What is Urticaria ?
Urticaria is a sudden skin eruption, which involves redness, localised swelling, and often in a circular, oval or ‘map’ shape which can be quite patchy. In tends to occur on the trunk, arms and legs, but can occur anywhere. Pressing the affected area will cause the areas to blanch. Often they change in position and shape and sometimes can be quite large. The rash is due to sudden dilatation of capillaries and release of chemicals just under the skin. Histamine is often involved and these inflammatory chemicals are released by mast cells.
Causes and Types of Urticaria
- Common acute urticaria: This is by far the most common type seen in children. It can occur at any age and may or may not be associated with a viral illness. It may or may not be itchy. It lasts a few days, and will come and go until eventually disappearing. Other than the rash the child is not particularly unwell, though they may have a low grade temperature or an upper respiratory tract infection. There is generally no treatment apart from some antihistamine, and it is not infectious.
- Acute allergic reaction – Occasionally urticaria is part of an allergic reaction. In this instance there generally be an obvious ‘trigger’ such as a new food or medication. The rash will be one part of an acute reaction.
- Food – peanuts, tree nuts, fish, shellfish are the most common culprits and urticaria is part of the allergic reaction which may involve gastrointestinal, respiratory, symptoms. It can be part of anaphylaxis. Usually the reactions occur within minutes of ingesting the food.
- Medications – The most common are antibiotics and anti inflammatory medications. The urticaria can occur quickly or sometimes a few days later.
- Sometimes local toxins such as insect bites or contact with plants will cause urticaria at the site of contact. Jellyfish sting is a classic example.
- Other types of urticaria –
- Chronic urticaria – lasts for 6 weeks and is more suggestive of an underlying medical problem
- Papular urticaria – occurs where there are a number of insect bites. Dotted small areas of hives on arms and legs, can often become itchy and secondarily infected.
- Physical urticaria is due to pressure or temperature. Some urticaria can be triggered by cold or heat in some people.
- Idiopathic – means that there is no cause identified. This is probably one of the most common.
Are any tests needed ?
In most cases there is no need for testing unless the history suggests an acute allergic reaction or the urticaria is quite severe. Most cases can be determined by a careful history or examination. In severe urticaria the child will be unwell, with high fever and the urticaria will be extensive and last for days. This particular type is rare but will need assessment by paediatrician or emergency department.
What treatment is available ?
The cornerstone of treatment is time. Antihistamines are sometimes useful and can be obtained over the counter without a prescription. In severe cases a course of steroids is occasionally required. Creams and ointments are of little use as the skin itself is not inflamed. But keeping the child cool will help if there is itching.