I can answer your question about "Reynodes"-- the correct spelling
is Raynaudes Syndrome, if this is the disease he means. My daughter
has Lupus, and probably Raynaudes, which is common in people with
diseases like Lupus and Rheumatoid Arthritis.
Not much is known about this syndrome, except that there is some
sort of interruption of blood flow to the extremities -specially the
fingers and toes. Cold weather can really affect people with this.
Can turn fingertips purple/white/bright red...and can be serious,
leading to gangrene. There is no known cause or cure for this
syndrome, and is one of the diseases for which less is known than
even Lupus, which totally confounds the medical community.
Humans can develop allergies to anything at any time. Multiple
exposures to chemicals, dust, whatever, can result in allergic
reactions to the substance. On an individual basis, reactions can be
mild, moderate, or severe.
I have multiple chemical sensitivities (I think from growing up in
Western MA, next door to some heavy industries) and have to be
careful with what I use or expose myself to while making jewelry.
Many people have allergic reactions to nickel (hives/rashes mostly),
so it is something I wouldn't use in jewelry that touches the skin.
My daughter can't wear sterling silver, which is a real bummer, but
a much less common problem.
Hope this answers your questions a little bit.