant.

Beyond food, PG turns up in a wide range of injectable medications, topical creams and ointments, and everyday personal care and cosmetic products. In the UK, propylene glycol (listed as E1520) is an authorised food additive, and it's been used across these industries for decades.

Is propylene glycol safe?

Propylene glycol carries a low toxicity rating, and its approval as a UK food additive reflects that. Eating something and inhaling it as vapour aren't automatically the same thing, though, and that's one of the areas ongoing UK research into vaping keeps an eye on. The government's independent evidence review into vaping tracks ingredient and health research as part of its ongoing monitoring, and Cancer Research UK is clear that there's currently no good evidence that vaping itself causes cancer, while also being upfront that vaping isn't completely risk-free and its long-term effects aren't fully understood yet.

Under the Tobacco and Related Products Regulations 2016, any nicotine-containing e-liquid sold in the UK has to use ingredients that don't pose a risk to human health, heated or unheated, and a small list of substances (including diacetyl) is banned outright. That regulatory backstop applies whatever the PG/VG ratio.

Propylene glycol vs vegetable glycerin: what's actually different

PG and VG do the same broad job (carrying flavour and, where used, nicotine) but behave quite differently in a tank or pod:

• Consistency: PG is thin and watery. VG is thicker and stickier, closer to syrup.
• Throat hit: PG produces a sharper, more pronounced throat hit, similar to the sensation of smoking. VG feels smoother and softer.
• Vapour production: VG produces noticeably more vapour. PG produces very little on its own.
• Flavour: PG carries flavouring crisply and true to taste. VG rounds flavours off slightly and adds a subtle natural sweetness of its own.
• Device wear: higher-VG liquids are thicker and can gunge up coils and wicks faster in low-wattage devices not built for them, which is why sub ohm tanks use different coils to pen-style kits.

Most bottled e-liquid sits somewhere on a spectrum between the two, commonly 50/50, 60/40 or higher-VG blends for sub ohm setups. There's no universally "better" ratio: it comes down to the kit being used and the kind of vape someone's after.

Can you be allergic to propylene glycol?

A small number of vapers report irritation, such as a dry throat, cough or mild skin reaction, that they put down to PG. It isn't always straightforward to pin down, since dry hits, a new coil "breaking in," or simply switching flavours can cause similar symptoms.

If you notice ongoing irritation that doesn't settle down, the sensible move is to see a GP rather than self-diagnose, particularly if symptoms are severe or persistent. Since manufacturers are required under UK regulation to ensure e-liquid ingredients don't pose a risk to health, switching to a higher-VG or PG-free e-liquid is a reasonable next step to try if PG is suspected, though results vary from person to person.

Propylene glycol and antifreeze

Vaping comes with its fair share of myths, and one that won't go away is the link between PG and antifreeze, a liquid added to a car radiator to stop the water inside freezing.

That link exists because propylene glycol is often mixed up with ethylene glycol, a genuinely toxic substance that isn't safe for human consumption and has no place in food, cosmetics or medicine. Ethylene glycol poisoning is a real medical emergency that can affect the kidneys and, in serious cases, be fatal.

Propylene glycol and ethylene glycol are both used in some antifreeze formulations because they share a low freezing point, but that's about as far as the similarity goes. They're chemically distinct substances with very different safety profiles, and PG's presence in an antifreeze bottle on a supermarket shelf doesn't say anything about its safety when used in food, cosmetics or e-liquid.

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