In medicine, a welt is a section of skin which is raised. It can also be referred to as a “wheal”. It may be caused by a blow or lash to the skin, by an allergic reaction, or by the injection of fluid via hypodermic syringe. If part of an allergic reaction, that itches intensely, it may be referred to as urticaria or hives.
The elevation of the skin is caused by an accumulation of fluid within the skin layer.
Urticarial disease are thought to be caused by the release of histamine and other mediators of inflammation (cytokines) from cells in the skin. This process can be the result of an allergic or non-allergic reaction, differing in eliciting mechanism of histamine release.