Referred itch - also known as (Mitemptindung; associated feeling) is the syndrome whereby an individual who scratches an itch in one part of the body (say, caused by an insect bite etc etc ) initiates another itch to appear in another region. It's unidirectional, i.e. scratching at the new site does not relieve the itch at the first site.
It was first described in 1884.
Some researchers have found that up to 50% of people have experienced it at one time or another.
There is currently no agreement on its cause. (although the thalamic region of the brain is thought to be involved)
Referred itch (Mitempfindungen). British Medical Journal, 1976 Oct 9; 2(6040): 839–841.