What Are E-Liquids? Technical Definition and Composition

E-liquids are formulated liquids designed to be aerosolised in electronic vaping devices. When heated, they generate an inhalable output without combustion. In regulatory and scientific terms, this output is a liquid-based aerosol, not a gas-phase vapour.

Technical clarification: The distinction between aerosol and vapour is critical for understanding particle size, delivery efficiency, and deposition behaviour in inhalation systems.

Core Functional Definition

From a technical standpoint, an e-liquid is a homogeneous liquid system composed of humectants, flavouring compounds, and optionally nicotine. Its primary functions are:

• Controlled aerosol generation (aerosolisation)
• Flavour transport via suspended liquid particles
• Optional nicotine delivery without combustion

Main Components of E-Liquids

Propylene Glycol (PG)

Propylene Glycol (E1520) is a low-viscosity humectant widely used in pharmaceutical formulations. In e-liquids, PG functions as:

• Primary flavour carrier
• Viscosity regulator
• Contributor to throat sensation

Hygroscopic property: PG attracts and binds water molecules from the surrounding environment. Prolonged air exposure can alter viscosity and wicking behaviour.

See also: VG/PG Base Ratios – Technical Overview

Vegetable Glycerin (VG)

Vegetable Glycerin (E422) is a high-viscosity, plant-derived humectant. Its technical roles include:

• Increasing aerosol density
• Softening perceived vapour texture
• Stabilising aerosol formation at higher power levels

Hygroscopic property: Like PG, VG absorbs moisture from air, which may influence long-term viscosity and storage stability.

PG vs VG — Technical Comparison

Flavouring Compounds

Flavourings are aromatic compounds, typically dissolved in PG. Modern formulations increasingly differentiate between:

• Food-grade flavourings (ingestion-oriented)
• Inhalation-considered flavour systems (screened for aerosol behaviour)

Nicotine (Optional)

Nicotine may be present in different chemical forms:

• Freebase nicotine – higher pH, stronger sensory impact
• Nicotine salts – stabilised forms with modified pH and volatility

EU and Irish regulations limit nicotine concentration to 20 mg/ml in products placed on the market.

Physical and Chemical Stability

Nicotine-containing e-liquids are sensitive to photo-oxidation and thermal degradation. Exposure to light, heat, and oxygen can accelerate chemical ageing.

Storage note: Proper storage in amber glass or opaque containers helps maintain chemical stability and slow oxidation.

Aerosolisation Process

During device operation, e-liquids undergo aerosolisation rather than combustion. This produces suspended liquid droplets carried in air.

• Coil temperature and surface area
• Wicking efficiency
• Liquid viscosity and saturation rate

Regulatory Classification (Ireland / EU)

E-liquids in Ireland are regulated under the Tobacco Products Directive (2014/40/EU) and national implementing legislation.

They are not classified as medicines or health products.

Frequently Asked Technical Questions

Is the output of an e-cigarette vapour?

No. Technically, it is a liquid-based aerosol, not a gas-phase vapour.

Why can e-liquids change colour over time?

Colour change is often associated with oxidation, particularly in nicotine-containing liquids exposed to light and oxygen.

Does PG or VG affect device compatibility?

Yes. VG/PG ratio directly affects viscosity and wicking behaviour and must match coil design.

Intent Disclosure

This page provides technical reference information only.