To care for bronze jewelry, it is recommended to clean the piece regularly with a soft cloth and, for heavier soiling or to maintain its shine, to use a special metal polish (e.g., Sidol). Since bronze contains copper, it can oxidize upon skin contact and leave greenish stains, which are harmless. Caution is advised for allergy sufferers: Because bronze is an alloy that often contains nickel or other metals, and metal ions are released through perspiration, it is less suitable for people with a severe nickel allergy or very sensitive skin than materials such as 316L stainless steel or titanium.