Vape Juice Ingredients Decoded – What PG, VG, Flavourings and Nicotine Actually Do Inside Your Device
Pick up any bottle of e-liquid from a legitimate retailer in Ireland and you will find, as required by law, a list of ingredients on the label. For many vapers, this list — propylene glycol, vegetable glycerin, flavourings, nicotine — is familiar but poorly understood. They know what vaping feels like, they know which flavours they enjoy, but the relationship between the liquid in the bottle and the experience it produces is often opaque. This gap in understanding has practical consequences: it means vapers often cannot troubleshoot problems effectively, cannot make informed choices between products, and sometimes carry unnecessary misconceptions about what they are inhaling.
This guide explains exactly what each component of e-liquid does, how the ratio between them affects your experience, and what the available evidence says about their safety in inhaled form.
Propylene Glycol (PG) – The Throat Hit Carrier
Propylene glycol is a synthetic organic compound that has been approved for use in food, pharmaceuticals, and cosmetics by health authorities worldwide for decades. It is used in a remarkable range of consumer products — as a humectant in food processing, as a solvent in pharmaceutical injectables, and as the base for many theatrical fog machines (which is relevant because the safety of inhaled PG aerosol has been studied in exactly this context).
In e-liquid, PG serves several functions simultaneously. It is a thin liquid that carries flavour compounds well and disperses them evenly through the finished product. It is responsible for the throat hit — the slight scratching sensation at the back of the throat on inhaling — because at the concentrations used in e-liquid, PG vapour creates a mild irritant effect that many ex-smokers find familiar and satisfying. And it is a humectant, meaning it draws moisture from surrounding tissues — which is the primary cause of the dry mouth many vapers experience.
PG is more mobile than VG, meaning it wicks through cotton more easily and suits tighter coil designs. This is why high-PG liquids (50/50 and above) are preferred in MTL devices with above-ohm coils, while sub-ohm devices tend to use lower-PG, higher-VG formulations where the viscosity of VG is less of a wicking concern.
Vegetable Glycerin (VG) – The Cloud Builder
Vegetable glycerin is a natural compound derived from plant oils, most commonly soybean, palm, or coconut oil. Like PG, it has a long history of safe use in food and pharmaceutical applications. Its properties in e-liquid are essentially complementary to those of PG: where PG is thin and produces a pronounced throat hit, VG is thick and produces dense, smooth vapour with minimal throat sensation.
The viscosity of VG is both its primary advantage and its main limitation. High-VG liquids — 70% VG and above, commonly used in sub-ohm devices — produce the large, dense vapour clouds associated with cloud chasing and with the most visually impressive aspects of vaping. The smooth texture of VG vapour means that high-VG liquids at low nicotine concentrations can be vaped in significant volume without harshness. But the thickness of VG creates wicking challenges in devices with fine cotton channels — the liquid moves slowly through the cotton, and at high wattage, the coil can outpace the wick and produce dry hits.
VG is also slightly sweet, contributing a background sweetness to e-liquid flavour profiles that is usually desirable in fruit and dessert liquids but can conflict with tobacco profiles trying to achieve a dryer, more austere character. Some premium tobacco e-liquids deliberately use higher PG ratios to achieve a drier mouthfeel.
Nicotine – The Pharmacologically Active Component
Nicotine is the pharmacologically active component of e-liquid — the compound responsible for the addictive properties of tobacco products and the satisfying effect that drives continued use among ex-smokers. It is a naturally occurring alkaloid found in the nightshade plant family, of which tobacco is one member. Nicotine itself is not a carcinogen and is not primarily responsible for the health harms of cigarette smoking — these arise primarily from combustion products, tar, and the hundreds of toxic and carcinogenic compounds produced when tobacco burns.
In e-liquid, nicotine is pharmaceutical-grade — extracted, purified, and standardised to a consistent concentration. Under Irish TPD regulations, the maximum permitted concentration in nicotine-containing e-liquid is 20mg per ml in 10ml bottles. Nicotine is present in two main forms in commercial e-liquid: freebase nicotine and nicotine salts, each with different absorption characteristics as discussed in detail elsewhere.
The effects of long-term nicotine inhalation via vaping — as distinct from the effects of tobacco smoking — are not fully established because vaping as a widespread practice is relatively recent. Current research does not indicate that nicotine per se, at the concentrations used in e-liquid, causes cancer or major organ damage, though its cardiovascular effects — vasoconstriction, increased heart rate and blood pressure — are well-documented and relevant for people with existing cardiovascular conditions.
Flavour Concentrates – The Complex Middle
Flavour concentrates are the most varied and least standardised component of e-liquid. A single e-liquid flavour profile may contain anywhere from a handful to dozens of individual flavour chemicals, most of which are drawn from the same ingredient palette used in food flavouring. The vast majority of these compounds have extensive safety records in food applications — but food safety data applies to ingested compounds, not inhaled aerosols.
The distinction matters. Several flavouring compounds that are perfectly safe when eaten have been identified as potentially problematic when inhaled. The most notable historical case is diacetyl — a butter-flavouring compound that was used in early e-liquids and has been linked to a rare but serious lung condition called bronchiolitis obliterans when inhaled in occupational settings. Reputable e-liquid manufacturers removed diacetyl from their products years ago, and it is not present in products from established brands currently sold in Ireland.
The ongoing research challenge is that the inhalation safety of flavouring compounds generally is not well-established for chronic, repeated exposure. Responsible manufacturers in the industry have made significant investments in safety testing of their flavour formulations, and products registered with the HPRA in Ireland have undergone a notification process that includes ingredient disclosure. The most prudent approach for consumers is to purchase from established brands with transparent ingredient lists rather than from unverified sources.
Water and Other Additives
Some e-liquids contain small amounts of water, typically to adjust viscosity or to aid in the dissolution of certain flavour concentrates. Water is inert and safe, though its presence in significant quantities can affect vapour temperature and coil performance. Most quality e-liquids contain water only at trace levels if at all.
Other additives found in some e-liquids include ethyl alcohol (a solvent used in some flavour concentrates and present at very low levels in finished products), citric acid or other pH adjusters (used primarily in nic salt formulations), and various preservatives or antioxidants added to extend shelf life. The ingredient list on TPD-compliant products must disclose all of these components, providing consumers with the information they need to make informed choices.
Interpreting PG/VG Ratios on Labels
E-liquid labels typically express the PG/VG ratio as two numbers separated by a slash — for example, 50/50, 70VG/30PG, or 80VG/20PG. The first number is PG, the second VG, unless explicitly labelled otherwise. Higher PG ratios give a stronger throat hit, lower vapour production, and better wicking in tight coils. Higher VG ratios give smoother vapour, larger clouds, and require more open coil designs to wick efficiently.
For MTL vapers using pod systems or pen-style devices with above-ohm coils, 50/50 or high-PG liquids (up to 70PG/30VG) work best. For sub-ohm devices, 70VG/30PG or higher is standard. Using a high-VG liquid in an MTL device will cause wicking problems and potentially damage the coil; using a high-PG liquid in a sub-ohm device will produce insufficient vapour and may affect the coil differently than intended.
The ratio printed on the label is determined at manufacture and does not change in the bottle. Some vapers mix liquids of different ratios to achieve a custom blend, and this is perfectly safe as long as the resulting nicotine concentration is calculated correctly. For most vapers, choosing the appropriate pre-mixed ratio for their device is the simpler and more reliable approach.
