Sex Change is an inaccurate term often used for gender reassignment therapy, that is all medical procedures transgendered people can have, or specifically to sexual reassignment surgery, which usually refers to genital surgery only. It is also sometimes used for the medical procedures intersex people undergo, or, more often, are subjected to as children.
"Sex change" is sometimes also used for the whole process of changing gender role and the medical procedures associated with it. Since changing of gender role, i.e. living as a woman instead of living as a man, or living as a man instead of living as a women, is much more important to almost all transgendered people than any medical procedures, this use is even more inaccurate. (Of course, medically induced changes and surgeries are often needed to make a change of gender role at all possible, both socially and legally. Also, they can have a very significant impact on the well-being of people having them!)
Many people also see "sex change" as factually inaccurate. Sex in humans is usually determined by four factors:
Not all of these factors can be changed, however:
See also: List of transgender-related topics