Urticaria results from the release of histamine, bradykinin, leukotriene C4, prostaglandin D2, and other vasoactive substances from mast cells and basophils in the dermis.  These substances cause extravasation of plasma into the dermis, leading to the urticarial lesion. The intense pruritus of urticaria is a result of histamine released into the dermis. One study showed that D-dimer levels correlate with the severity of acute urticaria and may serve as a marker of disease severity. 
It is typically diagnosed when chronic hives do not appear to be associated with any other systemic disease process, and are not due to one of the physically induced urticarias. Research during the past decade suggests an association with autoimmunity in 35-45% of patients. When severe, it can be resistant to therapy and there is a 40% incidence of accompanying angioedema. Angioedema may involve the face, lips, tongue, throat, or extremities but not the larynx. The remission rate is 65% within three years, 85% within five years and 98% within ten years. A form of angioedema in the absence of hives with no identifiable cause is termed idiopathic angioedema.
Professional Reference articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use. You may find the Hives (Chronic Urticaria) article more useful, or one of our other health articles.
The most common food allergies in adults are shellfish nuts. The most common food allergies in children are shellfish, nuts, eggs, wheat, and soy. One study showed Balsam of Peru, which is in many processed foods, to be the most common cause of immediate contact urticaria. A less common cause is exposure to certain bacteria, such as Streptococcus species or possibly Helicobacter pylori.
About 20% of people are affected. Cases of short duration occur equally in males and females while cases of long duration are more common in females. Cases of short duration are more common among children while cases of long duration are more common among those who are middle aged. Hives have been described at least since the time of Hippocrates. The term urticaria is from the Latin urtica meaning “nettle”.
Mortureux P, Léauté-Labrèze C, Legrain-Lifermann V, Lamireau T, Sarlangue J, Taïeb A. Acute urticaria in infancy and early childhood: a prospective study. Arch Dermatol. 1998 Mar. 134(3):319-23. [Medline].
The emotional impact of urticaria and its effect on quality of life should also be assessed. The Dermatology Life Quality Index (DLQI) and CU-Q2oL, a specific questionnaire for chronic urticaria, have been validated for chronic urticaria, where sleep disruption is a particular problem.
If any features of anaphylaxis (eg, hypotension, respiratory distress, stridor, gastrointestinal distress, swallowing problems, joint swelling, joint pain) are present, immediate medical intervention should occur. (See Physical Examination.)
If you have chronic hives, or urticaria, you probably already know that when you are under stress, your symptoms either appear or worsen. Doctors have increasingly looked to study the relationship between emotional stress and skin conditions. One study, which appeared in Dermatology Times, examined the relationship between stress and chronic hives. Josie Howard, M.D., a psychiatrist in private practice and clinical instructor of psychiatry and dermatology at the University of California, stated that, “external stressors plus cognitive, behavioral and social stressors have been shown to play a significant role in the intensity of itch.” She also explains that it is not unusual for hives to appear after a major life stressor and that those with chronic hives have “limited stress management skills.”
4. Rockwell WJ. Reactions to molds in foods. In: Chiaramonte LT, Schneider AT, Lifshitz F, editors. Food allergy: a practical approach to diagnosis and management. New York: Marcel Dekker; 1988. pp. 153–70.
The initial medical treatment for urticaria is a standard dose of a second-generation H1 anti-histamine. These drugs penetrate the blood–brain barrier to only a slight extent and so cause fewer central nervous system side effects than the older first-generation anti-histamines, although symptoms such as sedation and psychomotor impairment may still occur. Seven such anti-histamines are licensed for use in the United Kingdom: Cetirizine, desloratidine, fexofenadine, levocetirizine, loratidine and mizolastine, which are all given once a day, and acrivastine which is given three times a day, and may therefore be less effective and convenient to use. Cetirizine and levocetirizine  and loratidine  may have clinically useful ‘anti-inflammatory’ properties at therapeutic doses. Cetirizine may cause drowsiness in some patients and mizolastine is contra-indicated in patients with cardiac disease; prolonged Q-T interval; or severe liver disease. Dose reductions may be needed if there is renal impairment. Clinical response and tolerability may be better with one second-generation H1 anti-histamine than another, so if symptoms are not well controlled or the patient notices side effects with the first drug chosen, a second drug should be tried. Often, symptom control is improved if the dose of anti-histamine is increased to twice daily. This is above the licensed recommended dose; however, ‘off-label’ dosages are recommended widely [44,45,51]. A night-time dose of one of the older first-generation, sedating H1 anti-histamines, such as chlorphenamine or hydroxyzine, may help patients to sleep. Empirically, anti-histamine treatment is usually prescribed for 3–6 months (or longer if the patient has angioedema associated with the urticaria) and is tailed off gradually. Episodic urticaria may be treated with stat doses of anti-histamines as required.
The band members contributed to “Time For Some Action” and “Windows” on N.E.R.D.’s “Seeing Sounds” album, with Pelle Almqvist providing guest vocals on “Time For Some Action”. On Seeing Sounds they are credited with their real names instead of the pseudonyms they use within the band.
68. Diav-Citrin O, Shechtman S, Aharonovich A, et al. Pregnancy outcome after gestational exposure to loratadine or antihistamines: a prospective controlled cohort study. J Allergy Clin Imunol. 2003;111:1239–43. [PubMed]
Hives are a very itchy rash usually caused by an allergic reaction. Hives look like raised pink spots with pale centers on the skin. The spots range from 1/2 inch to several inches wide (hives often look like mosquito bites). The spots may be different shapes. The spots rapidly and repeatedly change in location, size, and shape. Giant hives are called angioedema. This can cause large swelling beneath the skin, especially of the face.
37. Sabroe RA, Fiebiger E, Francis DM, et al. Classification of anti-FcepsilonRI and anti-IgE autoantibodies in chronic idiopathic urticaria and correlation with disease severity. J Allergy Clin Immunol. 2002;110:492–9. [PubMed]
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Mastocytosis is a disease in which there is mast cell hyperplasia affecting the skin, gastrointestinal tract, bone marrow, liver, spleen and lymph nodes. Clinical features include urticaria, pruritus, flushing, nausea, vomiting, abdominal pain, diarrhoea and headache. Patients may be prone to severe anaphylactoid reactions after exposure to certain medications  and severe anaphylactic reactions after exposure to antigens to which they are sensitized, such as insect venom , because of the increased tissue load of mast cells. Mastocytosis is classified into cutaneous and systemic variants and urticaria pigmentosa is the most common form of cutaneous mastocytosis, occurring in approximately 85% of children and 95% of adults in whom mastocytosis is limited to the skin. Systemic mastocytosis varies from an indolent condition, where there is no associated haematological disease, to an aggressive mast cell leukaemia. The lesions of urticaria pigmentosa are variable in colour, macular or maculopapular and are usually symmetrical in distribution, with sparing of the extremities and face. The diagnosis of urticaria pigmentosa is made by skin biopsy, which shows a significant increase in dermal mast cells . Patients have symptoms of pruritus and dermographism and pressure on affected skin causes erythema and urtication –‘Darier’s sign’. Children usually present before the age of 2 years and urticaria pigmentosa may be present at birth. They tend to have fewer, larger skin lesions than adults and they may also develop bullae, which do not occur in adults. Treatment is with H1 and H2 anti-histamines and ketotifen  (an anti-histamine with mast cell-stabilizing properties), methoxsalen with long-wave ultraviolet radiation (psoralen plus ultraviolet A,)  and topical steroids  may all be used to alleviate urticaria and pruritus. It is rare for children to develop systemic mastocytosis and urticaria pigmentosa resolves completely in about 50% of children. In contrast, urticaria pigmentosa in adults usually persists and about 50% of patients may go on to develop systemic mastocytosis. The prognosis in adults is, therefore, highly variable.
Non-sedating antihistamines that block the histamine H1 receptors are the first line of therapy. First generation antihistamines such as diphenhydramine or hydroxyzine block both central and peripheral H1 receptors and can be sedating. Second generation antihistamines such as loratadine, cetirizine, or desloratadine selectively antagonize the peripheral H1 receptors and are less sedating, less anticholinergic, and generally preferred over the first generation antihistamines.
Theoretically, almost any drug can cause an allergic reaction (see the images below); thus, allergic reactions to a wide variety of drugs can occur. Antibiotics, such as penicillin, have been implicated most frequently.  Urticarial reactions to penicillin can occur as long as 14 days after a course of treatment has stopped. In this situation, serum sickness may be present.
The rash may be triggered by an allergy, or by another factor such as heat or exercise. In most cases the rash lasts 24-48 hours and is not serious. You may not require any treatment; however, medicines called antihistamines can ease the symptoms until the rash clears.
Urticaria results from the release of histamine, bradykinin, leukotriene C4, prostaglandin D2, and other vasoactive substances from mast cells and basophils in the dermis.  These substances cause extravasation of plasma into the dermis, leading to the urticarial lesion. The intense pruritus of urticaria is a result of histamine released into the dermis. One study showed that D-dimer levels correlate with the severity of acute urticaria and may serve as a marker of disease severity.