Acute Urticaria — ED Treatment

Key Points

• First decide whether the patient has anaphylaxis, not merely hives.
• IM epinephrine is first-line for anaphylaxis but is not required for isolated uncomplicated urticaria.
• Second-generation H1 antihistamines are preferred for acute urticaria.
• First-generation antihistamines cause more sedation and anticholinergic effects.
• Routine systemic corticosteroids are not necessary for most uncomplicated acute urticaria.
• Fixed painful lesions lasting more than 24 hours suggest an alternative diagnosis such as urticarial vasculitis.
• ACE-inhibitor and hereditary bradykinin-mediated angioedema may occur without hives and respond poorly to antihistamines.
• Broad laboratory testing is unnecessary for a typical short-lived episode.

Algorithm

1. Assess airway, breathing, circulation, blood pressure, GI symptoms, and speed of progression.
2. If anaphylaxis criteria are met, give IM epinephrine immediately and manage as anaphylaxis.
3. If isolated wheals or mild histaminergic angioedema are present, give a second-generation H1 antihistamine.
4. Review new medications, foods, infections, stings, NSAIDs, and physical triggers.
5. Reassess for evolving airway or systemic symptoms.
6. Discharge improving uncomplicated urticaria with antihistamine plan and return precautions.
7. Refer for recurrent, persistent, atypical, or trigger-specific disease.

Clinical Synopsis & Reasoning

Urticaria consists of pruritic, raised, blanching wheals that change shape and location and usually resolve within 24 hours at any one site. Angioedema involves deeper dermal and submucosal swelling and may accompany hives. Acute urticaria lasts less than six weeks and is commonly idiopathic or associated with viral infection, medication exposure, food, insect sting, or another transient trigger.

The most important assessment is whether the patient has anaphylaxis. Hives plus respiratory compromise, hypotension, significant gastrointestinal symptoms after a likely allergen, or rapidly evolving multi-system involvement should be treated as anaphylaxis with intramuscular epinephrine. Isolated skin findings without airway, breathing, or circulatory involvement are not anaphylaxis and do not require epinephrine solely because the rash is dramatic.

Next separate histamine-mediated urticaria from other eruptions. Individual lesions that remain fixed longer than 24 hours, are painful rather than itchy, leave bruising or hyperpigmentation, or occur with systemic inflammatory findings suggest urticarial vasculitis or another diagnosis. Nonurticarial angioedema without hives, particularly from ACE inhibitors or hereditary bradykinin disorders, is less responsive to antihistamines and epinephrine unless anaphylaxis is also present.

Broad laboratory testing is not useful for uncomplicated acute urticaria. The history should focus on timing relative to foods, medications, infection, stings, latex, exercise, temperature, and NSAIDs. A trigger identified only by temporal association should not automatically become a permanent allergy label without appropriate follow-up.

Treatment Strategy & Disposition

For isolated acute urticaria, use a second-generation H1 antihistamine such as cetirizine, loratadine, or fexofenadine. These are preferred to routine first-generation agents because they cause less sedation and anticholinergic toxicity. Cetirizine has a relatively rapid onset and is commonly used in emergency care. For substantial symptoms, higher-than-standard antihistamine dosing may be used according to urticaria guidance and clinician judgment.

Do not use systemic corticosteroids routinely for simple acute urticaria. They do not treat anaphylaxis and can cause hyperglycemia, mood effects, insomnia, and other adverse events. A short course is sometimes considered for unusually severe persistent symptoms after anaphylaxis has been excluded, but evidence of meaningful benefit is limited and antihistamines remain the core therapy.

If anaphylaxis is present, give IM epinephrine promptly in the mid-anterolateral thigh and follow the anaphylaxis pathway. Antihistamines are adjuncts for itching and hives and must never delay epinephrine. Airway angioedema, stridor, voice change, tongue swelling, hypoxemia, or hypotension requires monitored emergency management even if skin symptoms are prominent.

Discharge uncomplicated urticaria when symptoms are improving and no systemic or airway features are present. Avoid the suspected trigger if one is compelling, but do not create broad unnecessary dietary restrictions. Recurrent episodes, symptoms approaching six weeks, atypical lesions, or suspected specific allergy warrant outpatient evaluation.

Epidemiology / Risk Factors

• Acute urticaria is common and often has no single identifiable cause.
• Viral infections are frequent triggers, particularly in children and young adults.
• Food and drug allergy are important when symptom timing is tightly linked to exposure.
• Most isolated acute episodes resolve within days.
• Progression beyond six weeks changes the classification to chronic urticaria and changes the diagnostic and treatment strategy.

Investigations

When to Suspect Anaphylaxis

Pharmacology

Prognosis / Complications

• Most acute urticaria resolves completely without sequelae.
• Recurrence can occur if the trigger is re-encountered or if the episode is evolving into chronic spontaneous urticaria.
• Anaphylaxis risk depends on the underlying trigger and systemic involvement rather than the surface area of hives.
• Atypical lesions require reassessment because vasculitis and other inflammatory disorders have different prognoses.
• Avoiding unnecessary permanent allergy labels improves future treatment options.

Patient Education / Counseling

• Use a non-sedating antihistamine as directed and understand that hives may migrate before fully resolving.
• Call emergency services for trouble breathing, throat tightness, fainting, severe wheezing, or rapidly worsening multi-system symptoms.
• Avoid a strongly suspected trigger until reviewed, but do not eliminate broad food groups without evidence.
• Photograph recurrent lesions because the rash may disappear before follow-up.
• Seek reassessment if individual lesions persist in the same location longer than 24 hours, bruise, or become painful.
• If episodes continue for six weeks or longer, arrange evaluation for chronic urticaria.

Notes

The term allergic reaction is too broad to guide emergency therapy. A patient with isolated hives needs antihistamine treatment and observation for progression. A patient with hives plus respiratory or circulatory compromise needs epinephrine immediately. The distinction should be made at the bedside before adding secondary medications.

Another important distinction is duration. Acute urticaria and chronic spontaneous urticaria share a mast-cell phenotype but differ in cause, workup, and long-term therapy. Extensive testing during a single short-lived episode is usually more confusing than helpful.

References

1. AAAAI/ACAAI Anaphylaxis 2023 Practice Parameter Update — Link
2. International Urticaria Guideline 2026 — Link