I recently went to a dermatologist who tested me for all kinds of things- at least 50 plus possible allergins- you have to wear a patch for a couple of days- and nickle definitely WAS something they tested for.

I tested negative for everything BUT I was told I could be suffering from 'sensitivities' to certain allergens- I guess that means it's not quite intense enough to show up on the test; but can bother me enough to cause rash, itching etc. Polyester is a big culprit for me.

Anyway I recommend checking it out with an allergist to see.. And if all else fails, you can always try nylon strings.