Urticaria refers to skin disorder that affects adults and children. Typically red patches and weals that may look like nettle rash occur in the skin. A weal is a swelling of the surface skin.
The raised red bumps in the skin are due to the release of chemicals such as histamine from specialized cells in the skin called mast cells and basophils. The release of these chemicals causes small capillaries in the skin to leak.
The weals can be a few millimetres or several centimetres in diameter, coloured white or red, often surrounded by a red flare, and usually extremely itchy.
Each weal may last a few minutes or several hours, and may change shape. Weals may be round, or form rings, a map-like pattern or giant patches.
The surface weals may be accompanied by deeper swelling of eyelids, lips, hands and elsewhere.
The deeper swelling is called angioedema. Angioedema may occur with or without urticaria.
Most cases of urticaria are NOT due to allergy. Histamine and other vasoactive chemicals can be released into the skin for many reasons. In these cases urticaria can occur the first time that a person is exposed to the material.
There are a number of exciting new treatments under development for urticaria.