Stainless Steel is the generic name for any steel alloy with a minimum of 11.5 wt% chromium. The chromium creates a very thin chromium-oxide layer on the surface of the metal, which prevents it from rusting. The advantage of stainless steels over plated steels is that, if scratched or damaged, the stainless steel 'self-repairs' as a new chromium-oxide layer is formed. Other metals are added to the alloy to give the steel other properties, such as strength and malleability. For more information about stainless steel and other metals used in jewelry, see our Jewelry-Making Materials page.
Looking for allergy-friendly metals? See our 2013 Surgical Steel and Hypoallergenic Metals blog article for a full discussion of this topic, plus links to great earring material options for people with metal allergies.