The rash produced by the sudden release of HISTAMINE in the skin. It is characterised by acute itching, redness and weals 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.
such as the sting of a nettle (‘nettle-rash’) or an insect bite cause histamine release from MAST CELLS in the skin. Certain drugs, especially MORPHINE, CODEINE and ASPIRIN, can have the same effect. 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.
can cause urticaria. Heat, exercise and emotional stress may induce a singular pattern with small pinhead weals, but widespread flares of ERYTHEMA, activated via the AUTONOMIC NERVOUS SYSTEM (CHOLINERGIC urticaria) may also occur.
Rarely, exposure to cold may have a similar effect (‘cold urticaria’), the diagnosis being confirmed 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). Notwithstanding the many known causes, chronic urticaria of unknown cause is common and may have an autoimmune basis (see AUTOIMMUNE DISORDERS).
Causative factors must be removed. Topical therapy is ineffective except for the use of calamine lotion, which reduces itching by cooling the skin. Oral ANTIHISTAMINES are the mainstay of treatment. 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.
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.