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.
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.
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:
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.
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:
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.
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.
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:
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.
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:
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.
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: