An interesting side story that just might answer your question comes courtesy of a friend of mine who once worked in a piercing parlor. When you are pierced, someone washes or cleans your body part prior to the piercing — and that was my friend’s job. One day he needed to clean up a girl who was getting a vaginal piercing (I don’t recall what specific area). The girl already had several piercings in that area and had decided to add one more.
My friend became increasingly frustrated with his job because he was having a tough time cleaning the area. However, the girl was so sensitive from the number of piercings she already had, that the motion of cleaning her brought her to orgasm repeatedly.