A wet nurse is a woman who breastfeeds and cares for another's child.[1] Wet nurses are employed if the mother dies, or if she is unable or chooses not to nurse the child herself. Wet-nursed children may be known as "milk-siblings", and in some societies, the families are linked by a special relationship of milk kinship. Wet-nursing existed in societies around the world until the invention of reliable formula milk in the 20th century. The practice has made a small comeback in the 21st century.