Urticaria is characterised by wheals (hives), which are superficial red skin swellings lasting a few minutes to 24 hours, and are usually very itchy. Urticaria can be acute (< 6 weeks in duration) or chronic (> 6 weeks in duration, regular occurrence).
The redness and swelling are due to changes in small blood vessels of the skin. Histamine, a chemical which causes itch, is released into the skin, causing localised skin swellings. Any part of the body can be affected, and they usually resolve within 24 hours. However, new wheals may continue to erupt on other areas.
The cause is frequently not found. Some known triggers include:
Sometimes, urticaria is caused by a physical stimulus on the skin. Examples of physical stimuli are physical pressure on the skin, exercise, cold temperature and sunlight.
It is generally not dangerous, except in situations where swelling of the airway is associated with urticaria. If you feel a lump in the throat, with difficulty breathing, emergency medical attention is needed.
The diagnosis of urticaria can usually be made from the history and appearance, or description of the hives. It is useful to take a photo of the hives when they appear. In the majority of people no exact cause can be found. In a small percentage of people, certain food may appear to worsen the urticaria. A food diary may be kept and the suspected substances can be omitted from the diet to see if the condition improves. If an allergic reaction is suspected, a specific blood test for allergic sensitisation (RAST), or a skin prick test may be performed.
For chronic urticaria, blood tests may be necessary to ensure that there is no underlying medical condition such as thyroid disease or infection.
Treatment depends on the type of urticaria you have. Anti-histamines may be given in a specified manner to stop the allergic reaction. Non-sedating new generation anti-histamines are available. If the condition does not respond to anti-histamines, newer effective biologic medicines such as omalizumab (Xolair) are available. Speak to your dermatologist regarding your suitability for this treatment.