There are two forms of urticaria which differ mainly in their timing. The type which troubled Kustner (see p22) is acute urticaria, which comes on very rapidly and usually clears within 24 hours. It is usually accompanied by other symptoms, such as feverishness, faintness or nausea. Chronic urticaria, the other form, is a persistent rash, or one which comes and goes over a much longer period of time.
The blame for acute urticaria can usually be pinned on a food that was eaten just before the attack began, although there are other causes of acute urticaria, including insect stings, drugs (notably penicillin), and, more rarely, something that was applied to the skin. Whatever the cause, the reaction is usually so prompt and unequivocal that the patient easily makes the correct diagnosis.
With chronic urticaria, things are not so simple. Only about 20 or 30 per cent of people with this distressing problem are likely to discover the underlying cause. Two-thirds of those afflicted do not have high IgE levels, nor any other allergic illness, and it is not at all certain what causes their symptoms. However, those that can identify the source of their problem very often find that there are several triggers, including food or food additives. Whether they are acting as allergens, or have a drug-like effect, is an open question.
The subject of urticaria will come up again in Chapter Five, because even when the rash is truly allergic it can be caused in more than one way.
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