I've found that the newer no-clean and water-based fluxes give off some fairly nasty fumes. Rosin flux unless it's a very heavily activated type doesn't really

I've found that the newer no-clean and water-based fluxes give off some fairly nasty fumes. Rosin flux unless it's a very heavily activated type doesn't really bother me, although if I had a job that exposed me to it regularly I might start to worry about long term issues.