Urticaria
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
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
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.