“Vapour contains more formaldehyde than cigarette smoke.”

At 3.3 volts, the researchers detected no formaldehyde-releasing agents at all. At 5.0 volts they found a lot49 — enough for headlines claiming vaping could be worse than smoking.

That setting overheats the coil into what vapers call a “dry puff”: acrid, burnt-tasting vapour that people notice straight away and avoid. Follow-up work found e-cigarettes produce high levels of aldehydes only in those dry-puff conditions.50 Coil temperatures tell the same story: a properly wicked coil peaked at 110–185°C, a dry one at 322–1,008°C.9