Initial Evaluation

Acute urticaria

  • Migrating pruritic edematous papules and plaques of variable size, surrounded by erythema or an area of vasoconstriction (i.e., wheal).
  • Can be intermittent, with the skin returning to normal appearance in less than 24 hours.
  • Causes include drug reactions, food allergy, systemic disorders, and infection.
  • The underlying cause may be undetermined in many cases.
  • The majority of acute reactions resolve within days to weeks.
  • Therapy is symptomatic and attempts to suppress symptoms until urticaria abates.

Chronic urticaria

  • Defined as urticaria lasting longer than 6 weeks.
  • May be idiopathic in up to 50% of cases or found in association with infection (bacterial, fungal, parasitic, viral), autoimmune disease (including production of auto-antibodies against the IgE receptor, triggering mast cell degranulation), or drug reaction. Whereas foods may be a relevant trigger for acute urticaria, the role of food allergies in chronic urticaria is controversial; a consistent, reproducible trigger is often not identified.
  • Because chronic urticaria may stem from an underlying systemic illness, it is important to perform a complete history and physical examination and pursue only basic laboratory testing and relevant diagnostic considerations. A cause is never found in a majority of cases.
  • The goal of therapy is to provide relief of symptoms.

Clinical presentation

Juicy pink to erythematous sometimes confluent into plaques, with edema and surrounding vasoconstriction (i.e., wheal).

Dermographic urticaria/ dermographism: results from frictional stress on the skin (such as scratching), eliciting rapid onset of urticarial lesions (1-5 minutes).

Differential diagnosis

It is imperative to determine whether the patient has urticaria alone or has a more systemic presentation with possible progression to angioedema or anaphylaxis. Careful review of symptoms of anaphylaxis, such as tongue, lip, or facial swelling, shortness of breath or wheezing, and diarrhea is necessary. Angioedema is characterized by deep tissue swelling (i.e., dermal or subcutaneous edema), pain more than itching, involvement of mucous membranes, and resolution that is slower than for urticaria (which typically resolves in < 24 hours); angioedema typically takes up to 72 hours to resolve.


  • Acute urticaria typically results from blood basophil or tissue mast cell degranulation triggered by IgE binding to antigens or through direct (non-IgE, non-immunologic) activation (by radiocontrast dye, NSAIDs, opiates, general anesthetics). This immune cell degranulation results in release of many immunologic mediators such as histamine (resulting in vasodilation and increased vascular permeability), leukotrienes, as well as cytokines and chemokines, resulting in local edema, erythema, as well as immune cell infiltrate.
  • Other mechanisms of urticaria, especially relevant to chronic urticaria, include:
    • Autoimmune: via IgE receptor crosslinking IgG
      • via anti-IgE IgG
      • via C5a
    • Physical urticaria: cold, pressure, cholinergic, vibratory, aquagenic, solar