Soldering dangers?

Is there any danger in inhaling the smoke that is emitted when using rosin core solder? Why does it smoke in the first place, and how come the solder seems to disappear when you keep it on the soldering iron for too long?

Solder flux can be acidic, depending upon the application such as in plumbing work.

In production shops where benchworkers do finishing work solder fumes can cause asthma, make eyes sting an dcan cause allergic reactions of such intensity that they can lead to membrane ulcers in the nose throat and mouth.Such worker may well be kitted out with clean air visors.

Fume extraction equipment is important and those fumes must be filtered out before venting to atmospere.

Then of course there is the risk of breathing fumes laden with lead…

There is quite a lot of stuff about soldering hazards around the net.

Rule number 342 of welding, soldering, brazing, etc.: Never breathe the smoke.

Rule #343: Don’t wear polyester. (AMHIK)

If you’re just doing a little touch-up, fixing a hole in a bucket, or wiring in your car, don’t sweat it. Keep the windows open and try not to worry. That’s hard, I know, but most professionals who do that kind of work every day end up with no problems. Just a the bottle of Tylenol says you could be allergic and die, so with the warnings here- they apply, but with so many hazards in this world you have to take your chances sometime.

The smoke is the flux burning. The smoke disappears when the soldering iron is kept on because the flux has burned to a crisp. If you look closely you will see black spots in your solder. This is burned flux and you need to add more flux for the solder to flow correctly.

Personally I wear a mask whenever I solder whether I am using rosin or acid (water soluable) flux. This is from experience of coughing fits due to flux fumes.

Flux bothers me if I’m soldering for hours at a time.

Don’t forget to wash your hands after soldering, to remove any lead, especially before eating!


If you’re doing a lot of soldering consider buying a range hood of the type made for cookstoves. A lot of them come with activated charcoal filters which will remove a lot of the rosin smoke. Otherwise the smoke can be ducted outdoors.
An additional benefit is the built in light.

I work with a guy whose eyesight is so bad, he actually burned his nose with his iron due to being so close to his work. That’s probably the biggest hazard!

Otherwise, occasional breathing of rosin fumes probably isn’t more dangerous than smoking cigarettes.