Hives, also known as urticaria, is a skin condition where there are reddish, itchy and raised plaques on the surface of the skin. It appears anywhere on the body and can migrate from one location to another on the skin. Women are more commonly affected. Hives may be accompanied by swelling beneath the surface of the skin (angioedema).
Hives are classified by the duration it persists. Acute hives typically disappears within a couple of months and are more common than chronic hives. It may however, recur at any time. Chronic hives stay on for more than 2 months. Usually, hives do not have any long-term complications. However, the accompanying angioedema could be life-threatening if the swollen tongue and throat cause obstruction of breathing.
The common symptoms associated with hives includes:
- Reddish, raised plaques of various sizes and shapes appear rapidly on the skin.
- The hives turn white when pressed at the center (a phenomenon known as blanching).
- There is itching in the plaques.
- The plaques may disappear from one place and then reappear at another place on the skin, often within a few hours.
- Swelling of face, lips, hands, feet, throat, and genitals (due to angioedema) may accompany hives.
There are no diagnostic tests for hives. The diagnosis is made on the basis of skin examination and history of the condition. One of the main factors that help in diagnosis of hives is the fact that the skin symptoms are not stable and change with time, even within a span of a few hours.
Hives are caused by the activation of mast cells and basophils in the skin and blood, respectively. These are immune cells that mediate the inflammatory process intended to reduce damage to tissue. However, in this condition it is triggered despite the lack of damage to the tissue. Activated mast cells and basophils release various substances (such as histamine, bradykinin and kallikrein) that increase the permeability of blood vessels. Leaking of fluid and entry of other immune cells from the blood vessels leads to the symptoms associated with hives.
Activation of mast cells can be caused by both allergic and non-allergic triggers.
Some cases of hives (especially acute hives) are thought to be triggered by allergic reactions to certain foods, medicines, infections or insect bites. An autoimmune disease, in which the body produces antibodies against its own cells, may also trigger mast cell activation (e.g., by making antibodies against the receptors on the mast cells).
Non-allergic triggers could be drugs, various physical factors (sunlight, water, cold, heat, pressure, exercise) and emotional stimuli (stress, anxiety). In many cases, however, the precise cause of hives remains unknown.
Hives usually goes away spontaneously. Treatment is mostly aimed at reducing the symptoms of itching and swelling. Anti-histamines (diphenhydramine, loratadine, cetrizine) are the main medications given for hives. They prevent the symptoms caused by histamine release. Drowsiness is a typical side-effect of taking anti-histamine medications. Some newer anti-histamines (loratadine, fexofenadine) do not cause drowsiness. Many of these anti-histamine medications are available as over-the-counter drugs that do not require prescription.
Corticosteroids are given in cases where the symptoms are severe. In some people the allergic trigger of hives could cause anaphylactic shock and death. In such cases, emergency treatment with adrenaline injections should be given. In cases where the cause of hives can be established, the treatment is directed at removing the cause.