What Is in E-Liquid? Ingredients, Aerosol and Health Evidence

Propylene glycol, or PG, is a relatively low-viscosity carrier. Vegetable glycerine, or VG, is more viscous and is also called glycerol. Their ratio affects liquid flow, wicking, aerosol production, and sensory qualities. A balanced liquid commonly suits a small pod, while a VG-led liquid commonly suits larger wicking ports and higher output. Device guidance matters more than a general rule.

Water or ethanol can be present to adjust formulation properties. Nicotine salt liquids normally combine nicotine with an acid, but salt is a broad formulation category rather than one chemical recipe. Flavour concentrates can include multiple aromatic compounds, and producers may also use sweetening or cooling constituents. UK consumer rules ban certain ingredients in nicotine products, including colourings, caffeine, and taurine, but the absence of those ingredients does not turn the remainder into an inhalation guarantee.

The useful question is therefore not how many ingredients all vapes have. It is what the exact product contains, whether that product is legally supplied, how it is used, and what the evidence can show about the resulting aerosol and exposure.

Nicotine is optional in e-liquid. When present, the label concentration in mg/ml describes the amount in each millilitre of liquid, not the amount absorbed from one draw. Delivery varies with formulation, device, power, puffing, experience, and how often the product is used. Read the nicotine content guide before comparing labels.

Nicotine is addictive and can be harmful in high doses. It is not, however, the main source of the cancer, lung, and cardiovascular burden caused by smoking. Cigarettes burn tobacco and produce a complex smoke containing tar, carbon monoxide, and many toxic chemicals. Vapes do not burn tobacco, which is central to their lower-risk role for adults who would otherwise smoke.

This distinction must not become an endorsement for new use. Children, young people, and people who do not smoke should not vape. During pregnancy, the NHS recommends licensed nicotine replacement products and advice from a GP. Liquid nicotine must be kept away from children and pets, and spills should be handled using the product instructions.

Heating does not simply lift an unchanged liquid into the air. Some liquid becomes aerosol droplets, while heat can also break down or transform constituents. MHRA guidance for products seeking a medicine licence identifies acrolein, formaldehyde, and acetaldehyde as carbonyls that can form through thermal decomposition of glycerol or propylene glycol under some conditions. It also calls for examination of particles and metals that can come from heating elements, solder, adhesives, plastics, and other components.

That medicine-licensing guidance sets a higher evidence pathway than ordinary consumer notification. It is useful here because it shows the chemical questions a rigorous product assessment must ask. It does not mean that every consumer product produces the same compounds at the same level or has completed medicinal testing.

Power, temperature control, airflow, liquid supply to the wick, coil age, deposits, and draw pattern can change emissions. A dry or burnt draw signals a problem, not a normal flavour to push through. Stop, let the device cool, check liquid level and compatibility, replace a spent pod or coil, and follow the manufacturer instructions. Do not modify power beyond the supported range or improvise liquid ingredients.