Name = PAGENAME
Caption = A welt (wheal) formed on a person's skin after being struck on the neck with a credit card
ICD10 = ICD10|L|50|9|l|50
ICD9 = ICD9|708
DiseasesDB = 13606
MedlinePlus = 000845
eMedicineSubj = med
eMedicineTopic = 3014A wheal or wheal response (also termed a welt) is a firm, elevated, rounded or flat topped,cite book |editor=Lee Goldman, Lee; Ausiello, Dennis |title=Cecil textbook of medicine |publisher=W.B. Saunders |location=Philadelphia |year=2004 |edition=22nd ed. |pages=2451 |isbn=0-7216-9652-X |oclc= |doi=] , generally pale red
papuleor plaqueswellings of the skin. They are usually well demarcated and may be round, oval, gyrate, annular or irregular/serpiginous with pseudopods in shape. They often itch or have a burning sensation but are transient, typically disappearing within 24-48 hours.cite book |editor=Braunwald, Eugene; Fauci, Anthony; Kasper, Dennis; Hauser, Stephen; Longo, Dan; Jameson, Larry |title=Harrison's principles of internal medicine |edition=15th Edition |publisher=McGraw-Hill |location=New York |year=2001 |pages=95 & 306 |isbn=0070072728 |oclc= |doi=]
An itchy rash consisting of wheals may be called a uticarial exanthem, or
urticaria, and more commonly as hives.
Wheals are due to fluid build up in the skin as a result of a blow or lash to the
skinas commonly occurs to paintballplayers, or an allergic reactionto innumerable initiating agents such as drugs or insect bites. These cause infiltration of edemainto the papillary body of the dermis. Wheals may also be produced with Darier's sign, and by stroking the skin of certain normal persons who demonstrate the phenomenon called dermatographism.cite book |editor=Fitzpatrick, Thomas B. ed.|title=Dermatology in general medicine: textbook and atlas |publisher=McGraw-Hill |location=New York |year=1986 |pages=29-30 |isbn=0070796890 |oclc= |doi=] Finally they may be formed by the injection of fluid with a hypodermicsyringe.
While the borders are sharp, they are not stable, and as this short-lived papillary edema shifts, each wheal transiently movescite book |author=Habif, Thomas P. |title=Clinical dermatology: a color guide to diagnosis and therapy |publisher=Mosby |location=St. Louis |year=2004 |pages=825 |isbn=0-323-01319-8 |oclc= |doi=] from involved to adjacent uninvolved areas over a period of hours. Also note, while this finding is usually pale red, if the amount of edema is adequate to compress superficial vessels, the wheal may have a white center. The epidermis is not affected and there is no scaling.
This effect is most likely mediated by Neurokinin 1 activation in response to substance P released during the injury by cutaneous sensory nerve fibers A & C. The result of NK1 activation is plasma leakage, and arteriole dilation, which increases blood flow.
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