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Food allergies

Last updated: March 26, 2021

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Food allergies are hypersensitivity reactions to allergens contained in food. They are the most common cause of anaphylaxis-related emergency admissions. Young children are commonly affected, usually beginning in the first two years of life. IgE-mediated reactions are the most common type and have an onset within minutes after ingestion. Clinical features include urticaria, angioedema, wheezing, rhinitis, and abdominal pain. Food intolerance on the other hand does not result in an immune reaction and usually only causes abdominal discomfort. A thorough patient history followed by a skin prick test or radioallergosorbent test (RAST) usually confirm the suspected allergen. Management includes desensitization, avoidance of triggers, treatment of symptoms, and, in the event of anaphylaxis, administration of epinephrine.

  • Most common cause of anaphylaxis-related emergency admissions
  • 5% of adults, 8% of children [1]

Epidemiological data refers to the US, unless otherwise specified.

  • Hypersensitivity reaction against select ingredients in food
  • The most common food allergens are cow's milk, eggs, nuts, peanuts , seafood (e.g., shellfish, fish), soy, wheat, fruits (e.g., kiwi)
  • Commonly IgE-mediated: Type I hypersensitivity reaction (immediate onset; within minutes to 2 hours of ingestion)
  • Mixed IgE/non-IgE-mediated and non-IgE-mediated reactions are also possible (delayed onset; hours to days after ingestion)

Non-IgE or mixed reactions are typically limited to the skin and the gastrointestinal tract.

Respiratory manifestations can be fatal!

  • Patient history: determine type of food, time and amount of ingestion, and the type of reaction
  • Suspected IgE-mediated reaction
    • IgE skin prick test
    • RAST (radioallergosorbent test)
      • An immunoassay that detects specific compounds using antibodies coupled to radioactive tags.
      • Previously used to detect allergen-specific IgE but is no longer widely used.
      • IgE serum levels are measured in response to predetermined food allergens.
    • Total IgE-antibody serum test
    • N-methylhistamine (urine)
  • If above tests are inconclusive or suspected food is not a common allergen
    • Elimination diet: The suspected allergens are eliminated from the patient diet, while being observed for an improvement in symptoms without the need for medication.
    • Oral food challenge: the effect of potential allergens on the mucous membranes is tested (the patient is given different foods that contain potential allergens to chew but not swallow in increasing doses over a fixed period of time). May be implemented after a positive elimination diet.

Infantile colic

  • Etiology
    • Unknown
    • Gastrointestinal (e.g., overfeeding or underfeeding, aerophagia, cow's milk intolerance), biologic (e.g., increased serotonin levels, tobacco exposure, dysfunctional motor regulation related to immaturity), and psychosocial (e.g., exposure to stress) factors are suspected
  • Clinical features
    • Healthy and thriving infant
    • Paroxysmal episodes of loud and high pitched crying
    • Hypertonia (e.g., clenched fists) during episodes
    • Infant is not easily consoled
  • Diagnostics: crying that lasts ≥ 3 hours per day, ≥ 3 days per week, for ≥ 3 weeks in an otherwise healthy infant <3 months
  • Treatment
    • Reassurance
    • Trial of various feeding and soothing techniques

Intolerance reactions

If blood appears in stools, further examination is necessary, as it is likely that a more serious condition (e.g., intussusception) is involved!

The differential diagnoses listed here are not exhaustive.


  1. Sicherer SH, Sampson HA. Food allergy: epidemiology, pathogenesis, diagnosis, and treatment. J Allergy Clin Immunol. 2014; 133 (2): p.291-307. doi: 10.1016/j.jaci.2013.11.020 . | Open in Read by QxMD
  2. Chad Z . Allergies in children. Paediatr Child Health. 2001; 6 (8): p.555-566.