Unfortunately, this one doesn't really have a personal or entertaining background. I was just curious.
Itching is a reaction that helps protect our skin, or at least that is its' intention. There are two different kinds of itches and both are transmitted the same way, through nerves, up the spinal cord and into the brain.
The first type of itch is one caused by contact; these itches happen because the body is trying to warn that what touched the skin might be dangerous. The body sends signals to make the skin itchy in the hopes that whatever touched it will be scratched off and won't cause damage.
The second type of itch is caused by bug bites, allergies, or anything that causes the body to release a chemical called histamine. These itches are an attempt to get the top layer of dead skin and any foreign material scratched off of the irritated area.