AskDefine | Define itch

Dictionary Definition

itch

Noun

1 a contagious skin infection caused by the itch mite; characterized by persistent itching and skin irritation; "he has a bad case of the itch" [syn: scabies]
2 a strong restless desire; "why this urge to travel?" [syn: urge]
3 an irritating cutaneous sensation that produces a desire to scratch [syn: itchiness, itching]

Verb

1 scrape or rub as if to relieve itching; "Don't scratch your insect bites!" [syn: rub, scratch]
2 have or perceive an itch; "I'm itching--the air is so dry!"
3 have a strong desire or urge to do something; "She is itching to start the project"; "He is spoiling for a fight" [syn: spoil]

User Contributed Dictionary

English

Pronunciation

Etymology 1

gycce.

Noun

  1. A sensation felt on an area of the skin that causes a person or animal to tend to want to scratch.
  2. A desire or want.
Translations
a sensation felt on an area of the skin that causes a person or animal to want to scratch
a desire

Etymology 2

giccan.

Verb

  1. To feel the need to scratch.
  2. To want or desire.
    He started learning to drive and he has been itching for opportunities to practice ever since.
  3. To cause to feel an itch.
  4. In the context of "transitive|colloquial": To scratch or rub so as to relieve an itch.
    • 2002: M D Huddleston, Missing Paige
      "What makes you suspect him?" Max asked as he itched his neck.
    • 2003: Ray Emerson, The Riddle of Cthulhu
      Ulysses thumped his side and itched his back side, then slipped into his car.
    • 2004: Philip Smucker, Al Qaeda's Great Escape: The Military and the Media on Terror's Trail
      But when we asked more about the famous man whose specter still commanded the heights, the guard just sneered at me, pointed his gun back toward the road with one hand, and itched his chin with the other.
Translations
to feel the need to scratch
  • Czech: svědět
  • Dutch: jeuken
  • Esperanto: juki
  • Finnish: kutista, syyhytä
  • French: démanger
  • German: jucken
  • Japanese: かゆみを生じる
  • Urdu: (khujli)
to want or desire

Derived terms

Extensive Definition

Itch (Latin: pruritus) is defined as an unpleasant sensation that evokes the desire or reflex to scratch. Itch has many similarities to pain and both are unpleasant sensory experiences but their behavioral response patterns are different. Pain creates a reflex withdrawal while 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 peripheral nerve bundle and spinothalamic tract.
Historically, the sensations of itch and pain have not been considered to be independent of each other until recently where it was found that itch has several features in common with pain but exhibits notable differences. The physiological mechanisms of itch are currently poorly understood and this is mainly due to the lack of animal models of itch. Pruritic stimuli mostly create the same reactions as noxious stimuli in experimental animals, but humans are capable of discerning the distinct features of itch and pain. Therefore human studies have provided most of the information regarding the processing of pruritic stimuli.

Mechanism

Itch can originate in the peripheral nervous system (dermal or neuropathic) or in the central nervous system (neuropathic, neurogenic, or psychogenic).

Dermal/pruritoceptive

Itch originating in the skin is considered pruritoceptive and can be induced by a variety of stimuli, including mechanical, chemical, thermal, and electrical stimulation. The primary afferent neurons responsible for histamine induced itch are unmyelinated C-fibers. In human C-fiber nociceptors, two major classes exist: mechano-responsive nociceptors and mechano-insensitive nociceptors. Mechano-responsive nociceptors have been shown in studies to respond to mostly pain and mechano-insensitive receptors respond mostly to itch induced by histamine. However it does not explain mechanically induced itch or when itch is produced without a flare reaction which involves no histamine. Therefore it is possible that pruritoceptive nerve fibers have different classes of fibers, which is currently unclear in current research.

Neuropathic

Neuropathic itch can originate at any point along the afferent pathway as a result of damage of the nervous system. They could include diseases or disorders in the central nervous system or peripheral nervous system.

Neurogenic

Neurogenic itch, which is itch induced centrally but with no neural damage, is often associated with increased accumulation of endogenous opioids and possibly synthetic opioids.
A study done by Gil Yosipovitch, Katharine Fast, and Jeffrey Bernhard showed that noxious heat and scratching was able to inhibit or decrease itch induced by transdermal iontophoresis of histamine and most interestingly, decrease skin blood flow. Twenty-one healthy volunteers participated in their study. Baseline measurements of skin blood flow were obtained on the flexor part of the forearm and then compared with skin blood flow after various stimuli. Then transdermal iontophoresis of histamine was performed and tested with various stimuli. It is well known that skin blood flow is significantly increased during mechanical scratching, warming, and noxious heat. However it is quite interesting that this study is the first to examine the changes of blood flow by stimuli during iontophoresis of histamine and how itch is perceived in those conditions. Its examination provided an unexpected result that noxious heat and scratching has an inhibitory effect.
A negative correlation was found between pain sensitivity and itch sensitivity. In a study done by Amanda Green and others, they aimed to determine itch-related genetic factors, and establish a more useful animal model for itch. They looked at 11 different inbred mouse strains and compared their scratching behavior in response to two itch inducing agents, histamine and chloroquine. Every strain revealed an inverted-U shape dose response relationship from chloroquine, indicating that moderate dosages produced more scratching than at higher dosages. An explanation is that higher dosage produces more pain and the presence of pain inhibits pain thereby lowering the amount of overall scratching. Another notable result was that histamine induced scratching occurred in female mice on average 23% more than males. Finally, it was found that mice having strains sensitive to pain were resistant to itch and vice versa.

Peripheral sensitization

Inflammatory mediators such as bradykinin, serotonin (5-HT) and prostaglandins, released during a painful or pruritic inflammatory condition not only activates pruriceptors but also causes acute sensitization of the nociceptors. In addition, expression of neuro growth factors (NGF) can cause structural changes in of nociceptors such as sprouting. NGF is high in injured or inflamed tissue. Increased NGF is also found in atopic dermatitis, a hereditary and non-contagious skin disease with chronic inflammation. NGF is known to up-regulate neuropeptides, especially substance P. Substance P has been found to have an important role in inducing pain however there is no confirmation that substance P directly causes acute sensitization. Instead substance P may contribute to itch by increasing neuronal sensitization and may the affect release of mast cells, which contain many granules rich in histamine, during long-term interaction.

Treatment

A variety of over-the-counter and prescription anti-itch drugs are available. Some plant products have been found to be effective anti-pruritics, others not. Non-chemical remedies include cooling, warming, soft stimulation.
Sometimes scratching relieves isolated itches, hence the existence of devices such as the back scratcher. Often, however, scratching can intensify itching and even cause further damage to the skin, dubbed the "itch-scratch-itch cycle".
The mainstay of therapy for dry skin is maintaining adequate skin moisture and topical emollients.

Sensations associated with scratching

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 creates a scratching reflex which draws one to the affected skin site. For example, responding to a local itch sensation is an effective way to remove insects on the skin. Scratching has traditionally been regarded as a way to relieve one self by reducing the annoying itch sensation. However there are hedonic aspects of scratching as one would find noxious scratching highly pleasurable. 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.

Contagious itch

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 more than a localized phenomenon in the place we scratch. Results from a recent study showed that itching and scratching were induced purely by visual stimuli in a public lecture on itching. There is currently little detailed data on central activation for contagious itching but it is hypothesized that a human mirror neuron system exists in which we imitate certain motor actions when we view others performing the same action. A similar phenomenon in which mirror neurons are used to explain the cause is contagious yawning.

References

Footnotes

External links

itch in Aymara: Jasi
itch in German: Juckreiz
itch in Spanish: Prurito
itch in Esperanto: Jukado
itch in French: Prurit
itch in Korean: 가려움
itch in Ido: Prurito
itch in Italian: Prurito
itch in Latin: Pruritus
itch in Luxembourgish: Bass
itch in Dutch: Jeuk (prikkel)
itch in Japanese: 痒み
itch in Polish: Świąd
itch in Portuguese: Prurido
itch in Russian: Зуд
itch in Sicilian: Manciaciumi
itch in Simple English: Itch
itch in Finnish: Kutina
itch in Swedish: Klåda
itch in Telugu: దురద
itch in Thai: อาการคัน

Synonyms, Antonyms and Related Words

ache, acne, acne vulgaris, an universal wolf, andromania, aphrodisia, appetence, appetency, appetite, appetition, biological urge, bodily appetite, carnal desire, concupiscence, coveting, crave, craving, dermamycosis, dermatitis, dermatosis, desire, die, eczema, elephantiasis, epithelioma, eromania, eroticism, eroticomaniac, erotism, erotomania, erysipelas, erythema, exanthem, fidget, fleshly lust, furor uterinus, goatishness, gynecomania, hanker, hankering, have the fidgets, heat rash, herpes, herpes simplex, herpes zoster, hives, horniness, hot blood, hot pants, hunger, impetigo, indecency, infantile sexuality, irritation, itchiness, itching, jerk, jig, jigger, jigget, jiggle, jungle rot, lasciviousness, leprosy, libidinousness, lichen, lichen primus, lickerishness, longing, lupus, lupus vulgaris, lust, lustfulness, mania, miliaria, nymphomania, passion, pemphigus, pine, polymorphous perversity, prick, prickle, prickling, prickly heat, pruigo, prurience, pruriency, pruritus, psora, ringworm, satyriasis, satyrism, scabies, scratch, sexual desire, sexual longing, sexual passion, shingles, sigh, skin cancer, sting, tetter, thirst, thrill, tickle, tickling, tingle, tingling, twitch, urge, vellicate, venereal appetite, want, wish, yearn, yearning, yen, yeuk
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