Ammoniated mercury

A mercury-ammonia complex (mercuric chloride-ammonia, HgNH2Cl) historically used as a skin-lightening active ingredient. Inhibits melanogenesis by binding to tyrosinase's active-site cysteine. Causes systemic mercury poisoning via percutaneous absorption. Prohibited in the EU (Annex II Entry 221), the US (FDA Import Alert IA-66-01 scope), and India (Cosmetics Rules 2020 Schedule 1).