Urticaria is often referred to as nettle rash or hives. The disorder causes wheals in the skin.
The weals can be a few millimetres or several centimetres diameter, coloured white or red, often surrounded by a red flare, and usually itchy. Each wheal may last a few minutes or several hours, and may change shape. Wheals may be round, or form rings, a map-like pattern, or giant patches.
Involvement of the face may cause swelling of the eyelids and lips. The wheals and swellings occur because of the release of chemicals, such as histamine, into the tissues. This causes small blood vessels to leak fluid into the skin.
There are various different types of urticaria, which can be classed as "acute", meaning it has only been present recently (hours, days or a few weeks), or "chronic", meaning it has persisted for several months or even years. Wheals may not be present all the time, often being more noticeable at certain times of day or when hot.
People often associate acute urticaria with an allergic reaction. Typically, medicines such as antibiotics, or food, including even tiny amounts of fish, eggs, nuts or chocolate, are responsible. It depends on previous exposure to the material, and the development of an immune reaction to it.
Although most have a mild reaction affecting only the skin, rarely very allergic individuals develop the much more severe condition called " anaphylaxis".
In such cases, the cause is usually obvious - an antibiotic injection, a bee sting, ingestion of peanuts - a few minutes earlier. The urticarial rash is accompanied by a tight chest, wheezing, faintness and collapse. Medical attention must be sought urgently. An adrenaline injection may be needed to treat this.
Most cases of urticaria are probably not due to an allergy. Sometimes medicines (morphine, codeine, quinine, aspirin and other non-steroidal anti-inflammatory drugs) and foods (azo dyes, benzoates) cause the rash . A small dose may be tolerated, but a large dose causes hives. Urticaria can occur the first time a person has a particular medicine or food.
In most cases, urticaria settles quickly. Unfortunately, a few people develop chronic urticaria. It is thought that this may be due to an autoimmune disease. Circulating antibodies cause excessive release of histamine. Most individuals with chronic urticaria are otherwise healthy but a few have another autoimmune condition such as thyroid disease.
Physical urticaria refers to urticaria caused by external physical influences such as heat, cold, contact with chemicals, plants e.g. nettles. The wheals of a physical urticaria usually take about 5 minutes to develop, and last 15 to 30 minutes. Each type may occur alone, or with other types of physical urticaria, or with acute or chronic generalized urticaria. The commonest physical urticaria is dermographism. Stroking the skin causes it to weal in the line of the stroke, This is very itchy, causing the individual to scratch, which makes the whealing worse. The wheals may come up where clothes or furniture touch. Dermographism usually starts quite suddenly. It tends to be more severe when the affected person is hot or upset. A warm shower followed by rubbing with a towel can result in itchy weals all over.
If you have urticaria, you may need to seek the advice of your doctor.
In most cases, treatment with oral antihistamines is very effective and controls the whealing and itching. Antihistamines are not a cure, and so they may need to be continued until the underlying tendency to the rash disappears. Many people need antihistamines only occasionally. Whenever possible, choose one of the newer non-sedating antihistamines (loratadine, fexofenadine, cetirizine) as these are less likely to cause drowsiness. They may be unsuitable in pregnancy In some cases, steroids by mouth may be prescribed for severe acute urticaria. Steroids are unsuitable long term because of side effects.
If you have generalized urticaria, ask your doctor if a medicine could be the cause. Avoid aspirin and codeine, and reduce your intake of acidic fruits. Don't consume food or confectionary containing tartrazine (a yellow dye, numbered E102 in the list of ingredients on the container), or meats preserved with benzoates (E210-E220). Also avoid alcohol.
Try not to overheat. Cool the affected area with a cold flannel or ice-pack.
This article published on
01 July 2005
Next review date 9/1/2013
Skin, hair and bones
Skin, hair and bones