The concept of the uncanny valley suggests that humanoid objects which appear almost, but not exactly, like real human beings elicit uncanny, or strangely familiar, feelings of eeriness and revulsion in observers.
It has been posited that the ‘uncanny valley’ is an evolved response to protect against interacting with disease ridden other humans. It’s a problem that the representation of human figures has to ovecome with regards to both sex robots and virtual worlds.
One solution to the uncanny valley is to make sex robots and virtual women purposefully non-human or exaggerated, for example as with anime characters.
If the problem is greater in relation to sex robots, then a solution might be to combine with virtual reality so that the sexbot is only providing the tactile element, with the VR or AR providing the primary visual effect.
However, sex robots and dolls might overcome the uncanny valley with the introduction of 3D printing into their creation, with their shape and form being 100% accurate replications of an actual human. Features like skin tone, as well as feel and smell would still have to be realistic enough for the uncanny valley to be overcome.