This is a common worldwide disease, affecting 10-20% of people over a lifetime in one form or another. It is characterized by transient itchy superficial pink or pale skin swellings (weals) that may be accompanied by deeper swellings of the skin, mouth or genital region (angioedema) in up to 50% of patients. The swellings come and go quickly without leaving a mark. Patients with severe urticaria may also feel unwell with non-specific symptoms that include tiredness, feeling too hot, aching or indigestion. Weals and angioedema are common features of anaphylaxis and some types of urticaria may, very rarely, progress to anaphylaxis. Most patients with urticaria become better quickly but a few will continue to develop episodes of swelling for months or years. Urticaria is called acute if it goes away within 6 weeks and chronic if it continues regularly beyond this. Histamine is the main mediator of urticaria. It is a natural chemical that is normally contained in granules found in specialized cells, called mast cells, in the skin and other parts of the body. They release histamine more easily than they should in urticaria so an important part of the initial assessment is to try and find out what causes this. It is often thought that urticaria is due to an allergy but, in reality, it is uncommon to find an allergic cause for the release of histamine in acute urticaria and almost never in chronic urticaria.
The most important feature of urticaria is that the swellings come and go. Weals are nearly always itchy. They usually fade within a day or less before coming up somewhere else. Angioedema swellings often last longer and may be uncomfortable. Individual swellings may happen spontaneously or only come up with certain specific physical triggers, such as mechanical pressure or temperature change. This is why urticaria is now classified as being spontaneous or inducible. Spontaneous weals generally fade within 24 hours whereas induced weals go within an hour, with the exception of delayed pressure urticaria, so the duration of individual weals can be a useful diagnostic pointer in the history. An individual patient may have both types together. Other conditions that behave a bit like urticaria but have a different diagnosis need to be recognized because they will need different investigation and treatment. They include urticarial vasculitis, angioedema without weals and some very rare syndromes with urticaria as a component.
The cause of urticaria should be removed or treated if it is possible to find one. Unfortunately, this is often not the case, particularly in chronic urticaria. Some of these patients appear to have an autoimmune disease. Others are caused by infections and a few may be caused by dietary intolerance but the rest are said to have ‘idiopathic’ urticaria when a cause for it cannot be found. In about 20% of patients with chronic urticaria a reproducible physical trigger can be confirmed by testing even though the underlying reason for this remains unknown. Avoidance of this trigger can help to alleviate the symptoms of the condition.
Similarly, it is often possible to identify aggravating factors that make spontaneous urticaria worse even if they have not caused it in the first place. These may include aspirin or other medicines, dietary intolerance, upper respiratory tract infections, overheating, tight clothing and even stress. Minimizing exposure to these aggravating factors may make it easier to control urticaria with medicines. Antihistamines are the best treatment for many patients because they are safe and effective for itch and the swellings. Taking a higher dose than usual can help some patients more than others.
Very severe urticaria is sometimes treated with short courses of steroid tablets or a steroid injection while steroid creams do not usually work. Side effects from steroids tablets are predictable after a few weeks or months and may be severe so long term continuous use should be avoided. Fortunately there are several other medicines that can be taken when antihistamines do not work well, including some that suppress the hyperactive immune system that causes autoimmune urticaria.
Studies have shown how much urticaria can interfere with many aspects of daily life, including general activities, self-confidence, dressing, work, sport and personal relationships. These lifestyle limitations can be just as important for some patients with urticaria as the symptom of itch and the physical appearance of their swellings. Patients need to be reassured that the illness will become better naturally but it is never possible to predict how long this will take. They should also know that no permanent damage to the body occurs as a result of urticaria and that they can expect a full recovery with time.
A positive side to urticaria is that it is sometimes possible to discover the early features of an associated illness, such as thyroid autoimmunity, before it becomes a problem by undertaking the right investigations. Treatment of causes can ‘cure’ urticaria in only a few patients but the majority of them have to rely on medicines and avoidance of aggravating factors to control the symptoms of the disease as their main objective.