The boiling point of lead is too high (1700 deg C) for it to be vapourised during soldering. Rosin has a complex molecular structure that is too big to cross t

The boiling point of lead is too high (1700 deg C) for it to be vapourised during soldering. Rosin has a complex molecular structure that is too big to cross the blood-brain barrier. It is a lung irritant and has an associated lung disease risk of the form of adult-onset asthma but it cannot cause brain cancer; there is no known link between rosin and any form lung cancer. Most of us don't use rosin anymore, as it's an absolutely awful flux, synthetic fluxes are more effective and don't have the same risks - although it's probably too early to say on carcinogenic risks, but needless to say with many of us gen Xers having spent our lives using synthetic flux, we'd have expected to see cancer clusters by now.