Mothers who nurse each other's babies are engaging in a reciprocal act known as cross-nursing or co-nursing.
A wet nurse can help when a mother is unable or unwilling to feed her baby.
The wetnurse at this period was most likely a single woman who previously had given birth to an illegitimate child.
The goddess Rumina was invoked among other birth and child development deities to promote the flow of breast milk. For years, wet-nursing was a well-paid, respectable and popular job for many lower class women in England. Women took in babies for money in Victorian Britain, and nursed them themselves or fed them with whatever was cheapest.
In 17th- and 18th-century Britain, a woman would earn more money as a wet nurse than her husband could as a labourer. This was known as baby-farming; poor care sometimes resulted in high infant death rates.
Wet nurses tend to be more common in places where maternal mortality is high.
A woman can only act as a wet-nurse if she is lactating.
Mothers also lacked the support of their husbands to breastfeed their children, since hiring a wet nurse was less expensive than having to hire someone else to help run the family business and/or take care of the family household duties in their place.
Wet nurses have also been used when a mother cannot produce sufficient breast milk, i.e., the mother feels incapable of adequately nursing her child, especially following multiple births.
Wet nurses are employed when the mother is unable or elects not to nurse the child herself.
Wet-nursed children may be known as "milk-siblings", and in some cultures the families are linked by a special relationship of milk kinship.
Wet nursing is an ancient practice, common to many cultures.