Quick summary: A scientific review of indoor air quality data has confirmed that vaping creates a 99% reduction in toxicants compared to traditional cigarette smoke, with exhaled liquid aerosol droplets evaporating within seconds rather than lingering for an hour. Despite these profound chemical differences, public policy trends across the UK and the European Union increasingly treat vaping identically to smoking by imposing strict de facto or legal bans in public spaces and workplaces. For public healthcare practice and smoker well-being, experts warn that forcing adult vapers into designated smoking zones threatens their mental health and risks triggering a smoking relapse, which severely undermines global tobacco harm reduction goals.
The chemical breakdown of vape aerosol, and therefore the harm potential of using vapes indoors, is not widely understood by consumers or regulators. To help address this, Matt Stevenson, Scientific Substantiation Senior Manager at Imperial Brands, explores what the weight of scientific evidence says.
Cigarette smoke and vape aerosol are fundamentally different, and this needs to be considered when attempting to compare the two. Cigarette smoke is the product of tobacco combustion. Burning tobacco generates over 7,000 chemicals, over 70 of which are defined as harmful or potentially harmful to health by leading regulatory authorities like the US FDA.
By contrast, vapes do not contain tobacco. Their aerosol is chemically much simpler, consisting primarily of tiny liquid droplets containing Propylene Glycol (PG), Vegetable Glycerine (VG), nicotine (if present), and flavouring chemicals. Focusing on potentially harmful chemicals, there is up to a 99% reduction in toxicants in vape aerosol compared to cigarette smoke.
A cigarette will smoulder between puffs, releasing sidestream, or second-hand, smoke. Vapes do not smoulder; aerosol is only generated through either pressing a button or puffing on a device, meaning the only way vape aerosol is released into the air is through user exhalation, minimising impact on bystanders. These exhaled droplets, made up of water, PG, and VG, evaporate or dissipate within seconds of a vaper exhaling, whereas particles generated by cigarette smoke can linger in the air for up to an hour depending on room conditions.
Neither cigarette smoke nor vape aerosol consists of a single particle type. Both are mixtures of particles known as Particulate Matter (PM), which can come from many sources beyond smoking, including petrol or diesel vehicles, forest fires, industrial emissions, and natural sources such as pollen and dust.
For regulatory purposes, these particles are classified by diameter. Those measuring 10 microns or less (PM10) are inhalable into the upper region of the lungs, while those measuring 2.5 microns or less (PM2.5) can reach deep into the lungs. The PM generated from cigarette smoke is a complex mixture of liquid droplets and solid carbon-based particles, whereas vape particles consist solely of liquid droplets containing water, PG, and VG. This distinction underscores why particles, including PM, need to be robustly chemically characterised in order to fully understand any potential risks arising from their presence.
Impact on Indoor Air Quality (IAQ) is an important public health consideration for inhaled Next-Generation Products (NGP), and a wealth of research exists in this area for vape and heated tobacco products. Studies have demonstrated that vaping indoors does not release chemicals or toxins into the air at levels that would pose air quality issues to bystanders when measured against established IAQ regulations and guidelines, with significant reductions in toxicant levels found relative to cigarette smoke.
There are limitations to this research, however. One issue is the absence of official standardised testing procedures, meaning different research groups often use different methods and can reach differing conclusions. Some studies use test rooms with controlled environmental conditions to limit the impact of external influences, an approach that may not always reflect real-world use. Real-world studies, meanwhile, can suffer from a lack of controlled conditions, such as weather, number of participants, or fragrances participants may be wearing, which can also skew results.
Indoor vaping rules across the EU and the UK reflect a shared trend toward treating vaping similarly to smoking in public spaces, though the legal structures differ.
At the EU level, the Tobacco Products Directive (TPD) imposes product safety standards, including nicotine limits, tank and bottle size caps, and mandatory warnings, but leaves decisions about indoor use to individual member states, resulting in widely varying policies. Countries including Italy and Spain prohibit vaping in indoor public spaces such as bars, restaurants, and public transport, with fines for violations. Hungary enforces some of the strictest rules, banning vaping wherever smoking is banned and issuing significant financial penalties. Portugal and others follow similar patterns, restricting vaping in enclosed public areas and child-focused spaces like schools and playgrounds. European governments justify these restrictions on several grounds, including protecting the public from exposure to aerosol, maintaining clear and enforceable public space rules, and preventing youth uptake amid rising concerns about flavoured products and disposable devices.
The UK retains TPD-style product rules through its post-Brexit TPD Regulations framework, but does not currently impose a national ban on indoor vaping. Instead, indoor use policies are set by businesses, workplaces, and transport operators. In practice, most public houses, restaurants, and public transport services prohibit indoor vaping, with many pubs citing difficulties distinguishing vaping from smoking, the need to maintain customer comfort, and the desire to uphold family-friendly environments. Although these restrictions are not mandated by law, they function as de facto indoor bans across much of public life.
It is crucial, however, that adults who have switched to NGP are not forced into smoking areas in workplaces or outdoors, as this contradicts previous efforts to prevent the normalisation of smoking and may inadvertently facilitate smoking relapse, which would greatly weaken the potential of NGP to positively contribute to tobacco harm reduction goals.