food allergy

Last reviewed 01/2018

Food allergy is an adverse immune response to a food. It can be classified into IgE-mediated and non-IgE-mediated reactions (1)

• many non-IgE reactions, which are poorly defined both clinically and scientifically, are believed to be T-cell-mediated. Some reactions involve a mixture of both IgE and non-IgE responses and are classified as mixed IgE and non-IgE allergic reactions
• food allergy may be confused with food intolerance, which is a non-immunological reaction that can be caused by enzyme deficiencies, pharmacological agents and naturally occurring substances (1)

Food allergy is defined as an adverse immunologic response to food, which occurs when oral tolerance fails to develop normally or 'breaks down' in genetically susceptible individuals

• food allergic reactions may be immediate or delayed
  • IgE mediated reactions are immediate - occurring within minutes to two hours of ingesting an allergen
    • cutaneous reactions - urticaria, erythematous rashes, angiooedema, eczema flare
    • gastrointestinal - vomiting, abdominal pain, diarrhoea, oral burning/itching
    • respiratory - wheeze, rhinitis, cough, stridor, voice change, dyspnoea
    • cardiovascular - hypotension (collapse, profound floppiness, loss of consciousness)
  • T-cell mediated are delayed and rarely life threatening
    • cutaneous - eczema
    • gastrointestinal - allergic eosinophilic oesophagitis, allergic eosinophilic gastroenteritis
    • respiratory - asthma
  • mixed reactions may occur
    • cutaneous - contact dermatitis, dermatitis herpetiformis
    • gastrointestinal - food protein-induced proctocolitis, food protein-induced enterocolitis and enteropathy, coeliac disease
    • respiratory - food-induced pulmonary hemosiderosis
      
      
• common foods causing allergic reactions in children are:
  • wheat
  • soybean
  • cow's milk
  • egg
  • peanuts
  • tree nuts
  • fish
  • shellfish
  • these foods account for about 85% of all allergic reactions to foods
    
    
• sensitisation is frequently 'occult' with reactions occurring on first known exposure
  • there is considerable homology due to the existence of cross-reacting proteins (panallergens) between various animal and plant proteins
    • some homologies are clinically important
      • e.g. 30-50% peanut allergics also react to tree nuts, most children with cow's milk intolerance will not be able to tolerate goat's milk
        
        
• diagnosis of food allergy depends on specific tests and elimination diets and food challenges
  
  
• most children (about 85%) lose their sensitivity to most allergenic foods (egg, milk, wheat, soya) within the first 3-5 years of life
  • food-specific IgE concentrations generally fall with tolerance. Even children with multiple, severe allergies usually achieve tolerance
  • however adults with food allergy can have long-lived sensitivity

Notes (1):

• if food allergy is suspected:

  • offer age-appropriate information that is relevant to the type of allergy (IgE-mediated, non-IgE-mediated or mixed). Include:
    • the type of allergy suspected
    • the risk of a severe allergic reaction
    • any impact on other healthcare issues such as vaccination
    • the diagnostic process, which may include:
      • an elimination diet followed by a possible planned rechallenge or initial food reintroduction procedure
      • skin prick tests and specific IgE antibody testing and their safety and limitations
      • referral to secondary or specialist care
  • support groups and how to contact them

Reference:

1. NICE (February 2011).Food allergy in children and young people Diagnosis and assessment of food allergy in children and young people in primary care and community settings
2. Pulse (March 26th 2005): 50-57.
3. Sicherer SH.Food allergy. The Lancet 2002; 360(9334):701-710