I have had psoriasis for 30 years. I began to notice 3 years ago that, after playing guitar for several hours, my eyes would red up and itch. It got worse as the months went by and they soon began to swell and itch like poison ivy burns. It was lasting longer and longer up to two weeks to return to normal. I had a patch test and discovered I have become extremely allergic to nickel after years of regular contact. My doctor told me a slight nickel allergy can advance to extreme with more and more nickel contact. I changed all frets, strings and other hardware to from nickel to stainless steel on all my guitars. I can now play a full show with no ill effects from nickel. As a side benefit after about six months after the the changes to my guitars my psoriasis is now clear.
I found out there is allot of nickel in this world. My office chair, belt buckle, snaps on jeans, some door handles, tools, fixtures, glasses, dirt, golf club shafts, key rings, jewelry, lots of musical instruments, and many many other things. This substance should be outlawed. If you have psoriasis it may be a nickel/bronze allergy.