What is really in vape aerosol?

Aerosol, not vapour

The cloud produced by an e-cigarette is an aerosol: a suspension of tiny liquid droplets and fine particles created when the device heats e-liquid. Calling it "vapour" makes it sound like harmless steam, but steam is simply water. Vape aerosol contains a range of substances, many of which are not meant to be inhaled.

The main ingredients

Most e-liquids are built from a handful of base components:

• Propylene glycol (PG) and vegetable glycerine (VG). These carrier liquids create the visible cloud. They are considered safe to eat, but "safe to eat" is not the same as "safe to heat and inhale repeatedly."
• Nicotine. Present in most products, often at high concentrations in a smooth "salt" form.
• Flavourings. Food-grade flavour chemicals designed for eating, whose effects when heated and inhaled are far less understood.

What forms when the liquid is heated

Heating changes chemistry. When e-liquid is vaporised, especially at higher temperatures or with certain devices, new compounds can form that were not in the bottle:

• Carbonyl compounds such as formaldehyde and acetaldehyde — known irritants, some classified as carcinogens.
• Volatile organic compounds that can irritate the airways.
• Ultrafine particles small enough to travel deep into the lungs and potentially into the bloodstream.

The flavour problem

Flavour chemicals are a particular area of concern. A compound may be perfectly safe to eat in a food product yet behave very differently when heated and drawn into the lungs. For example, certain buttery flavouring chemicals have been linked to serious lung disease in occupational settings. Because there are thousands of flavour combinations on the market, the inhalation safety of most has simply not been established.

Being approved as a food ingredient tells us nothing about whether a chemical is safe to vaporise and breathe in hundreds of times a day.

Why "we don't know" is itself a warning

The variety of devices, liquids and flavours — and the speed at which they change — means researchers are constantly playing catch-up. When a product is new and its contents are inconsistent, the absence of proven long-term harm should not be mistaken for proof of safety. History with tobacco shows how long serious harms can take to become fully visible.

The bottom line

Vape aerosol is not water. It is a heated chemical mixture containing nicotine, reaction by-products, ultrafine particles and sometimes metals. Inhaling it is not risk-free, and the safest choice — particularly for anyone who does not already vape — is not to start.