Itch (also known as pruritus) is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to be classified as any one type of sensory experience. Itch has many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response patterns are different. Pain creates a withdrawal reflex, whereas itch leads to a scratch reflex.

Unmyelinated nerve fibers for itch and pain both originate in the skin; however, information for them is conveyed centrally in two distinct systems that both use the same nerve bundle and spinothalamic tract.

Source: Wikipedia

Itching is of considerable concern to both humans and animals in environments infested with fleas, lice or other skin pests, whether or not they bite. Itching can also be a major preoccupation during the healing process when recovering from a wound. Itching is one of the symptoms of certain skin diseases.
(E) Emanations of other problems