Hives

Hives, also known as urticaria, is a kind of skin rash with red or flesh-colored, raised, itchy bumps. Hives may burn or sting. The patches of rash may appear on different body parts, with variable duration from minutes to days, and typically do not leave any long-lasting skin change. Fewer than 5% of cases last for more than six weeks (a condition known as chronic urticaria). The condition frequently recurs.

Hives frequently occur following an infection or as a result of an allergic reaction such as to medication, insect bites, or food. Psychological stress, cold temperature, or vibration may also be a trigger. In half of cases the cause remains unknown. Risk factors include having conditions such as hay fever or asthma. Diagnosis is typically based on appearance. Patch testing may be useful to determine the allergy.

Prevention is by avoiding whatever it is that causes the condition. Treatment is typically with antihistamines, with the second generation antihistamines such as fexofenadine, loratadine and cetirizine being preferred due to less risk of sedation and cognitive impairment. In refractory (obstinate) cases, corticosteroids or leukotriene inhibitors may also be used. Keeping the environmental temperature cool is also useful. For cases that last more than six weeks, long-term antihistamine therapy is indicated. Immunosuppressants such as omalizumab or cyclosporin may also be used.

About 20% of people are affected at some point in their lives. Short duration cases occur equally in males and females, lasting a few days and without leaving any long-lasting skin changes. Long duration cases are more common in females. Short duration cases are also more common among children, while long duration cases are more common among those who are middle-aged. Hives have been described since at least the time of Hippocrates. The term urticaria is from the Latin urtica meaning "nettle".

Hives, or urticaria, is a form of skin rash with red, raised, itchy bumps. They may also burn or sting. Hives can appear anywhere on the surface of the skin. Whether the trigger is allergic or not, a complex release of inflammatory mediators, including histamine from cutaneous mast cells, results in fluid leakage from superficial blood vessels. Hives may be pinpoint in size or several inches in diameter, they can be individual or confluent, coalescing into larger forms.

Angioedema is a related condition (also from allergic and nonallergic causes), though fluid leakage is from much deeper blood vessels in the subcutaneous or submucosal layers. Individual hives that are painful, last more than 24 hours, or leave a bruise as they heal are more likely to be a more serious condition called urticarial vasculitis. Hives caused by stroking the skin (often linear in appearance) are due to a benign condition called dermatographic urticaria.^{[citation needed]}

Hives can also be classified by the purported causative agent. Many different substances in the environment may cause hives, including medications, food and physical agents. In perhaps more than 50% of people with chronic hives of unknown cause, it is due to an autoimmune reaction. Risk factors include having conditions such as hay fever or asthma.

Drugs that have caused allergic reactions evidenced as hives include codeine, sulphate of morphia, dextroamphetamine, aspirin, ibuprofen, penicillin, clotrimazole, trichazole, sulfonamides, anticonvulsants, cefaclor, piracetam, vaccines, and antidiabetic drugs. The antidiabetic sulphonylurea glimepiride, in particular, has been documented to induce allergic reactions manifesting as hives.^{[citation needed]}