Skip to content

Food Allergy

BASICS

  • Immune-mediated hypersensitivity reaction reproducibly triggered by specific foods
  • IgE-mediated food allergy is the focus here
  • Systems involved: gastrointestinal, hematologic/immune, pulmonary, skin, cardiovascular
  • Synonyms: IgE-mediated food reactions, food hypersensitivity, anaphylaxis

EPIDEMIOLOGY

  • Affects all ages; traditionally infants and children but increasing prevalence in adults
  • Male predominance in children; female predominance in adults
  • Disproportionate impact on underserved and minority populations
  • Prevalence by challenge testing: ~3%
  • Self-reported prevalence >10% (1 in 10 adults, 1 in 12 children)
  • Common childhood allergens: cow’s milk (2%), egg (0.6-0.8%), peanut (1.2-2%), tree nuts (~1%)
  • Adult allergens: shellfish (2.9%), milk (1.9%), peanut (1.8%), tree nuts (1.2%), fish (0.9%)
  • Most milk and egg allergies resolve in childhood; ~20% peanut allergy resolves by school age

ETIOLOGY AND PATHOPHYSIOLOGY

  • Failure of immunologic tolerance to food proteins leading to IgE-mediated hypersensitivity
  • Common allergens (90%): milk, egg white, wheat, soy, peanut, tree nuts, fish, shellfish
  • Rare causes: food dyes, additives
  • Genetic factors include certain HLA alleles associated with peanut allergy
  • Screening siblings of affected patients not currently recommended

RISK FACTORS

  • Male sex in children, female in adults
  • Atopic predisposition, especially eczema
  • Family history of food allergy

GENERAL PREVENTION

  • Early introduction of peanut and egg around 6 months of age (not before 4 months)
  • Avoid delayed introduction of allergenic foods
  • Maintain epinephrine availability for those at risk of anaphylaxis

COMMONLY ASSOCIATED CONDITIONS

  • Food protein-induced enterocolitis syndrome (FPIES), eosinophilic esophagitis
  • Atopic dermatitis, asthma, allergic rhinitis

DIAGNOSIS

History

  • Symptoms within minutes after food ingestion
  • GI: nausea, vomiting, diarrhea, abdominal pain
  • Skin: urticaria, angioedema, flushing
  • Respiratory: rhinitis, asthma, bronchospasm, stridor, cough
  • Systemic: anaphylaxis, ocular injection
  • Inquire about cofactors (exercise, sleep deprivation, NSAIDs, alcohol, illness)
  • Differentiate from food intolerance

Physical Exam

  • Vital signs, growth parameters
  • Signs of allergic disease (skin, pulmonary)
  • Additional exam based on presentation

Differential Diagnosis

  • Nonimmune food intolerance (lactose intolerance)
  • Toxic exposures (scombroid poisoning)
  • GI disorders (IBS, celiac disease, IBD)
  • Chronic urticaria
  • Psychiatric causes
  • Other immune-mediated food reactions (oral allergy syndrome, α-gal syndrome, food-dependent exercise anaphylaxis, FPIES)

Diagnostic Tests

  • Allergy skin prick testing: high sensitivity, low specificity
  • Serum food-specific IgE: targeted testing based on history
  • Component-resolved diagnostics (CRD) for specific allergen proteins
  • Double-blind, placebo-controlled oral food challenge is gold standard
  • Avoid widespread or non-targeted testing
  • Unproven tests: IgG testing, leukocytotoxic assays, hair analysis

TREATMENT

General Measures

  • Strict avoidance of offending foods
  • Carry epinephrine autoinjectors for anaphylaxis risk
  • Immunotherapy for selected food allergies (e.g., oral peanut immunotherapy)
  • Avoid subcutaneous immunotherapy with food extracts

Medications

  • Epinephrine for systemic anaphylaxis (repeat dose in ~20% cases)
  • Antihistamines for mild symptoms
  • Oral peanut immunotherapy (Palforzia) approved for ages 4-17 years to reduce risk of anaphylaxis

Complementary & Alternative Medicine

  • Insufficient evidence for herbal medicines, probiotics, or prebiotics

ONGOING CARE

  • Follow-up with periodic skin or serum IgE as indicated
  • Dietary counseling to maintain nutrition while avoiding allergens

PATIENT EDUCATION

  • Resources: Food Allergy Research & Education (FARE), AAAAI, ACAAI websites
  • Breastfeeding recommended first 6 months, especially with family atopy
  • Avoid delaying solids beyond 6 months

PROGNOSIS

  • Many children outgrow milk, egg, wheat allergies; ~20% peanut allergies resolve by age 5
  • Adult allergies to milk, fish, shellfish, nuts often persistent

COMPLICATIONS

  • Anaphylaxis
  • Angioedema, asthma, environmental allergies
  • Reduced quality of life, anxiety, depression

REFERENCES

  1. Warren CM, Jiang J, Gupta RS. Epidemiology and burden of food allergy. Curr Allergy Asthma Rep. 2020;20(2):6.
  2. Coulson E, Rifas-Shiman SL, Sordillo J, et al. Racial, ethnic, and socioeconomic differences in adolescent food allergy. J Allergy Clin Immunol Pract. 2020;8(1):336-338.e3.
  3. Gupta RS, Warren CM, Smith BM, et al. Prevalence and severity of food allergies among US adults. JAMA Netw Open. 2019;2(1):e185630.
  4. Bird JA, ed. Food Allergy, an Issue of Immunology and Allergy Clinics of North America. Elsevier Health Sciences; 2017.

CODES

  • ICD10: T78.1XXA Other adverse food reactions, initial encounter
  • ICD10: T78.00XA Anaphylactic reaction due to unspecified food, initial encounter
  • ICD10: L27.2 Dermatitis due to ingested food

CLINICAL PEARLS

  • Up to 20% of children with peanut allergy may outgrow sensitivity; most others outgrow milk, egg, wheat allergies by adulthood.
  • Oral itching with fresh fruit ingestion suggests oral allergy syndrome.
  • Maternal dietary restrictions during pregnancy and lactation do not prevent atopy or food allergy in infants.
  • Breastfeeding for 6 months is recommended, especially if family history of atopy or allergy.
  • Delaying introduction of solids beyond 6 months does not prevent allergy development.
  • Introduce peanut and egg around 6 months (not before 4 months), consider skin testing in high-risk infants.