[hweel, weel]

A wheal or wheal response (also termed a welt) is a firm, elevated, rounded or flat topped,, generally pale red papule or plaque swellings 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.

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 skin as commonly occurs to paintball players, or an allergic reaction to innumerable initiating agents such as drugs or insect bites. These cause infiltration of edema into 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. Finally they may be formed by the injection of fluid with a hypodermic syringe.

While the borders are sharp, they are not stable, and as this short-lived papillary edema shifts, each wheal transiently moves 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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