Dr Suzanne Dowling, Dr A Aston, Dr L Noimark
What is it??
Acute urticaria is the sudden appearance of wheals (a.k.a “nettle rash” or “hives”) and can be associated with tissue swelling (angioedema). The rash is raised, red, usually very itchy, and often has a pale centre but can also be papular. The raised areas can enlarge and coalesce. Acute urticaria tends to resolve within 24 hours, but can last longer (e.g. 48 hours). In chronic cases new hives may appear in the same or other areas, lasting longer.
Angioedema is the swelling of the lower layers of the skin. It can appear with urticaria overlying it or the skin can be normal in appearance. It can last longer than urticaria, often up to for 72 hours. Significant swelling can be painful.
The pathogenesis of both are not fully understood but it involves the release of inflammatory mediators, including histamine, from mast cells. 
This 6 year old girl presented to A&E early in the morning with an urticarial rash on her back and facial angioedema. The rash appeared overnight around 5am. She has no significant past medical history. Esther’s observations are all normal and she has no other symptoms.
Esther’s mother is worried it’s due to her eating some seeded bread with last night’s dinner. She hasn’t eaten seeds previously so the parents believe this must be the culprit. They have been reading about Epipens and wonder if Esther should have one.
What do we do next?
Pause for thought:
- 20% of people will have urticaria at some point in their lives and it is a common presentation to health professionals, particularly in children.
- While an allergic reaction always needs to be excluded, only 15-20% of those presenting with urticaria have a food allergy. The real incidence may be much lower , .
As with any assessment, start with ABC (to exclude anaphylaxis)
Vocal changes (hoarse voice)
Difficulty in swallowing
|Difficult or noisy breathing
Wheezing (Like an asthma attack)
|Feeling lightheaded or faint
Unresponsive/unconscious (due to a drop in blood pressure)
Phew! The Assessment shows no signs or symptoms of anaphylaxis.
- Take a photograph of the rash/swelling. To minimise confidentiality issues, use the family phone and to get the best image (if face-to-face) take it yourself. This may be needed for comparison later on or for review in clinic at a later stage.
- Exclude an allergic reaction. This is done through an allergy focused history and some basics around food allergy (e.g. EATERS ).
The EATERS mnemonic is help you interpret if the presenting complaint is likely to be an allergic reaction. It is based on the principle that all allergic reactions should have a relevant and timely exposure to an allergen. Reactions are more likely in certain environments. Symptoms and signs should fit the pattern and time frame of an acute allergic reaction and be reproducible.
Look at the table below to see what I mean:
By consumption of a food allergen.
|Has the child eaten or handled the food?
Or have they been kissed or touched by someone who is contaminated with that food?
More rarely, proximity to aerosolised allergens when food is fried can cause an exposure. Remember to check for exposure to other allergens such as animals, drugs and venom.
Is it a common food allergen?
|Milk, Egg, Nuts, Soya and Wheat are common allergens.Prawn and shellfish allergies are more common in older children. It is rare to have an isolated unusual food allergy.|
Between exposure and onset of symptoms.
|Most IgE mediated allergic reactions occur rapidly.Often within 15 minutes. They can be delayed by up to an hour, but this is less common. (E.g. when allergen is combined with a fatty substance that slows the release of the allergen, like chocolate)|
Where food allergic reactions are more common.
|Weaning from milk onto solids in infancy is a common time for food allergy presentation. Outside of this, most reactions occur in high risk environments such as restaurants/takeaways.|
symptoms’ Previous and future exposures to the same allergen.
|Most allergic reactions will occur at all exposures to the food. In infancy they may tolerate the food initially but react on the next exposure. If they have since tolerated that food, it is unlikely to be a food allergy.|
|Symptoms (typical) for an allergic reaction involving multiple organ systems.||Skin: hives, swelling, redness, itch.
Gut: vomiting, abdominal pain, diarrhoea.
Respiratory tract: rhinorrhoea, cough, wheeze, hoarseness, stridor.
Neurological: change in behaviour, sleepiness, feeling of doom.
Cardiovascular: shock and collapse.
Check for risk factors such as the presence of other allergic comorbidities.
|Eczema, asthma, food allergy and allergic rhinitis.Immediate family history for atopic disease.|
Let’s apply an EATERS history to Esther
Exposure -> Esther ate seeds for the first time last night.
Allergen -> Esther ate bread containing poppy seeds.
Timing -> Her symptoms started 10 hours after eating the new food.
This doesn’t fit with an immediate allergic reaction.
Environment -> Esther ate at home.
So, her food is less likely to be contaminated with unknown allergens.
Reproducible -> Esther had not eaten poppy seeds prior to this event.
Symptoms -> Esther has skin symptoms, but no other organs are involved.
Her rash started on her back not around the site of exposure.
Risk Factors -> She has no personal or family history of atopy.
Whilst seeds are a potential allergen, the timing of urticaria development doesn’t fit with an allergic reaction.
Generally, specific IgE mediated food allergies do not occur ten hours after exposure to the allergen.
Esther has no risk factors for allergy, such as a personal or family history of atopy.
You can feel confident this doesn’t fit with food allergy.
But what did cause her rash? Part two takes us through the aetiology of acute urticaria and angiodema
- Methods report on the development of the 2013 revision and update of the EAACI /GA2LEN /EDF /WAO guideline for the definition, classification, diagnosis, and management of urticaria
- Allergy UK: Urticaria, hives and other skin allergy
- BSACI guideline for the management of chronic urticaria and angioedema
- BMJ Best Practise Urticaria and angio-oedema [Updated 2018]
- Fifteen-minute consultation: The EATERS method for the diagnosis of food allergies Archives of Disease in Childhood – Education and Practice
Written and reviewed August 2020
Dr Suzanne Dowling Paediatric ST6, Royal London Hospital General Paediatrics & Allergy registrar Reviewed by Dr A Aston Paediatric Allergy Consultant, RLH and Dr L Noimark Paediatric Allergy Consultant, RLH