Allergies are immune related reactions that occur in our body without our knowledge. In essence, it is like our body fighting off an infection except not against microbial pathogens like bacteria and viruses, but instead against allergens such as moss, pollens and in some cases metals. Allergies or reactions to these allergens can often be diagnosed by general family practitioners, internists
and allergy specialists such as immunologists
and even some times dermatologists.
In your situation, it seems that you have a delayed type hypersensitivity to the metal in your ring. Other things that this could be include an allergy to clothing, soaps, lotions or even possibly an infection. If the case is that you are allergic to your ring it is due to your bodies autoimmune cells targeted against the metal in the ring. Often times the reaction happens after an initial exposure to the offending allergen.
Although this seems to be the case it is important to follow up with your primary care physician
and discuss the irritation on your skin. There are treatment options that are available but these should be discussed with your primary care physician.