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

Unmyelinated nerve fibers for itches and pain both originate in the skin. 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