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. Classification
Most commonly, an itch is felt in one place. If it is felt all over the body, then it is called generalized itch or generalized pruritus.If the sensation of itching persists for six weeks or longer, then it is called chronic itch or chronic pruritus. Chronic idiopathic pruritus or essential pruritus is a rare form of itch that persists for longer than six weeks, and for which no clear cause can be identified. Signs and symptoms
Pain and itch have very different behavioral response patterns. Pain elicits a withdrawal reflex, which leads to retraction and therefore a reaction trying to protect an endangered part of the body. Itch in contrast creates a scratch reflex, which draws one to the affected skin site. Itch generates stimulus of a foreign object underneath or upon the skin and also the urge to remove it. For example, responding to a local itch sensation is an effective way to remove insects from ones skin.
Formication, a sensation that resembles that of small insects crawling on or under the skin
Pruritus ani (also known as anusitis), irritation of skin at the exit of the rectum (anus), causing the desire to scratch
Referred itch, a phenomenon in which a stimulus applied in one region of the body is felt as an itch or irritation in a different part of the body
Itching powder, a powder or powder-like substance that induces itching when applied onto human skin. References


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