see also:

• anaphylaxis
• angioedema
• histamine physiology, receptors and antihistamines
• RCH guideline - urticaria
• eosinophilia
• allergy and hypersensitivity reactions
• acute rashes in adults
• erythema multiforme

• urticaria or hives is a common pruritic wheal-type generalised rash which has many causes, the most common being viral infections (50%), food allergic reactions (25%), drug reactions (10%), idiopathic (20%), inhalants (2%), bites (1%), contact (0.2%)
• ~9% of people develop an acute urticaria
• ~2% of people develop a chronic urticaria (lasts >6 weeks) - mainly young children and the elderly
• 60% of cases are also associated with angioedema which typically is painful rather than itchy as it is deeper layers of skin or mucosa, and lasts 3 days. Angioedema associated with urticaria is less worrisome than that occurring without urticaria.
• the far majority of cases are NOT IgE antibody related and are NOT associated with anaphylaxis and are generally NOT helped by corticosteroids nor by adrenaline / epinephrine¹⁾
• the lesions can be confused with erythema multiforme although these lesions are not pruritic
• hive wheals individually only last up to 24hrs, lesions lasting longer than this suggest a vasculitic aetiology or delayed pressure urticaria rather than usual urticarial mast cell release aetiology
• an attack of urticaria usually lasts a week or two, but may last longer
• urticaria caused by food presents within 2hrs of ingestion with 90% presenting within minutes, thus ingestions more than 2 hr prior to onset are extremely unlikely to be due to that food.
• ~94% of cases of food allergy result in a skin reaction such as urticaria
• delayed onset serum sickness reactions such as those following Rx with cefaclor also cause urticarial like lesions, but in association with joint effusions

• remove trigger but avoid advising diet restrictions unless strongly suspect a specific NEW food - avoidance of foods increases risk of allergy if allergy does not already exist to that food in those with allergies.
• daily non-sedating antihistamines (H1) for at least 3 days and up to 3 wks
• consider adding promethazine dose at night
• if poor response try changing non-sedating antihistamine and if still troublesome, consider adding ltra and referral to immunologist

• 60% idiopathic eg. stress, viral, autoimmune (anti FCeR1 IgG - assoc. with Hashimoto's thyroiditis)
• 5% vasculitic eg. Rare CAPS syndrome
• remainder are
  • physical eg. Exercise, delayed pressure, cold, solar, etc
  • drug-induced eg. non-steroidal anti-inflammatory drugs (NSAIDs)
  • contact eg. Latex, food, IgE
  • angioedema without wheals eg. Idiopathic, hereditary angioedema (HAE), ACE inhibitors

• non-sedating antihistamines (H1) for 2weeks, consider increasing dose
• consider adding ltra
• consider adding corticosteroids for 3-7 days
• investigations are usually fruitless (1 in 2000 will detect treatable condition such as thyroiditis) but many do them anyway, such as FBE, ESR, CRP, LFTs, TFT but DON'T bother with total IgE levels are this is useless
• consider referral to immunologist
• consider skin biopsy if ? Vasculitis
• stool for helminths
• msu to excl. urinary tract infections (UTIs) / cystitis
• consider hep B, C serology
• consider ANA, Rh factor, cryoglobulins
• consider using cyclosporin A, dapsone, omalizumab

• strongly suspected specific trigger
• severe attacks
• lasting >6wks
• lesions last > 24hrs hence need to exclude vasculitic causes
• FH recurrent or chronic urticaria

• a self-limiting urticaria usually due viral infections, or, less commonly, to contact with, or ingestion of an allergen (food or medications), or following an insect sting
• weals are well defined raised lesions with a smooth surface, may be red or white, surrounded by a red or white flare
• weals range in size from a few millimetres to many centimetres in diameter
• they are assymetric and randomly distributed on the body and may affect any site
• individual weals last no more than 24 hours and do not leave any marks behind.
• the most common triggers are:
  • shellfish
  • nuts
  • eggs in infants
  • wheat
  • soy
  • medications eg. antibiotics, aspirin (acetylsalicylic acid), non-steroidal anti-inflammatory drugs (NSAIDs)
  • viruses
  • Streptococci
• onset is often within minutes
• most will settle within 10-14 days and are best managed with avoidance of trigger and hot baths and symptomatic relief with antihistamines
• it may be part of more serious allergic reactions such as anaphylaxis in which case early Rx with im adrenaline, corticosteroids and antihistamines, and hospital observation is indicated

• these are acute, recurrent, localised to trigger region, SHORT DURATION (last <1hr except for delayed pressure urticaria which lasts for hours to days) wheal-type reactions that occur in response to local physical stimuli such as:
  • 5% of people develop raised linear,wheal-like dermographism within 30min following firm stroking of the skin
  • acetylcholine released during sweating in cholinergic urticaria
    • smaller wheal lesion “spots” especially on upper trunk and arms which tend to resolve after 60-90 minutes
    • rarely affects the palms, soles or the armpits
    • those who are more severely affected may experience systemic symptoms such as headaches, salivation, palpitations, fainting, shortness of breath, wheezing, abdominal cramps and diarrhoea, and rarely may develop anaphylaxis
  • cold air or water in cold urticaria
    • common form causes rapid onset urticaria to face, neck and hands on exposure to cold
    • rare hereditary form causes generalised urticaria 9-18 hours after cold exposure
  • local heat in heat urticaria
  • a contact factor in contact urticaria
  • water of any type or temperature in aquagenic urticaria
  • sun exposure in solar urticaria
    • urticaria follows UV exposure within minutes and generally resolves over a few hours, rarely lasting more than 24 hrs.
  • firm pressure in delayed pressure urticaria
    • such as from tight clothing causes gradual onset wheal-like lesions after 6hrs following trigger and lasts 8hrs-3 days

• strongyloidiasis may cause urticarial lesions around the waist and buttocks

• see also https://www.dermnetnz.org/topics/shiitake-flagellate-dermatitis/
• an intensely pruritic 1mm micropapular erythematous rash which looks like whip marks due to Koebnerization due to patient scratching
• rare outside of Asia
• occurs 12hrs to 5 days after eating shiitake mushrooms (when eaten raw or only lightly cooked) in ~2% of people and most resolve within 3 weeks
• appears to be a reaction to lentinan, a thermolabile polysaccharide
• similar rash can occur with:
  • use of bleomycin, peplomycin or docetaxel
  • Adult-onset Still disease
  • dermatomyositis

• urticaria lasting > 6 weeks, often lasting 1-20years
• rarely due to allergy

• insect bite or sting
  • single weal which may last weeks, usually has a central blister/vesicle, and tends to turn brownish for a few months
• miliaria ruba / prickly heat rash
  • similar to cholinergic urticaria but generally lasts 1-2 days and resolves when hot humid conditions are avided
  • itchy, red, 2–4 mm, non-follicular papules and papulovesicles, often with background erythema
  • in adults, often affects the upper trunk, scalp, neck and flexures, particularly in areas of friction with clothing.
  • in children, involves the trunk and the skin folds of the neck, axilla or groin.
• urticarial dermatitis
  • usually in the elderly and the chronic pruritus can severely affect quality of life
  • symmetric persistent red itchy plaques may have a smooth surface (urticaria-like) usually to trunk, upper arms and upper thighs
  • can be an early sign of bullous pemphigoid
• contact dermatitis
  • local dermatitis, which, unlike contact urticaria, takes days to weeks to resolve and a patch test may reveal an allergen
• Grover's disease (transient acantholytic dermatosis) common in middle age, mainly truncal and itchy
• erythema multiforme
  • an acute eruption of target-shaped lesions on the hands, feet, knees and elbows.
  • unlike urticarial weals, individual lesions persist for ten days to 3 weeks and there may be mucosal lesions
  • may be recurrent, usually due to herpes simplex virus infection
• urticarial multiforme
  • a morphological subtype of urticaria, a benign cutaneous hypersensitivity reaction predominantly mediated by histamine seen in paediatric patients that is characterized by the acute and transient onset of blanchable, annular, polycyclic, erythematous wheals with dusky, ecchymotic centers in association with acral oedema (hands, feet, face)
• serum sickness
• urticarial vasculitis
• urticarial drug eruptions
  • rash starts within 14 days of a new medication (except in drug hypersensitivity syndrome, when they arise within eight weeks of starting a new medication)
  • symmetrical and tends to be most severe on the trunk
  • peeling may occur as it resolves and dark marks may persist for days to weeks
• urticaria pigmentosa
  • mainly seen in infants, and is a form of cutaneous mastocytosis in which there are brown macules and papules.
• autoimmune blistering diseases
  • these may initially present with symmetric urticarial lesions esp of trunk and skin flexures, several days or weeks before blisters appear
  • eg. bullous pemphigoid (mainly elderly), pemphigoid gestationis, linear IgA bullous dermatosis, epidermolysis bullosa acquisita
• pruritic urticarial papules and plaques of pregnancy (PUPPP)
  • an eruption occurring during the last few weeks of pregnancy, usually in a first pregnancy
  • usually start in the stretch marks (striae gravidarum)
  • resolve in puerperium
• annular erythema
  • asymptomatic enlarging rings
• other rare rashes