Urticaria is a common skin condition. It is also known as hives. Acute urticaria usually lasts from a few days up to six weeks. Chronic urticaria, by definition, lasts for more than six weeks. Urticaria normally appears without obvious triggers (“spontaneous urticaria”). Some patients may observe a physical stimulus to their symptoms (“inducible urticaria”). Spontaneous and inducible urticaria may appear in the same patients. A third form of urticaria, urticarial vasculitis, is uncommon and related to inflammation of blood vessels.
The redness and swelling are due to changes in the small blood vessels of the skin. This leads to increased blood flow to the affected skin, and excessive fluid moves into the surrounding tissues. Histamine is the predominant chemical causing these changes and it causes the sensation of itch. Histamine is released by the mast cell, a special type of immune cell in the skin. Mast cells release histamine when stimulated.
Urticaria appears as localised itchy skin swellings and these raised areas are also called wheals. They can affect any part of the body. The wheals may be pale, pink or red. They are usually circular, but can appear in different shapes and sizes. Each wheal usually resolves within 24 hours. However, new wheals may continue to erupt on other areas. Occasionally, swelling of the eyelids or lips may occur without any overlying redness of the skin. This is termed angioedema.
In urticarial vasculitis, the wheals may last for longer than 24 hours. They may also be more painful than itchy, and frequently go away leaving stains on the skin.
The cause of acute urticaria is frequently not found.
Known triggers include:
2. Viral infections
3. Contact e.g. chemicals, latex, cosmetics, plants, etc
Like acute urticaria, there is usually no readily identifiable cause for chronic urticaria. It has been found that some cases of chronic urticaria may be autoimmune in nature. These patients have antibodies targeting the mast cells leading to the release of histamine.
Inducible urticarias can be triggered by: physical pressure or friction on the skin, exercise, changes in skin temperature, vibration and sunlight.
Acute urticaria usually resolves after a few days or weeks. Chronic urticaria may last for months to years. Urticaria causes itch, which can be very distressing. It may cause significant disruption to the work and social life. In cases where angioedema is associated with urticaria, the airway may be affected. This can lead to breathing difficulties and immediate medical attention may be required.
The majority of people with urticaria are healthy. Urticaria is rarely associated with an underlying medical condition.
The diagnosis of urticaria can usually be made from the history and appearance, or description, of the hives. In the majority of people no cause can be found. Your doctor may ask you questions to try to identify one.
In acute urticaria, investigation is usually not necessary. Occasionally, if an allergic reaction is suspected, a specific blood test for allergic sensitization (RAST), or a skin prick test may be performed.
Chronic urticaria is rarely caused by allergy; so routine allergy tests are not necessary. A blood test may be necessary to ensure that there is no underlying medical condition such as thyroid disease or infection. In a small percentage of people, foods, colouring agents or preservatives 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. These substances can later be reintroduced to see if it aggravates the urticaria. When inducible urticaria is suspected, various challenge tests may be performed.
General measures include avoidance of known physical triggers, certain medications, alcohol, overtiredness, stress, maintenance of a cool environment, and light clothing.
Oral antihistamines are the main treatment for urticaria. They relieve itch and suppress hives. They do not affect the underlying cause of the rash. Antihistamines may need to be taken intermittently or continuously until the urticarial disappears. It is recommended that they be taken on a regular basis if frequent hives are experienced because regular dosing is more effective. The main side effect of anti-histamines is drowsiness. Non-sedating anti-histamines are available and these are frequently prescribed, especially during the day.
If patients do not respond to antihistamines, additional medications such as cyclosporin and omalizumab may be recommended by the doctor.
A short course of oral steroids may sometimes be prescribed in severe cases.