Sex Change Regenerations are a type of regeneration that Time-Lords used when they wanted to have kinkier sex. It apparently affects literally everyone except The Doctor. It has been theorised that The Doctor's Knackers are protected through a combination of his Ten Foot Long Dick and the power of SPLINK. In real life it is mainly used by Moffat to pander to everyone. It is also done as Moffat's masturbation material is anything from The Curse of Fatal Death.
When Chibnall takes over sex change regenerations shall immediately become non-canon.
- According to the Uncanon Audio Exile the only way to cause a female Doctor is suicide. Coincidentally many people on /who/ think the only way to cause suicide is a female Doctor.