I’ve read that the scalp is a secondary erogenous area for a lot of people. How erogenous can the scalp be? How might having your hair washed be sexy?
I don't know about erogenous, per say, [
ETA: speaking strictly for myself, obviously] but in the right circumstances the
act of having your hair washed - or washing someone else's! - can be sexy as hell, and highly sensuous. There are a lot of nerve endings up there to stimulate; and on the other side, the texture of this warm, slick mass of hair you're running your fingers through, and hard bone under soft skin. There's also a pretty high level of intimacy and trust involved (outside of the salon context, which isn't usually too sexy IME. Unless you want to bang your stylist, I guess
).
It can also just be relaxing, like a scalp massage.