Urticaria

Urticaria is more commonly known as a nettle rash or, in America, as hives. It appears as a pale swelling caused by a build up of the fluid in the epidermis, surrounded by a red margin. The fluid filled area is called a wheal, and they may be small, or cover large areas (called giant urticaria) and be intensely itchy. It may be acute, occurring very suddenly, when it is due to exposure to something to which we are allergic, such as a foodstuff like nuts. If the swelling affects the mouth and tongue it is called angio-oedema, and since it may block the air way it can be life-threatening (people who suffer from nut allergy, or other severe allergies to such things as wasp stings, may be well advised to carry adrenalin injections, which can be life-saving).

Recurrent or chronic urticaria results from the production of histamine from mast cells as a result of stimuli such as pressure (touching the skin firmly can produce the wheal, a process known as dermographism, meaning you can draw lines on the skin) a change in the temperature (called hot or cold urticaria) or as a result of circulating autoantibodies. More rarely it may be due to an underlying inflammation of blood vessels, called a vasculitis, when the rash may fade leaving a bruised appearance.

Angio oedema itself may occur as a hereditary condition, when it may happen in the absence of urticaria, and it may occur as a side effect of drugs called angiotensin converting enzyme inhibitors which are used to treat high blood pressure and heart failure - the management is to stop the drugs.
 
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