What Ingredients Are Commonly Used in Vape Liquids?

Propylene Glycol (PG)

What it is: A synthetic alcohol compound (a diol) produced from petroleum or biological sources. PG is classified as Generally Recognised as Safe (GRAS) by the FDA for food use and is widely used in food production, pharmaceutical formulations, cosmetics and asthma inhalers.

Role in e-liquid: PG is the primary carrier for nicotine and flavourings because it dissolves them efficiently and carries their taste effectively. It produces the throat hit — the sensation at the back of the throat on inhalation — that many vapers find satisfying as an analogue to cigarette smoke. PG produces thinner vapour than VG.

Safety: PG is well studied in oral and pharmaceutical inhalation contexts. Long-term inhalation data specifically for vaping is more limited but the compound is considered low-toxicity. Its main practical side effect for vapers is dehydration — PG is hygroscopic and draws moisture from oral and respiratory mucous membranes, which can cause dry mouth, throat irritation and systemic mild dehydration if water intake is not increased. A small minority of people have a sensitivity or allergy to PG and should use high-VG or VG-only liquids.

Vegetable Glycerin (VG)

What it is: A natural compound derived from plant oils — most commonly palm, soy or coconut oil — through a hydrolysis process. VG is classified as GRAS, is widely used as a food sweetener and humectant, and appears in many cosmetics and pharmaceutical products.

Role in e-liquid: VG is the primary vapour-producing ingredient — it creates the dense, visible clouds associated with vaping. It adds a slight natural sweetness to liquids and produces a smoother, less harsh inhale than PG. Higher VG ratios (70% and above) reduce throat hit and increase vapour density, making them popular for sub-ohm and direct-to-lung vaping styles.

Safety: VG has an excellent safety profile in food and pharmaceutical use. Inhalation-specific studies suggest it is well tolerated by most people. VG does not cause the dehydration associated with PG, making high-VG liquids a better option for vapers who experience dry mouth or throat sensitivity on standard ratio liquids.

Nicotine — Freebase and Nicotine Salts

What it is: A naturally occurring alkaloid found primarily in the tobacco plant. Nicotine in e-liquids is extracted and purified from tobacco leaf, then added to the PG/VG carrier in precise concentrations.

Freebase nicotine: The standard form used in most e-liquids below 20mg/ml. Freebase nicotine has a higher pH, produces a stronger throat hit at higher concentrations and is absorbed slightly more slowly than nicotine salts.

Nicotine salts: Nicotine combined with an organic acid (typically benzoic acid) to create a lower pH salt form. Nicotine salts deliver nicotine more smoothly and rapidly, allowing higher concentrations (10–20mg/ml) to be used without the harsh throat hit of equivalent freebase concentrations. This makes them the preferred format for the compact pod devices designed to replace cigarettes.

Safety: Nicotine itself has well-documented effects on the cardiovascular system, brain and reproductive biology — covered in detail in our separate guide on what nicotine does to your body. Maximum UK concentration is 20mg/ml.

Food-Grade Flavouring Concentrates

What they are: The flavour compounds in e-liquids are typically food-grade concentrates derived from natural and artificial flavouring substances. The same classes of flavouring compounds used in food manufacture are used in e-liquids, though they are inhaled rather than ingested — a distinction that matters for safety assessment.

Role in e-liquid: Flavourings account for approximately 1–10% of an e-liquid formulation by volume and are responsible for the entire flavour profile — from tobacco and menthol through to fruit, dessert and drink profiles. They are the most variable component between different products and are the primary source of inter-product differences in vapour character.

Safety: The inhalation safety of flavouring compounds is the least settled area of e-liquid science. Many flavouring compounds are GRAS for food use but food safety and inhalation safety are different assessments — the respiratory tract absorbs compounds differently to the gut. UK TRPR bans diacetyl and acetyl propionyl (the compounds linked to popcorn lung) and requires that flavouring ingredients do not present a risk to human health. Research on specific flavouring compounds and their inhalation profiles is ongoing.

Distilled Water (where added)

What it is: Purified water, added in small quantities in some formulations.

Role in e-liquid: Water reduces the viscosity of high-VG liquids, improving wicking in certain coil types and producing a slightly cooler, thinner vapour. It is not present in all formulations and is typically used at concentrations of 1–5% where it appears.

Safety: Distilled water in small concentrations presents no safety concern.