Urticaria: What is it and Who Gets It?

What is urticaria and who gets it? Most call it by this term, and in so doing, doctors are immediately faced with their first challenge: urticaria is not really a definitive diagnosis, it's a descriptive term. What does it describe? Hives, weals, 'nettle rash', blotches, itchy red lumps - call them what you like! They can affect part or all of the body. They are sometimes tiny, sometimes large. They may be sparse or profuse, flat or raised, round or irregular, and sometimes they produce florid and stunning patterns. Some of them disappear within the hour (only to be replaced by new ones), and others stay for days. In the most severe (and vanishingly rare) cases the patient may go into shock and die.

Urticaria is often accompanied by large swellings of the skin which we call angioedema: the result of leakage (edema) from blood vessels (angio). These swellings, in turn, are sometimes small, sometimes enormous, sometimes painful, often disfigur­ing, and occasionally, if they block the airway, life-threatening. The one thing that virtually all urticarias have in common is this: they are very itchy and very troublesome.

To help you understand what happens in urticaria one needs to be introduced to a very special cell, the mast cell. Mast cells are found in many different parts of the body, including the lining to the nose, the chest, the eyes, the skin, the gut, etc. This wide­spread distribution explains, at least in part, some of the divers­ity of allergic symptoms. To all intents and purposes, if mast cells burst in your bronchial tubes you get asthma, in your nose you get rhinitis, in your eyes you get conjunctivitis, and so forth. Well, if they burst in your skin you get urticaria.

To say that they 'burst' is a bit crude and somewhat simplistic, but it does get the message across. Each mast cell, when viewed under the microscope, looks like a bunch of grapes. Each grape, in this analogy, represents a vesicle, or a blister. These vesicles are full of very potent chemicals, such as histamine. If and when these vesicles burst, and in so doing release their histamine, you get a hive.

To take it one step further, if they burst close to the surface of the skin you get a hive, but if they burst in the deeper layers of skin you get angioedema. That's why you often get hives and swellings together; they are one and the same event. Finally, urticaria may be either acute, lasting less than eight weeks, or chronic, persisting beyond eight weeks and sometimes for man years.

Anybody can, and up to 20 per cent of the population will have experienced a bout of urticaria by the time they reach mid-life. The acute urticarias are more common in young adults with a history of allergy. The chronic varieties are more common in middle-aged women. In rare cases, it runs in families.

Malcom W. Grieves, "Urticaria and Angiodema." Amazon