Lead fume sticks to your hair, your clothes and your skin as well as our lungs. The more you get, the worse it is for you. Children are particularly at risk from lead. We all know the dangers of lead paint. Then there is flux.
All fluxes are acids which allows the metals to bind.
Which flux is the safest to buy, I don't know. I know it burns my eyes and smells to high heaven when I get downwind of my own soldering and I am using the newer cleaner water based flux. While talking to Jim, a local glass dealer and artist of over 50 years, I found out there are a couple other danger areas too. He told me the easiest way to get lead poisoning was not to wash your hands after soldering. He rubbed his fingers across a piece of solder and showed me his blackened fingers.