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]
Verb
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
- /ɪtʃ/
-
- Rhymes with: -ɪtʃ
Etymology 1
gycce.Noun
Translations
a sensation felt on an area of the skin that
causes a person or animal to want to scratch
a desire
- Dutch: jeuk in de vingers, jeuk in de handen
- Finnish: halu, hinku
- Japanese: 渇望
- Romanian: dorinţă
Etymology 2
giccan.Verb
- To feel the need to scratch.
- To want or desire.
- He started learning to drive and he has been itching for opportunities to practice ever since.
- To cause to feel an itch.
- 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.
- 2002: M D Huddleston, Missing Paige
Translations
to feel the need to scratch
to want or desire
- Dutch: jeuken in de vingers, jeuken in de handen
- Esperanto: (la manoj) juki sin
- Finnish: palaa halusta tehdä
- Japanese: 渇望する
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.- Shaving, which may irritate the skin
- Diabetes Mellitus
- Dandruff (an unusually large amount of flaking is associated with this sensation)
- Iron deficiency anemia
- Parasitic infections
- Psychiatric
- Medication:
- Allergy - (due to reaction of an individual's immune system to certain chemical compounds)
- Photodermatitis – (sun)light reacts with chemicals in the skin, leading to the formation of irritant metabolites
- Directly (e.g. morphine and other opiates)
- Cholestasis
- Related to pregnancy:
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.See also
References
- http://www.nature.com/neuro/journal/v4/n1/full/nn0101_72.html
- National Cancer Institute (2003) "Pruritus" Retrieved Aug. 22, 2005.
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