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<p><a class="external text" title="http://cougar.eb.com/soundc11/u/urtica01.wav" rel="nofollow" href="http://cougar.eb.com/soundc11/u/urtica01.wav"><strong>Urticaria</strong></a> (or <a class="external text" title="http://cougar.eb.com/soundc11/h/hives001.wav" rel="nofollow" href="http://cougar.eb.com/soundc11/h/hives001.wav"><strong>hives</strong></a>) is a skin condition, commonly caused by an allergic reaction, that is characterized by raised red skin <a title="Welt (medicine)" href="http://en.wikipedia.org/wiki/Welt_%28medicine%29">welts</a>. It is also known as <em><a title="Nettle" href="http://en.wikipedia.org/wiki/Nettle">nettle</a> rash</em> or <em>uredo</em>. Welts from hives can appear anywhere on the body, including the face, lips, tongue, throat, and ears. Welts may vary in size from about 5 mm (0.2 inches) in diameter to the size of a dinner plate; they typically <a title="Itch" href="http://en.wikipedia.org/wiki/Itch">itch</a> severely, sting, or burn, and often have a pale border. Urticaria is generally caused by direct contact with an allergenic substance, or an immune response to food or some other <a title="Allergen" href="http://en.wikipedia.org/wiki/Allergen">allergen</a>, but can also appear for other reasons, notably emotional stress. The rash can be triggered by quite innocent events, such as mere rubbing or exposure to cold.</p>
<p><a id="Pathophysiology" name="Pathophysiology"></a></p>
<h2><span class="mw-headline">Pathophysiology</span></h2>
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<p>The skin lesions of urticarial disease are caused by an inflammatory reaction in the skin, causing leakage of capillaries in the <a title="Dermis" href="http://en.wikipedia.org/wiki/Dermis">dermis</a>, and resulting in an <a title="Oedema" href="http://en.wikipedia.org/wiki/Oedema">oedema</a> which persists until the interstitial fluid is absorbed into the surrounding cells.</p><p>Urticarial disease is thought to be caused by the release of <a title="Histamine" href="http://en.wikipedia.org/wiki/Histamine">histamine</a> and other mediators of inflammation (cytokines) from cells in the skin. This process can be the result of an allergic or non-allergic reaction, differing in the eliciting mechanism of histamine release.</p>
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<div class="thumbinner" style="WIDTH: 152px"><a class="image" title="Allergic urticaria on the arm" href="http://en.wikipedia.org/wiki/Image:Urticaria_arm.jpg"><img class="thumbimage" height="200" alt="Allergic urticaria on the arm" width="150" border="0" src="http://upload.wikimedia.org/wikipedia/en/thumb/f/fa/Urticaria_arm.jpg/150px-Urticaria_arm.jpg" /></a>
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<div class="magnify" style="FLOAT: right"><a class="internal" title="Enlarge" href="http://en.wikipedia.org/wiki/Image:Urticaria_arm.jpg"><img height="11" alt="" width="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Allergic urticaria on the arm</div>
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<dl><dt>Allergic urticaria </dt><dd>Histamine and other pro-inflammatory substances are released from <a title="Mast cells" href="http://en.wikipedia.org/wiki/Mast_cells">mast cells</a> in the skin and tissues in response to the binding of <a title="Allergen" href="http://en.wikipedia.org/wiki/Allergen">allergen</a>-bound <a title="IgE" href="http://en.wikipedia.org/wiki/IgE">IgE</a> antibodies to high affinity cell surface receptors. Basophils and other inflammatory cells are also seen to release histamine and other mediators, and are thought to play an important role, especially in chronic urticarial diseases. </dd></dl><dl><dt>Non-allergic urticaria </dt><dd>Mechanisms other than allergen-antibody interactions are known to cause histamine release from mast cells. Many drugs, for example <a title="Morphine" href="http://en.wikipedia.org/wiki/Morphine">morphine</a>, can induce direct histamine release not involving any <a title="Immunoglobulin" href="http://en.wikipedia.org/wiki/Immunoglobulin">immunoglobulin</a> molecule. Also, a diverse group of signaling substances called <a title="Neuropeptides" href="http://en.wikipedia.org/wiki/Neuropeptides">neuropeptides</a> have been found to be involved in emotionally induced urticaria. Dominantly inherited cutaneous and neurocutaneous porphyrias (porphyria cutanea tarda, hereditary coproporphyria, variegate porphyria and erythropoietic protoporphyria) have been associated with solar urticaria. The occurrence of drug-induced solar urticaria may be associated with porphyrias. This may be caused by IgG binding not IgE. </dd></dl>
<p><a id="Urticaria_vs._poison_ivy_contact_dermatitis" name="Urticaria_vs._poison_ivy_contact_dermatitis"></a></p>
<h2><span class="editsection">[<a title="Edit section: Urticaria vs. poison ivy contact dermatitis" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=2">edit</a>]</span> <span class="mw-headline">Urticaria vs. poison ivy contact dermatitis</span></h2>
<p>The rash that develops from <a title="Poison ivy" href="http://en.wikipedia.org/wiki/Poison_ivy">poison ivy</a>, <a title="Poison oak" href="http://en.wikipedia.org/wiki/Poison_oak">poison oak</a>, and <a title="Poison sumac" href="http://en.wikipedia.org/wiki/Poison_sumac">poison sumac</a> contact is commonly mistaken for urticaria. This rash is caused by contact with <a title="Urushiol" href="http://en.wikipedia.org/wiki/Urushiol">urushiol</a> and results in a form of <a title="Contact dermatitis" href="http://en.wikipedia.org/wiki/Contact_dermatitis">contact dermatitis</a> called <a title="Urushiol-induced contact dermatitis" href="http://en.wikipedia.org/wiki/Urushiol-induced_contact_dermatitis">Urushiol-induced contact dermatitis</a>. Urushiol is spread by contact, but can be washed off with a strong grease/oil dissolving detergent and cool water.</p>
<p><a id="Types" name="Types"></a></p>
<h2><span class="editsection">[<a title="Edit section: Types" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=3">edit</a>]</span> <span class="mw-headline">Types</span></h2>
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<li><em>Acute urticaria</em> usually show up a few minutes after contact with the allergen and can last a few hours to several weeks. Food allergic reactions typically fit in this category. Common causes of reaction include consumption of <a title="Shellfish" href="http://en.wikipedia.org/wiki/Shellfish">shellfish</a>, <a title="Nut" href="http://en.wikipedia.org/wiki/Nut">nuts</a>, <a title="Egg (food)" href="http://en.wikipedia.org/wiki/Egg_%28food%29">eggs</a>, <a title="Fish" href="http://en.wikipedia.org/wiki/Fish">fish</a>, <a title="Acid" href="http://en.wikipedia.org/wiki/Acid">acid</a> derivatives, <a title="Dye" href="http://en.wikipedia.org/wiki/Dye">dye</a>, or a combination of these. </li>
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<p><a id="Related_conditions" name="Related_conditions"></a></p>
<h2><span class="editsection">[<a title="Edit section: Related conditions" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=4">edit</a>]</span> <span class="mw-headline">Related conditions</span></h2>
<p><a title="Angioedema" href="http://en.wikipedia.org/wiki/Angioedema">Angioedema</a> is related to urticaria. In angioedema, the swelling occurs in a lower layer of the dermis than it does in urticaria.<sup class="reference" id="_ref-0"><a title="" href="http://en.wikipedia.org/wiki/Urticaria#_note-0">[3]</a></sup> This swelling can occur around the mouth, in the throat, in the abdomen, or in other locations. Urticaria and angioedema sometimes occur together in response to an <a title="Allergen" href="http://en.wikipedia.org/wiki/Allergen">allergen</a> and is a concern in severe cases as angioedema of the throat can be fatal.</p>
<p><a id="Treatment_and_management" name="Treatment_and_management"></a></p>
<h2><span class="editsection">[<a title="Edit section: Treatment and management" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=5">edit</a>]</span> <span class="mw-headline">Treatment and management</span></h2>
<p>Urticarias can be very difficult to treat. There are no guaranteed treatments or means of controlling attacks, and some sub-populations are treatment resistant, with medications spontaneously losing their effectiveness and requiring new medications to control attacks. It can be difficult to determine appropriate medications since some such as <a title="Loratadine" href="http://en.wikipedia.org/wiki/Loratadine">loratadine</a> require a day or two to build up to effective levels, and since the condition is intermittent and outbreaks typically clear up without any treatment.</p>
<p>Most treatment plans for urticaria involve being aware of one's triggers, but this can be difficult since there are several different forms of urticaria and people often exhibit more than one type. Also, since symptoms are often <a title="Idiopathic" href="http://en.wikipedia.org/wiki/Idiopathic">idiopathic</a> there might not be any clear trigger. If one's triggers can be identified then outbreaks can often be managed by limiting one's exposure to these situations.</p>
<p><a id="Histamine_antagonists" name="Histamine_antagonists"></a></p>
<h3><span class="editsection">[<a title="Edit section: Histamine antagonists" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=6">edit</a>]</span> <span class="mw-headline">Histamine antagonists</span></h3>
<p>Drug treatment is typically in the form of <a title="Antihistamine" href="http://en.wikipedia.org/wiki/Antihistamine">Antihistamines</a> such as <a title="Diphenhydramine" href="http://en.wikipedia.org/wiki/Diphenhydramine">diphenhydramine</a>, <a title="Hydroxyzine" href="http://en.wikipedia.org/wiki/Hydroxyzine">hydroxyzine</a>, <a title="Cetirizine" href="http://en.wikipedia.org/wiki/Cetirizine">cetirizine</a> and other <a title="Histamine receptor" href="http://en.wikipedia.org/wiki/Histamine_receptor">H<sub>1</sub> receptor</a> antagonists.<sup class="reference" id="_ref-pmid18094952_0"><a title="" href="http://en.wikipedia.org/wiki/Urticaria#_note-pmid18094952">[4]</a></sup> These are taken on a regular basis to protective effect, lessening or halting attacks. While the disease is obviously physiological in origin, psychological treatments such as <a title="Stress management" href="http://en.wikipedia.org/wiki/Stress_management">stress management</a> can sometimes lessen severity and occurrence. Additionally, methods similar to psychological pain management can be used to shift focus away from the discomfort and itchiness during an attack.</p>
<p>The <a title="H2-receptor antagonist" href="http://en.wikipedia.org/wiki/H2-receptor_antagonist">H<sub>2</sub>-receptor antagonists</a> such as <a title="Cimetidine" href="http://en.wikipedia.org/wiki/Cimetidine">cimetidine</a> and <a title="Ranitidine" href="http://en.wikipedia.org/wiki/Ranitidine">ranitidine</a> may help control symptoms either <a title="Prophylactic" href="http://en.wikipedia.org/wiki/Prophylactic">prophylactically</a> or by lessening symptoms during an attack occurs.<sup class="reference" id="_ref-pmid11702618_0"><a title="" href="http://en.wikipedia.org/wiki/Urticaria#_note-pmid11702618">[5]</a></sup> When taken in combination with a H<sub>1</sub> antagonist it has been shown to have a synergistic effect which is more effective than either treatment alone.<sup class="noprint Template-Fact"><span title="This claim needs references to reliable sources since December 2007" style="WHITE-SPACE: nowrap">[<em><a title="Wikipedia:Citation needed" href="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed">citation needed</a></em>]</span></sup> The use of ranitidine (or other H<sub>2</sub> antagonist) for urticaria is considered an off-label use, since these drugs are primarily used for the treatment of <a title="Peptic ulcer" href="http://en.wikipedia.org/wiki/Peptic_ulcer">peptic ulcer</a> disease and <a title="Gastroesophageal reflux" href="http://en.wikipedia.org/wiki/Gastroesophageal_reflux">gastroesophageal reflux</a> disease.</p>
<p><a id="Other" name="Other"></a></p>
<h3><span class="editsection">[<a title="Edit section: Other" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=7">edit</a>]</span> <span class="mw-headline">Other</span></h3>
<p><a title="Tricyclic antidepressant" href="http://en.wikipedia.org/wiki/Tricyclic_antidepressant">Tricyclic antidepressants</a> such as <a title="Doxepin" href="http://en.wikipedia.org/wiki/Doxepin">doxepin</a>, also are often potent H<sub>1</sub> and H<sub>2</sub> antagonists and may have a role in therapy, although side effects limit their use. For very severe outbreaks, an oral <a title="Corticosteroid" href="http://en.wikipedia.org/wiki/Corticosteroid">corticosteroid</a> such as <a title="Prednisone" href="http://en.wikipedia.org/wiki/Prednisone">Prednisone</a> is sometimes prescribed. However this form of treatment is controversial because of the extensive side effects common with corticosteroids and as such is not a recommended long-term treatment option.</p>
<p>As of 2008 an <a title="Australia" href="http://en.wikipedia.org/wiki/Australia">Australian</a> company is performing <a title="Clinical trial" href="http://en.wikipedia.org/wiki/Clinical_trial">clinical trials</a> with an analogue of alpha-<a title="Melanocyte-stimulating hormone" href="http://en.wikipedia.org/wiki/Melanocyte-stimulating_hormone">melanocyte-stimulating hormone</a> called <a title="Melanotan" href="http://en.wikipedia.org/wiki/Melanotan">Melanotan</a> (CUV1647) for the treatment of solar urticaria,<sup class="reference" id="_ref-Australian_Life_Scientist_0"><a title="" href="http://en.wikipedia.org/wiki/Urticaria#_note-Australian_Life_Scientist">[6]</a></sup> a type of urticaria that develops in response to exposure to specific wavelengths of light.<sup class="reference" id="_ref-1"><a title="" href="http://en.wikipedia.org/wiki/Urticaria#_note-1">[7]</a></sup></p>
<p><a id="See_also" name="See_also"></a></p>
<h2><span class="editsection">[<a title="Edit section: See also" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=8">edit</a>]</span> <span class="mw-headline">See also</span></h2>
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<li><a title="Anti-itch drug" href="http://en.wikipedia.org/wiki/Anti-itch_drug">Anti-itch drug</a> </li>
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<p><a id="References" name="References"></a></p>
<h2><span class="editsection">[<a title="Edit section: References" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=9">edit</a>]</span> <span class="mw-headline">References</span></h2>
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<p><a id="External_links" name="External_links"></a></p>
<h2><span class="editsection">[<a title="Edit section: External links" href="http://en.wikipedia.org/w/index.php?title=Urticaria&action=edit&section=10">edit</a>]</span> <span class="mw-headline">External links</span></h2>
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<li><a class="external text" title="http://www.users.globalnet.co.uk/~aair/urticaria.htm" rel="nofollow" href="http://www.users.globalnet.co.uk/~aair/urticaria.htm">Urticaria conditions and descriptions</a> </li>