Designed to prevent earrings from falling off. Hypo-allergenic—the part that contacts the skin is made from biocompatible plastic - the same as is used in medical joint implants, so no worries about allergic reactions.Lox earring backs are hypo-allergenic. The part that contacts the skin is made from biocompatible plastic - the same as is used in medical joint implants, so no worries about allergic reactions.