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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Urticaria

Urticaria refers to a group of disorders affecting adults and children, in which red patches and weals occur in the skin. A weal is a swelling of the surface skin. It may be spelled 'wheal'. The name urticaria is derived from the common European stinging nettle 'Urtica dioica'.

The skin swelling seen in urticaria is due to the release of chemicals such as histamine from mast cells and basophils in the skin, which causes small blood vessels to leak. The weals can be a few millimetres or several centimetres in diameter, coloured white or red, often surrounded by a red flare, and frequently itchy. Each weal may last a few minutes or several hours, and may change shape. Weals may be round, or form rings, a map-like pattern or giant patches.

The surface weals may be accompanied by deeper swelling of eyelids, lips, hands and elsewhere. The deeper swelling is called angioedema. Angioedema may occur with or without urticarial weals (10%).

Rarely, urticaria results from an autoinflammatory disease such as systemic lupus erythematosus or Schnitzler syndrome, or an inherited condition such as Muckle-Wells syndrome or a cryopyrin-associated periodic syndrome.

Urticaria Angioedema
Image provided by Dr Shahbaz A Janjua
Urticaria
Urticaria & angioedema

More images of urticaria ...

Generalised ordinary urticaria

Generalized ordinary urticaria (hives) presents with spontaneous weals anywhere on the body. It is often classified according to how long it has been present. Ordinary urticaria is also known as spontaneous urticaria or idiopathic urticaria.

Urticaria may not be present all the time. Some find it more noticeable at certain times of day, or when they are warm or emotionally upset.

Acute urticaria is sometimes due to allergy. Allergy depends on previous exposure to the material, and the development of an immune reaction to it. An immunoglobulin called IgE is involved, which attaches itself to a receptor on the mast cell and causes it to release its chemical mediators.

The cause of an allergic urticaria may be:

Most allergies are mild, but very allergic individuals may develop serious anaphylactic shock within a few minutes of exposure. The most frequent causes are antibiotic injections, bee stings or ingestion of peanuts. Anaphylaxis results in urticaria, a tight chest, wheezing, faintness and collapse. Medical attention must be sought urgently. A subcutaneous adrenaline (epinephrine) injection will usually be given. Those prone to anaphylaxis should carry an emergency supply (e.g. an EpiPen™).

Most cases of urticaria are NOT due to allergy. Histamine and other vasoactive chemicals can be released into the skin for many reasons. In these cases urticaria can occur the first time that a person is exposed to the material.

Non-allergic causes of acute urticaria include:

Chronic urticaria is often due to autoimmune disease (allergy to one's self), and may be associated with other autoimmune conditions such as thyroid disease and coeliac disease. Circulating ‘anti-idiotypic’ antibodies can be detected in 10% of patients with chronic urticaria. These activate IgE bound on mast cells to cause excessive release of chemicals. More commonly there is no evidence for autoantibodies, and the patient is said to have chronic idiopathic urticaria. In most cases, chronic urticaria clears up, but 15% still have wealing at least twice weekly after 2 years.

Recurrent angioedema without urticaria may be due to C1 esterase deficiency (the protein C1 INH is missing or abnormal); there is often a family history of similar problems. It may also be caused by angiotensin converting enzyme (ACE) inhibitors such as captopril, quinapril, enalapril and others, which are used to treat heart failure and hypertension. These drugs inhibit kinin breakdown. Angioedema may also be idiopathic (of unknown cause).

Urticaria should be distinguished from urticarial vasculitis, in which weals persist for longer than 24 hours and vasculitis is found on skin biopsy. It results from immune complex deposition.

Physical urticaria

Physical urticaria refers to urticaria induced by external physical influences. The weals take about 5 minutes to develop, and last 15 to 30 minutes. Some people suffer from a mixture of different types of physical urticaria and generalized urticaria. The cause is unknown.

Dermographism means ‘skin writing’. Stroking the skin causes it to weal in the line of the stroke. This is very itchy, but scratching causes more wealing. Dermographism usually starts quite suddenly. Weals come up where clothes or furniture touch, especially when the affected person is hot or upset. A warm shower followed by rubbing with a towel can result in itchy weals all over.

Cholinergic urticaria results from sweating. In severe cases, hundreds of tiny red itchy spots develop after running, when warm, or when concentrating.

Cold urticaria affects skin warming up after a reduction in temperature, especially in winter. Weals can be widespread and may cause fainting attacks. Affected individuals should not expose large areas of the skin to the cold or wind. They should be advised never to swim alone.

Contact urticaria results from absorption of an elicting substance through the skin or through a mucous membrane. It may be allergic or non-allergic in origin. It may result in wealing confined to the site of contact or spreading more widely. IgE antibodies on mast cells react to chemicals in white flour, cosmetics, and textiles, or to proteins in latex rubber, saliva, meat, fish and vegetables may cause contact urticaria. Non-allergic examples include the stinging reaction of certain plants (e.g. nettles), animals (hairy caterpillar) and medicines.

Localised heat urticaria, aquagenic urticaria (water contact), solar urticaria (sunlight), vibratory angioedema and delayed pressure urticaria are less common.

Investigations in urticaria

In most cases of urticaria, there is no need for specific investigations. However, the following tests may be helpful in some cases.

Treatment of urticaria

Treatment depends on the type of urticaria, its severity and how long it has been present. If a medicine is thought to be the cause, it should be stopped.

Oral antihistamines control wealing and itching for the majority of patients with urticaria. The effective dose is variable. Antihistamines do not affect the underlying cause of the rash. They may need to be taken intermittently or continuously until the underlying tendency to urticaria disappears. Luckily, most people eventually recover.

Non-sedating antihistamines include:

Cetirizine is the quickest acting antihistamine, and desloratadine is the most long-lasting.

Conventional antihistamines such as chlorpheniramine or promethazine may be preferred at night as they tend to have a sedative effect. Hydroxyzine or diphenhydramine may be taken during the day and in some people they appear more effective than newer, non-sedating antihistamines.

Response and tolerance varies, so if the first antihistamine is not effective, consult your doctor. You may need to increase the dose up to four times (do this slowly in case of unexpected sedation), or use a different drug. Usually any sedative effect wears off in a week or so. Sometimes a combination of antihistamines works better than a single type alone.

Other treatments may be tried for urticaria that fails to clear with antihistamines. A combination of medicines may be required.

Intramuscular injection of adrenaline (epinephrine) is reserved for life-threatening anaphylaxis or swelling of the throat.

Desensitisation to certain essential medications has been reported to be effective in the case of urticaria caused by drug allergy. This involves careful monitoring with medical supervision in case the procedure causes anaphylaxis. A tiny dose of the drug is taken, with repeated and increasing doses over several hours to days.

General measures useful for urticaria

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