The first step is to identify possible food allergy and differentiate the possible causes:

IgE-mediated	Non-IgE-mediated
Skin
• pruritus
• erythema
• urticaria
• angioedemaGastrointestinal system
• nausea
• colicky abdominal pain
• vomiting
• diarrhoeaRespiratory system
• upper respiratory tract symptoms - nasal itching,sneezing, rhinorrhoea or congestion (with or without conjunctivitis)
• lower respiratory tract symptoms - cough, chest tightness, wheezing or shortness of breathSymptoms of anaphylaxis	Skin
• pruritus
• erythema
• atopic eczemaGastrointestinal system
• gastro-oesophageal reflux disease
• loose or frequent stools
• blood and/or mucus in stools
• abdominal pain
• infantile colic
• food refusal or aversion
• constipation
• perianal redness
• pallor and tiredness
• faltering growth plus one or more gastrointestinal symptoms above (with or without significant atopic eczema)

If the history is suggestive of an IgE-mediated allergy

offer a skin prick test or blood tests for specific IgE antibodies to the suspected foods and likely co-allergens

If the history is suggestive of an non-IgE-mediated allergy

eliminate the suspected allergen for 2-6 weeks, then reintroduce. NICE advise to 'consult a dietitian with appropriate competencies about nutritional adequacies, timings and follow-up'

Allergy Testing

Skin Patch Test

The skin patch test involves applying a small amount of suspect allergen (in this case nickel) onto a patch, which is then placed on the patient's skin. After 48 hours, the patch is removed and any reaction is assessed. This test is considered safe and effective for diagnosing allergic contact dermatitis.

Skin Prick Test

This type of test is primarily used to identify immediate hypersensitivity reactions, such as those seen in food or respiratory allergies. It involves introducing small amounts of allergens into the skin via tiny pricks or punctures and observing for an immediate wheal-and-flare reaction.