Urticaria is an itchy rash or skin eruption, characterised by weals (hives), which may occur anywhere on the body, or angioedema (swelling of the deeper layers of the skin). It is usually temporary, disappearing within 24 to 48 hours. Hives have many possible causes, including allergy.
- The rash has red weals (raised patches of skin) that often have skin-coloured centres. The weals may resemble mosquito bites.
- The rash is usually very itchy.
- Individual weals may come and go quite quickly — over hours.
- Weals may be a few millimetres in diameter or several centimetres.
- Weals may be round shaped or shaped like rings or maps.
- Weals may appear and fade repeatedly, in chronic urticaria.
- Weals may appear in response to triggers, such as exercise, cold or stress.
There are many causes of urticaria, including:
- an allergic reaction to drugs, food or preservatives;
- sweating (cholinergic urticaria);
- physical pressure;
- dermographism is a physical urticaria where firm stroking of the skin produces a red line which swells and becomes surrounded by a red flush of the nearby skin. There can be a weal down the line of the stroke. Dermographism literally means ‘writing on the skin’;
- infections, such as hepatitis or even a cold.
Often the cause of urticaria is not identified.
Tests and diagnosis
Urticaria is classified according to its duration:
- Acute urticaria: Less than 6 weeks’ duration.
- Chronic urticaria: More than 6 weeks’ duration with regular episodes of weals.
Most people don’t need tests for their urticaria. If the urticaria is chronic and has been occurring for a long time, then tests to identify an allergic cause may be needed.
Complications of a hives episode may include:
- Breathing difficulties, if swelling occurs in the mouth or throat. If this happens dial 000 and get help immediately.
- Anaphylactic shock: a serious allergic reaction where you have difficulty breathing, your blood pressure drops and you may feel dizzy or faint. Dial 000 and seek help immediately.
2. ASCIA. Urticaria (hives). Updated June 2010. http://www.allergy.org.au/patients/skin-allergy/urticaria-hives (accessed Aug 2015).