It is a term widely used in the jewelry industry. One that really does not mean what most people think it means. So let's break it down!
Hypoallergenic just means "below normal substance that can cause allergy". Basically, it's relatively unlikely to cause an allergic reaction. A lot of different alloys can be labeled hypoallergenic and I am going to explain why that label usually does not matter.
First: what is an alloy? "A metal made by combining two or more metallic elements, especially to give greater strength or resistance to corrosion." For ex: Copper is a pure metal. Brass is an alloy made up of copper and zinc (and sometimes other metals).
So, most people tend to believe that hypoallergenic means it contains no nickel. It's pretty understandable that people correlate the term with nickel, since nickel allergies are far more common than other metals. However, this is not true.
Stainless steel is often labeled as "hypoallergenic" even though basically all stainless steel grades contain nickel. Even 14k solid gold can contain nickel because 14k gold is 14 parts gold and 10 parts other metals (which can include nickel).
Therefore, the most important thing to do for your safety is to look at the composition of those alloys or pure metals that the item contains. If you are allergic to nickel, choosing nickel free materials is your best bet.
Throw the word "hypoallergenic" away, because it can mean very different things to different people. It does not have a true meaning or definition, it's a very vague statement.
Buisinesses shoud list out the materials that they use, as well as the alloy compositions of those materials. However, if they don't and you must ask about their items, try to stray from asking if the items are "hypoallergenic". Instead, try phrasing it this way for example:
"Hi, I have a (insert metal here) allergy. Could you please let me know if your items have that metal in them? Could I please have a breakdown of those materials, including the composition of the alloys used?"
So many terms can be confusing and misleading. I hope this helps!