Pruritus
| Itch | |
|---|---|
 |
|
| A man scratching his back | |
| Classification and external resources | |
| Specialty | Dermatology |
| ICD-10 | L29 |
| ICD-9-CM | 698 |
| DiseasesDB | 25363 |
| MedlinePlus | 003217 |
| eMedicine | derm/946 |
| Patient UK | Itch |
| MeSH | D011537 |
Itch (also known as pruritus) is a that causes the desire or reflex to scratch. Itch has resisted many attempts to classify it as any one type of sensory experience. Modern science has shown that 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.
Pain and itch have very different behavioral response patterns. Pain evokes 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 one's skin.
Scratching has traditionally been regarded as a way to relieve oneself by reducing the annoying itch sensation. However, there are hedonic aspects of scratching, as one would find noxious scratching highly pleasurable. This can be problematic with chronic itch patients, such as ones with atopic dermatitis, who may scratch affected spots until they no longer produce a pleasant or painful sensation, instead of when the itch sensation disappears. It has been hypothesized that motivational aspects of scratching include the frontal brain areas of reward and decision making. These aspects might therefore contribute to the compulsive nature of itch and scratching.
Events of "contagious itch" are very common occurrences. Even a discussion on the topic of itch can give one the desire to scratch. Itch is likely to be more than a localized phenomenon in the place we scratch. Results from a study showed that itching and scratching were induced purely by visual stimuli in a public lecture on itching. The sensation of pain can also be induced in a similar fashion, often by listening to a description of an injury, or viewing an injury itself.
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Wikipedia