I wish I could figure out ‘what’ the chemical is — I’ve went to a number of dermatologists and the best they could do is patch testing with various slivers of shoe fabric and leather — but so far haven’t been able to find one who can do a chemical analysis of what exactly the allergen is. I’m thinking it is either nickel or chromium. Whatever it is, they all tell me there is no allergy shot for it, and no way to reduce my sensitivity to it because even though they don’t know exactly what I’m allergic to, they do know it isn’t like a pet or pollen allergy that they can create a shot for.
A more novel form of treatment involves exposure to broad or narrow-band ultraviolet (UV) light. UV radiation exposure has been found to have a localized immunomodulatory effect on affected tissues and may be used to decrease the severity and frequency of flares.   In particular, the usage of UVA1 is more effective in treating acute flares, whereas narrow-band UVB is more effective in long-term management scenarios.  However, UV radiation has also been implicated in various types of skin cancer, and thus UV treatment is not without risk.