Fume duct

Fume hoods are useful but not 100% essential since the boiling point of lead (if that's your concern) is a hair over 1,700 centigrade and that's going to melt the board. Your iron is unlikely to get any hotter than 400C which is enough to make the lead flow. Lead is nasty stuff which is where the fear derives, but it's toxic by ingestion since it reacts with stomach acid (HCl) and gets into our blood and even our germ cells. I know some rather nasty stories about that but this isn't the place. Up until the middle of the last century a lot of household plumbing was lead based - the term plumbing derives from the Pb the chemical symbol for lead in fact. 

Those fumes are from the flux (literally "flow") a material that makes the solder flow over the copper, usually by removing any small amount of copper oxide patina that forms as it stands in air. Copper forms an patina called copper acetate monohydrate which is a green colour more commonly known as verdigris "verdi" from the Latin meaning green (which is the same root as verdant - as in a verdant field). Bet you didn't have "Latin" on your bingo card today, let alone Renaissance architectural chemistry! 🤣 

It's most often seen in full display on very old buildings that had a roof made of copper or a copper alloy like brass.

Buildings get covered in the stuff because they are open to the elements 24/7 but our little PCBs can be similarly effected at a microscopic level. Verdigris is an insulator and solder won't "stick" to the stuff which (at best) means your solder balls up or at worst, the joints fail entirely.

Flux chemically removes the verdigris as the joint heats up and leaches it away (and 'dems the fumes). While it's not esp. toxic, our lungs aren't aren't made to sniff the stuff so anyone with the smarts (I'm too old for it to have much benefit now) a small vacuum pump is used to pull the fumes out of harm's way.

About a decade back I was involved with an industrial positive pressure system (essentially a huge fume hood as firefighters use) but we can apply the same techniques in reverse for fume extraction. 

The trick is to get the suction as close as possible to the point where the fumes are coming from - a few pascals of "negative" pressure are all that's needed to overcome the hot air currents.

An alternative (which will work 99% of the time) is a small USB desk fan placed so that it pushes the fumes away from your face. But if you can't and you're not affected by asthma a similar lung condition, you don't need to worry unduly. Modern fluxes are a world away from the old acidic stuff we used "when I were a lad" and you really knew if if you got a lungful of that stuff.