There has been a recent resurgence in fearmongering propaganda about e-cigarette vapor exposing vapers and bystanders to “particles.” Anyone with a middle-school level understanding of science can see why this is nonsense. It is really quite simple: Inhaling some kinds of solid particles can cause harm, even when the chemicals in them are harmless, but nothing similar is true for the liquid droplets produced by e-cigarettes.
Size and shape matter for inhaled solids, which are called “particulate matter” in the context of air pollution. Asbestos is not chemically toxic – eating it is harmless – but some of the particles can lodge in the lung and cause disease because of their size and shape. Very small particles of soot that are created by combustion (often called “ultrafine particles” or “PM2.5”) can lodge in the lungs or pass through the lungs into the bloodstream. Because they remain solids, they can lodge elsewhere in the body causing harm.
Evidence suggests that these small particles are a particularly harmful component of air pollution (though the science there is far weaker than you might believe from reading newspaper accounts). Recent research suggests that much of the cardiovascular disease from smoking is caused by the deposition of small particles in blood vessels. Smoke, in contrast with vapor, contains solid particles.
The liquid droplets created by e-cigarettes have no fixed shape. Their size has some effects, but those are not similar to the effects of solids. Smaller droplets tend to reach lower into the lungs before depositing on a surface of the airway (which allows faster uptake of nicotine); larger droplets increase the local concentration of their chemicals when they land (which could be bad if the chemicals harmed tissue, but they do not). Liquid droplets cannot lodge in the lungs or anywhere else. They dissolve into the bloodstream and the body’s other liquids. Only their total volume affects what is then in the body; their original size and shape does not matter at all.
The conflation of droplets with actual particulate matter and its harmful properties seems to trace back to gross negligence rather than malice. Researchers whose favorite equipment cannot detect the difference between liquids in solids in aerosols mistakenly reported seeing “particulates” in the vapor. (E-cigarette “vapor” is really mostly an aerosol, not technically vapor.) Users of such equipment tend to refer to both particles and droplets as “particles” because both look the same to them. That does not cause much trouble until they port this language, and their inability to distinguish, to a health context. There it is extremely misleading.
But the real problem was created by anti-vaping activist and pseudo-scientist Stanton Glantz pushing the false message that droplets are particulate matter. This resulted in statements from him and his followers that falsely imply, and sometimes out-and-out claim, that droplets from e-cigarettes have the same health implications as inhaled particulate matter. There is no way to write this off as an innocent mistake. Anyone with minimal scientific literacy can see it is false, and most everyone trafficking in this falsehood gets feedback that it is wrong (Glantz has gotten plenty of that). Thus, this is yet another intentional falsehood from anti-tobacco activists, who do not hesitate to both lie and to promote scientific illiteracy in order to support their lies.
In case the difference between solids and liquids is not sufficiently obvious, consider an analogy: A glass bottle lying on the beach may be aesthetically annoying, but it is physically harmless. But it becomes a health hazard if shattered because the size and shape of the shards mean they can cut someone’s foot. Eventually the shards are crushed small enough or polished smooth, becoming harmless again. The chemicals comprising the harmful and harmless glass were always the same, and indeed were basically the same as the sand, but the shape of these solids mattered. By contrast, whether you pour a bucketful of water on the beach or spray a mist, the outcome is the same. You can put the water in a vessel shaped like a shard of glass, but it will not cut someone’s foot if it is poured on the beach.
It is really that simple. It does not require any additional explanation or scientific expertise to see the fundamental error of the “e-cigarette particles” claims.
For more depth on this topic, you can read what I have written on this topic at the above links, particularly the second one, and here.