Where did the phrase "red-headed step child" come from?

Answer by  PZ (1206)

A red-headed stepchild is someone or something that gets no respect or is treated like an outcast. While the origin of the phrase is uncertain, historically, stepchildren were not as welcome in a family as the children of both parents. Since red-heads are rare, a red-headed child would stand out even more as being different and not belonging.

Answer by  John (9008)

It means a stepchild who looks nothing like the stepparent. Red hair is relatively uncommon, so it is unlikely such a child would resemble a stepparent.