Urticaria Health Dictionary

A skin condition, also known as nettle rash or hives, that is characterized by the development of itchy weals, usually on the limbs and trunk. Large weals may merge to form irregular, raised patches.

Urticaria is generally harmless and usually lasts only a few hours. Sometimes a persistent or recurrent form develops. Dermographism is a less common form

of urticaria in which weals form after the skin is stroked. Urticaria sometimes occurs with angioedema.

The cause of urticaria is often unknown. The most common known cause is an allergic reaction (see allergy), often to a particular food, food additive, or drug. Urticaria may also be caused by exposure to heat, cold, or sunlight. Less commonly, it may be associated with another disorder, such as vasculitis, systemic lupus erythematosus, or cancer.

Itching can be relieved by applying calamine lotion or by taking antihistamine drugs. More severe cases may require corticosteroid drugs. Identifying and avoiding known trigger factors can help prevent future reactions. A tendency to urticaria often disappears in time without treatment.

Local itching of the skin – often results from an allergic reaction.

The rash produced by the sudden release of HISTAMINE in the skin. It is characterised by acute itching, redness and wealing which subsides within a few minutes or may persist for a day or more. Depending upon the cause, it may be localised or widespread and transient or constantly recurrent over years. It has many causes.

External injuries to the skin such as the sting of a nettle (‘nettle-rash’) or an insect bite cause histamine release from MAST CELLS in the skin directly. Certain drugs, especially MORPHINE, CODEINE and ASPIRIN, can have the same e?ect. In other cases, histamine release is caused by an allergic mechanism, mediated by ANTIBODIES of the immunoglobulin E (IgE) class – see IMMUNOGLOBULINS. Thus many foods, food additives and drugs (such as PENICILLIN) can cause urticaria. Massive release of histamine may affect mucous membranes – namely the tongue or throat – and can cause HYPOTENSION and anaphylactic shock (see ANAPHYLAXIS) which can occasionally be fatal.

Physical factors can cause urticaria. Heat, exercise and emotional stress may induce a singular pattern with small pinhead weals, but widespread ?ares of ERYTHEMA, activated via the AUTONOMIC NERVOUS SYSTEM (CHOLINERGIC urticaria) may also occur.

Rarely, exposure to cold may have a smiilar e?ect (‘cold urticaria’) and anaphylactic shock following a dive into cold water in winter is occasionally fatal. The diagnosis of cold urticaria can be con?rmed by applying a block of ice to the arm which quickly induces a local weal.

Transient urticaria due to rubbing or even stroking the skin is common in young adults (DERMOGRAPHISM or factitious urticaria). More prolonged deep pressure induces delayed urticaria in other subjects. IgE-mediated urticaria is part of the atopic spectrum (see ATOPY, and SKIN, DISEASES OF – Dermatitis and eczema). Allergy to peanuts is particularly dangerous in young atopic subjects. Notwithstanding the many known causes, chronic urticaria of unknown cause is common and may have an autoimmune basis (see AUTOIMMUNE DISORDERS).

Treatment Causative factors must be removed. Topical therapy is ine?ective except for the use of calamine lotion, which reduces itching by cooling the skin. Oral ANTIHISTAMINES are the mainstay of treatment and are remarkably safe. Rarely, injection of ADRENALINE is needed as emergency treatment of massive urticaria, especially if the tongue and throat are involved, following by a short course of the oral steroid, prednisolone.

Angio-oedema is a variant of urticaria where massive OEDEMA involves subcutaneous tissues rather than the skin. It may have many causes but bee and wasp stings in sensitised subjects are particularly dangerous. There is also a rare hereditary form of angio-oedema. Acute airway obstruction due to submucosal oedema of the tongue or larynx is best treated with immediate intramuscular adrenaline and antihistamine. Rarely, TRACHEOSTOMY may be life-saving. Patients who have had two or more episodes can be taught self-injection with a preloaded adrenaline syringe.

Itching, inflamed skin caused by an allergic reaction to a drug, food, or substance in the environment; also called hives

(nettle rash, hives) n. an itchy rash resulting partly from the release of *histamine by *mast cells. This causes either short-lived itchy *weals, deeper swellings (angio-oedema), or both. Individual weals typically appear rapidly and resolve spontaneously within hours. Acute urticaria is common and represents an immediate response to such allergens as seafood or nuts; it has been linked with upper respiratory tract infections, although many cases remain unexplained. Chronic urticaria is not an allergic condition and may persist for years. Angio-oedema occurs when the weals involve the deeper levels of the skin, resulting in swelling of the lips, eyes, or tongue, which may constitute a medical emergency. Urticaria can be treated by taking antihistamines regularly, but sometimes immunosuppressant treatment is needed, especially in autoimmune subtypes. Cholinergic urticaria is a condition in which very small weals are brought on by heat, exercise, or emotion; treatment is with antihistamines, but other drugs, including danazol, may be used for severe cases.

hives, nettle rash, acute or chronic affection of the skin characterized by the formation of weals, attended by itching, stinging or burning.