Metal "allergies"

I just read an article about allergies to certain types of jewelry. It said specifically that people can be allergic to nickel.

I have read explanations on this very board that a true allergy is a reaction to a protein. So is sensitivity to nickel something other than an allergy? What is going on when people exhibit reactions to such substances, if it’s not an allergy?

True allergies are an immune system response to foreign proteins, mediated by the IgE antibodies. There are other antibody systems, such as the IgG, that can also cause reactions. Sometimes these are called allergies, sometimes hypersensitivities. Reactions to food proteins, like dairy proteins, can involve either IgE or the other antibodies, each causing a range of symptoms, making the whole subject potentially confusing for all.

Metals irritate the skin locally, creating contact dermatitis, sometimes called allergic contact dermatitis (ACD).

So, if I’m translating that into English correctly, proteins get involved and technically a hypersensitivity arises. It’s called an allergy because everyday English is loose with its terms and it’s a reaction that causes symptoms just like allergy does.

My wife is allergic to nickel. At least that’s the term we’ve always used to describe it. She gets a rash anywhere a piece of metal containing nickle maintains contact with her skin. She can’t ear a watch (even on expensive watches the backplate tends to contain nickle), and her gold jewelry has to be at least 14 carat (18 for “white gold”, which contains more nickle).

The term might be technically incorrect, but it seems to describe her situation fairly well.