What is urticaria?

Urticaria, also known as hives or nettlerash, is an itchy, painful, rash with patches of raised red or white skin (known as wheals). It is caused by fluid leaking from blood vessels in the skin. Urticaria is classed into acute urticaria (which lasts for only a short period of time) and chronic urticaria (which lasts longer). There are also different types of urticaria, which may be chronic or acute. These include: contact urticaria (which is caused by something touching the skin), urticarial vasculitis (which has wheals that last longer than 24 hours, often with burning or pain), and physical urticaria (which has several different subtypes). Urticaria may occur with angioedema, which is swelling due to fluid building up, and typically affects the lips, face, and throat.

What do the wheals of urticaria look like?

The wheals in urticaria are often a pinky-red, but may have a paler centre. They can range in size from a few millimetres to a few centimetres, and can occur anywhere on the body. They are usually circular, but wheals which are close to each other can fuse to form many different irregular shapes. These wheals can be itchy, but are often relieved by rubbing rather than scratching. Usually, these wheals only last a few hours.

Approximately 15 % of people get urticaria every year.

What is acute urticaria?

Acute urticaria is urticaria lasting less than 6 weeks, with individual wheals usually lasting less than 24 hours. Acute urticaria is more common in children than adults, and studies have found a number of causes:

  • No cause can be found in 50 % of people with urticaria.
  • 40 % of urticaria can be caused by upper respiratory tract infections, such as the common cold, flu, coughs etc.
  • 9 % of urticaria can be caused by various drugs, such as certain types of antibacterial drugs, muscle relaxants, and certain types of painkillers.
  • Only 1 % of urticaria is caused by foods. However, the actual figure may be a little higher than 1 %. Common foods include fish and seafood, eggs, dairy, and nuts.

Between 20 % and 30 % of people with acute urticaria go on to develop chronic urticaria at some point in their lives. Acute urticaria may not require treatment as it is not usually serious. However, a bath or shower might help ease the itching, and antihistamines such as loratadine or cetirizine hydrochloride might be able to ease some of the symptoms too.

What is chronic urticaria?

Chronic urticaria lasts longer than 6 weeks. The wheals appear regularly (usually daily), and the individual wheals usually last between 4 and 6 hours. Chronic urticaria is also twice as common in women than in men.

In the majority of cases, the cause is not known. In 35 - 50 % of cases, the problems may be due to the body's own defence mechanisms causing the blood vessels to become leaky. Drugs such as aspirin and certain other painkillers can alter body chemistry and also cause chronic urticaria. Food allergies rarely cause chronic urticaria.

A bacteria known as Helicobacter pylori (which causes peptic ulcers in the stomach) may indirectly cause chronic urticaria. In addition, chronic urticaria might run in some families. Intestinal parasites such as roundworms can also cause chronic urticaria.

There are several diseases in which the body's immune system attacks parts of the body that are associated with chronic urticaria. They include:

  • Graves' disease and Hashimoto's thyroiditis - conditions in which the immune system. attacks the thyroid gland, an important part of the body involved with metabolism.
  • Vitiligo - a disease where white or pale patches appear on the skin.
  • Rheumatoid arthritis - a condition where the body's immune system attacks joints (particularly those in the fingers), leading to pain in the joints.
  • Pernicious anaemia - a condition where vitamin B12 cannot be absorbed into the body.
  • Insulin-dependent diabetes mellitus - a disease where the immune system attacks certain cells in the pancreas involved in regulating the amount of sugar in our blood.

Treatment for chronic urticaria involves antihistamines and possibly H2-blockers (which act on histamine receptors) such as ranitidine or cimetidine. If any particular trigger can be identified, that should be avoided as well to prevent future episodes.

What is contact urticaria?

Contact urticaria develops where the skin or body surface has been touched by something. There are allergic and non-allergic types, the difference between the two is in how the body reacts to the substance causing the urticaria. In allergic cases, it is because the body has become sensetised to a particular substance such as grass or foods or latex. Non-allergic contact urticaria happens when certain chemicals directly act on blood vessels. These chemicals may include chemicals in cosmetics, eye solutions, and nettle stings.

What is urticarial vasculitis?

Urticarial vasculitis differs from urticaria in that the wheals tend to last longer than 24 hours. They can also be associated with burning and pain in addition to itching. Urticarial vasculitis is relatively rare - it is estimated to affect 1 - 10 % of people with chronic urticaria. It is usually part of another disease affecting the whole body, such as:

  • Systemic lupus erythematosus - a condition where the skin and various internal organs become inflamed. It typically presents with a “butterfly rash,” which covers the cheeks and bridge of the nose.
  • Sjörgen's syndrome - a disease where glands are affected, leading to a dry mouth, eyes, throat, and dryness in other areas.

What are physical urticarias?

Physical urticarias occur in response to certain stimuli and occur only in those areas affected by those stimuli. The wheals tend to resolve within 2 hours.

Dermatographism is the most common physical urticaria. In dermatographism, wheals develop over parts of skin that are stroked firmly. Dermatographism isn't associated with any form of allergy or atopy, food, autoimmunity (where the body's immune system attacks parts of the body), or any other diseases.

Cholinergic urticaria is the second most common form of physical urticaria. Wheals form in response to exercise, stress, or emotions, and are surrounded by a reddened flare on the skin. Adrenergic urticaria, on the other hand, has wheals which are small and pink and surrounded by paler skin.

Delayed pressure urticaria develops on parts of the body which have had pressure applied to them for a long period of time. The wheals can develop after 30 minutes or even as long as 12 hours after the pressure has been lifted. Common areas are around the waist after wearing a tight pair of trousers or a tight belt, or at the ankles or lower leg where the top of socks are.

Other types of physical urticarias can occur in response to water, sunlight, cold, or pressure.

What is angioedema?

Angioedema is a swelling caused by fluid leaking from blood vessels. It is usually caused as a result of allergy, and common triggers include foods and insect stings. Other causes of angioedema include:

  • Heat, cold, or vigorous exercise (angioedema caused by these factors is associated with physical urticarias)
  • Drugs, such as aspirin, certain types of painkillers, anti-inflammatory drugs, and ACE inhibitors like enalapril.
  • Physical injury can cause angioedema in people with hereditary angioedema (C1 inhibitory deficiency). In these cases, the swelling can last from a few hours to a few days. Often, there is no accompanying urticaria, and antihistamines do not work against it. Angioedema can also be spontaneous in people with hereditary angioedema.

The lips, face, genitalia, extremities, throat, and tongue are often affected - angioedema in the tongue or throat can cause a blockage in the airways and can be fatal. Angioedema can also affect the gut, and here it can lead to symptoms such as severe abdominal pain.

Angioedema is treated with oral antihistamines such as loratadine. However, this is ineffective in people with hereditary angioedema or angioedema caused by ACE inhibitors. The swelling usually subsides in several hours. If someone gets a blockage of their airways because of angioedema, seek urgent medical help.

How can urticaria be diagnosed?

Urticaria can be diagnosed easily clinically by talking to the patient and finding out what the rash is like. However, there are a number of investigations that can help doctors to find out what type of urticaria you have and what might possibly be causing it. They include:

  • Blood tests. Blood tests would look for many different things. Doctors might look for eosinophils in your blood - eosinophils are a type of white blood cell which defend your body against parasites, and more eosinophils are found when parasites are in the body. Doctors might also look for IgE, a chemical involved in allergy, and might try to find out what you are allergic to using your IgE (this test is known as a RAST). Doctors might also look for various other proteins involved in inflammation and immunity.
  • A test known as erythrocyte sedimentation rate (ESR) can be useful in detecting the presence of any infections or inflammation.
  • Investigations which look at how well your liver and kidneys are working. This can reveal any underlying diseases which might be causing or contributing to your urticaria.
  • A biopsy of the skin might be useful if doctors think you might suffer from urticarial vasculitis. A biopsy of the skin involves taking a small sample of skin from your body and looking at it under a microscope.
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