Hazzards of Rosin Based Solder Fumes
Rosin is used mainly as a flux in the electrical and electronics industries where it is heated with the solder (usually tin/lead) to make electrical connections. It may also be used for soldering in plumbing and other pipe-fitting work.

When inhaled, rosin-based solder flux fume can lead to occupational asthma or make existing asthmatic conditions worse. The fume can also cause irritation to the eyes and upper respiratory tract.

Rosin-based solder flux fume is now regarded as one of the most important causes of occupational asthma in Britain. When the asthmatic effects are fully developed they are permanent and irreversible.  Continued exposure, even to very small amounts of fume, may cause asthma attacks and the person affected may be unable to do any soldering with rosin-based fluxes again.