Acute urticaria

hives · weals · wheals · nettle rash · dermographism

Itchy weals that move, each one gone within a day - common, usually self-limiting, and dangerous only when it is the skin half of anaphylaxis.

DISCHARGEBand D

Red flags

Any airway, breathing or circulatory involvement is anaphylaxis, not urticaria - voice change, stridor, throat or tongue swelling, difficulty swallowing, wheeze or breathlessness; or pallor and clamminess, tachycardia, faintness, collapse or reduced consciousness. Hypotension is a late sign and is particularly late in children - do not wait for it. Persistent vomiting or abdominal pain after a food or sting, or a sense of impending doom, belongs in the same bracket. Give intramuscular adrenaline and manage per the Resuscitation Council UK algorithm; do not wait to see whether the rash settles
A reaction already treated with adrenaline needs observation for a biphasic recurrence, not discharge on an antihistamine - CKS notes these are hard to predict
Angio-oedema with the weals - deep swelling of the lips, tongue, face or throat - needs the angio-oedema entry and an airway assessment, not an antihistamine and discharge
Individual lesions lasting more than 24 hours, painful or burning rather than itchy, non-blanching or palpable, or leaving bruising or pigment as they fade - CKS says to consider urticarial vasculitis, particularly with fever, malaise or arthralgia, and that needs investigation
A systemically unwell patient - urticaria itself does not make people unwell, so look for the illness that is causing it
Urticaria beginning within an hour of a food, drug or sting, in a patient who is now well - still counts as a possible allergic reaction and needs advice and follow-up rather than plain reassurance

Recognise

On light skin

Raised pink or red weals of very variable size, often with pale centres and a surrounding flare, intensely itchy, and each individual lesion resolving within hours without a mark.

On brown and black skin

The flare - the surrounding redness that makes a weal obvious in pale skin - is frequently invisible, and the weal itself may be skin-coloured, paler than the surrounding skin, or only slightly darker, so the eruption can be missed entirely on inspection. That colour description is clinical observation rather than a cited finding; what is cited is CKS’s own wording that the central swelling may be red or white, which is the point that matters. This is a condition you diagnose with your hands and with the history. Run a hand across the skin: the weal is raised, and the change in surface contour is palpable when it is not visible. CKS's own description helps here, because it notes the central swelling may be red or white rather than assuming redness. Ask about itch, ask whether individual spots come and go within a day, and mark one with a pen to test that directly. Post-inflammatory hyperpigmentation may follow and can be mistaken for the rash persisting.

In any skin tone

Each individual weal lasts less than 24 hours and leaves no mark - CKS puts the fleeting nature, with skin returning to normal, at 1 to 24 hours. Mark one with a pen and re-examine: this single test does most of the diagnostic work
Itch, or sometimes a burning sensation, is close to invariable - an eruption that does not itch is probably not urticaria
Weals are palpably raised, of very variable size, and migratory - new ones appear as old ones fade
Acute is under 6 weeks; chronic is 6 weeks or longer on a nearly daily basis (CKS)
Dermographism - weals appearing in the line of a scratch - is a physical variant and is a useful bedside confirmation
Ask about triggers: a new drug, an infection, an insect sting, a food eaten within the hour, exercise, heat or cold

Distribution

Anywhere, and characteristically migratory - individual weals come and go over hours while the eruption as a whole persists. Dermographism appears in lines where the skin has been scratched or rubbed.

Photographs

Acute urticaria on brown skin. The weal is an annular ring with a slightly raised border and a paler centre - the erythema that makes this o — Acute urticaria on brown skin. The weal is an **annular ring with a slightly raised border and a paler centre** - the erythema that makes this obvious on white skin is almost absent, so the lesion is found by **surface contour and by the patient's history of itch**, not by colour. The photograph is poorly lit and has a strong yellow cast: that is the camera, not the patient.
Fitzpatrick IV-VI (Fitzpatrick type estimated from the photograph, not stated by the source) · irvin calicut · Wikimedia Commons - Idiopathic urticaria (2).jpg · CC BY-SA 3.0

Acute urticaria on white skin, same disease: coalescing annular and polycyclic weals with pale centres on a child's torso, described by the — Acute urticaria on white skin, same disease: **coalescing annular and polycyclic weals with pale centres** on a child's torso, described by the photographer as acute viral urticaria. Compare it with the image above - this is the appearance most clinicians carry in their heads, and it is the reason the first photograph gets missed.
Fitzpatrick I-III (Fitzpatrick type estimated from the photograph, not stated by the source) · Gzzz · Wikimedia Commons - Urticaria child.jpg · CC BY-SA 4.0

Broad confluent weals across the trunk and arms of a 9-year-old, raised enough to throw their own shadows - the swelling, not the redness, i — Broad confluent weals across the trunk and arms of a 9-year-old, **raised enough to throw their own shadows** - the swelling, not the redness, is the diagnostic feature. The photographer records that this appeared suddenly and had resolved completely within 8 hours, which is the **individual weals last under 24 hours** rule in one picture.
Fitzpatrick I-III (Fitzpatrick type estimated from the photograph, not stated by the source) · Wikimedia Commons user מ.י.ש.הו 0 (released CC0; attributed here as house style) · Wikimedia Commons - Urticaria12.2024.jpg · CC0 1.0

Provenance for every photograph in this library: image licences. How much of the corpus still has no darker-skin photograph: skin tone coverage.

Mimics

Urticarial vasculitis — The distinction that matters. Ordinary weals are fleeting, itchy and leave nothing behind; vasculitic lesions outlast 24 hours, burn or hurt, and leave bruising or pigment
Angio-oedema - allergic, ACE-inhibitor and hereditary — The deep counterpart of the same process - and the presence or absence of weals is what separates a histamine-mediated from a bradykinin-mediated mechanism
Drug eruptions - morbilliform and fixed — A morbilliform drug rash is fixed in place for days, whereas urticarial lesions migrate within hours
Erythema multiforme major — Target lesions are fixed, have a concentric structure and persist for days; urticarial lesions are transient and have no true target
IgA vasculitis (Henoch-Schonlein purpura) — Early IgA vasculitis in a child can look urticarial before it becomes purpuric - palpable purpura on the buttocks and legs that does not fade is the discriminator

What to do in the ED

Assess airway, breathing and circulation first. Urticaria is a skin diagnosis only once anaphylaxis has been excluded, and the rash is the least important part of an anaphylactic reaction
Mark a weal with a pen and record the time. Re-examining it later is the cleanest way to demonstrate the under-24-hour behaviour, and it is the evidence the next clinician needs
Examine by palpation as well as inspection, particularly in brown and black skin, where the weal may be felt rather than seen
Take a focused trigger history over the preceding hours to days: drugs including over-the-counter and complementary ones, foods, stings, infections, exercise and physical stimuli
A non-sedating antihistamine daily for up to 6 weeks, with a short course of an oral corticosteroid of up to 7 days added for severe symptoms. A one-week course of prednisolone does not need tapering. The international EAACI/GA2LEN/EuroGuiDerm guideline below is the independent reference for the stepped approach; CKS is the primary-care one
In a child the antihistamine choice is age-dependent, and CKS says so explicitly - licensed ages differ. Cetirizine is licensed from 2 years (2.5 mg twice daily at 2 to 5 years, 5 mg twice daily at 6 to 11), and is not licensed below 2, where the BNFC gives an unlicensed dose. Fexofenadine is licensed only from 12 years. Take the dose from the BNFC against age and weight rather than prescribing as for an adult
Where itch is disturbing sleep, a sedating antihistamine such as chlorphenamine may be added at night
Where a specific trigger is identified, say so explicitly, document it, and give written avoidance advice - an identified trigger is the whole value of the attendance
Where the urticaria began within an hour of a food, drug or sting, observe for a period before discharge, and make sure the patient will not be alone for the next few hours. CKS is clear that most allergic skin changes do not progress to anaphylaxis - but the ones that do, do so early
Do not investigate acute urticaria routinely - investigations are not usually required to make the diagnosis

Disposition

DISCHARGE

Treat and discharge once anaphylaxis and angio-oedema are excluded. Acute urticaria is usually self-limiting. Refer to allergy or immunology where there is a clear and avoidable trigger with a systemic reaction, and to dermatology or immunology where it becomes chronic.

Safety-netting

Take the antihistamine regularly rather than only when the spots appear - it works better that way. Individual spots should fade within a day, though new ones may keep appearing for a while. Come back immediately, by ambulance, if your lips, tongue or throat swell, if your voice changes, if you become wheezy or short of breath, or if you feel faint - that is a different and serious reaction. Also return if the spots last longer than a day each, become painful rather than itchy, or leave bruises behind. See your GP if it is still happening after six weeks.

Sources

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