Urticaria
Also called hives, wheals
Mast-cell-driven transient wheals: raised, smooth, intensely itchy, and gone from any one site within 24 hours even as new crops appear. The time course is the diagnosis.
How it looks
Multiple transient, smooth, oedematous erythematous wheals of varying size scattered over the trunk and limbs, individual lesions resolving within hours.
Rose is the lesion, grey the pattern the lesions make, green where on the body it lives.
Across skin tones
Wheals may show little visible colour change in deeply pigmented skin, look for the raised oedematous contour and rely on palpation.
Don't miss
Wheals plus lip or tongue swelling, wheeze, or hypotension is anaphylaxis. Individual fixed lesions lasting over 48 hours that bruise on resolution suggest urticarial vasculitis, biopsy that.
Forms & variants
Acute urticaria
Under six weeks of wheals; infections, drugs, and foods lead the causes, and often none is found or needed.
Chronic spontaneous urticaria
Wheals most days for more than six weeks; usually mast-cell autoimmunity rather than allergy, so testing follows the history, not a panel.
Dermatographism
Wheals rise exactly where the skin is stroked, the commonest physical urticaria; write on the forearm to demonstrate it.
Cholinergic urticaria
Pinpoint wheals in a red flare whenever core temperature rises: exercise, hot showers, strong emotion.
Cold urticaria
Wheals appear on rewarming after cold exposure; an ice-cube test confirms it, and open-water swimming becomes genuinely dangerous.
Heat, pressure, and aquagenic urticaria
Rarer physical forms: wheals from local heat contact, deep delayed wheals under sustained pressure (straps, seats, tools), or wheals wherever water touches, at any temperature.
Symptoms & course
- Pronounced itch
- Individual lesions migrate and vanish within 24 hours
Diagnostic approach
- None for a first uncomplicated episode
- Draw a circle around a wheal: still there unchanged at 24–48 hours argues against simple urticaria
Differential, and how to separate them
- Morbilliform drug eruption
Favours it: Fixed maculopapules lasting days, recent new drug
Against it: Urticarial wheals move; morbilliform lesions stay put
Management principles
- Non-sedating H1 antihistamines, up-titrated, are the mainstay
- Identify triggers; epinephrine only for anaphylaxis, not isolated hives
Clinical pearl: Dermatographism, writing on the skin with a wheal, is the bedside demonstration of the mechanism.
Keep going
Try the case: Welts that will not sit stillCompare with Morbilliform drug eruptionBack to the Atlas