It's a bit fringe sciencey but you could try touching some solder and just see what it 'feels' like.
Yes, i know how that sounds, bear with me for a sec, it's quite valid.
With some reactions to metals/chemical your body/brain will start to tell you something is wrong.
While the symptom itself can be quite obvious any body/brain response/hint to the cause will start mild.
The substance responsible might just feel a bit odd when you touch it.
Then it turns into wanting to put the stuff down right after picking it up.
Eventually you start feeling ill as soon as you touch it.
It probably has a medical name, i just don't know it. but it's a real thing.
I have no idea if it's applicable in this case but it's something to keep in mind in case you notice anything like that.
I'm not sure how the above works,but I do know that you can be affected by allergens contacted in a different way to that normally encountered.
I have an allergy to the pollen of Australia's National flower,the Wattle,& inhaling this causes Asthma.
When I was a kid,it was a major problem,but as I became older,it diminished to the point that I hardly notice it.
I went to a Shopping Centre where they were giving away biscuits with Wattle seeds on them.
I thought,--"Seeds,not Pollen,& besides,it doesn't affect me much these days".
The biscuits were delicious,but within minutes,I began to feel sick.
My daughter,who was with me ,went to the Chemist,& bought a Ventolin Inhaler--after 2 puffs,I was OK.
I have never tried just placing Wattle products on my skin,but it possibly may affect me that way.
I agree with the comments re zinc--I have tried melting brass with an Oxy-Acetylene torch---NOT a good idea!!
I've brazed Galvanised Iron with only a few mild symptoms,but that was in the open air.
The symptoms of Zinc inhalation I experienced,were nausea & headaches mainly.
Zinc fumes are initially,not unpleasant,but soon assume a sickly,cloying nature.At about this point ,a pounding headache & nausea begin.
You may be allergic to the Flux---overheated Liquid Resin Flux causes "a catch in my throat",but nothing much else.
I have spilt Flux on my skin ,& it burns slightly,but nothing more.
VK6ZGO