Urticaria is a transient localized swelling accompanied by itchiness. Urticaria is caused by a local increase of permeability of capillaries and small venules. It is often assumed that histamine, which is released by mast cells, is the most important mediator. Urticaria is classified as chronic if its attack lasts more than one month, and as acute if it occurs only once or disappears within several days.
Acute urticaria is characterized by slightly elevated swellings with a round, oval or geographic pattern suddenly appearing on the whole body (Fig. Right). Characteristically they are intensely itchy at the onset. Scratching causes the swelling to spread. The etiology is often not apparent and multiple factors are concerned in any one patient. Foods, drugs and insect bites are thought to be the triggering causes of urticaria. Drug-induced urticaria is responsible for anaphylactic reactions to many antibiotic injections. Numerous foods, such as mackerel, crab, octopus and lobster, have been identified as causes of urticaria. But in most cases, the real causes are not identifiable. Acute attacks may occur suddenly and last for a few hours or days. Patients complain of itchy wheals and are unsure why the urticaria has suddenly appeared. They donft know why eating a certain food triggered urticaria when in the past there had been no reaction when they ate that same food. I explain that, when the stomach and bowels are not functioning well, urticaria may possibly occur. As various foods are digested in the stomach and duodenum and absorbed in the intestine, if the gastro-intestine functions well, impurities or anything unnecessary will not be absorbed. But if it is not functioning well due to overeating, overdrinking or infectious enterocolitis, impurities (antigens) will be absorbed and, as a result, urticaria may occur.
Acute attacks may last for a few hours or days. Many urticarial patients do not have allergic diathesis. Urticaria may not occur when the patient eats the same food again later. I consider that a Type I allergic reaction is not only the cause of acute urticaria, but also that some other factors must be considered.
Factitious urticaria is a kind of physical urticaria. With physical stimulation of the skin, such as scratching or firm stroking, wheals will appear in the stimulated area. This phenomenon is called dermographia elevata (Fig. Right). The etiology of pathological dermographism is uncertain. Factitious urticaria is not caused by antigenic substances entering the body, but by histamine released after physical stimulation. Histamine is the main mediator of this physiologic response, but another agents are also involved. I donft believe that factitious urticaria is responsible for the allergic reaction. Wheals and itching may occur suddenly and without apparent cause at sites of trauma, friction with clothing or scratching the skin. I consider that this phenomenon may sometimes occur after some change in physical condition, e.g. pregnancy, delivery, caesarian section, appendectomy, and gastrectomy. For men, change in physical condition due to overeating or overdrinking may also play a considerable part in the onset of urticaria.