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 
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)
- Skin: (most common): pruritus, urticaria,atopic dermatitis exanthem, angioedema
- Respiratory: rhinitis (often with sneezing), nasal congestion, dyspnea, wheezing, laryngeal edema
- Gastrointestinal tract: nausea, vomiting, abdominal pain, diarrhea, oral allergy syndrome (oral pruritus, tingling numbness, and swelling of the lips, tongue, palate, and throat)
- Cardiovascular: hypotension, tachycardia, dysrhythmias
- CNS: headache
Non-IgE or mixed reactions are typically limited to the skin and the gastrointestinal tract.
Respiratory manifestations can be fatal.
Subtypes and variants
Food protein-induced allergic proctocolitis of infancy (FPIAP)
- Definition: a type of delayed inflammatory non-IgE-mediated food allergy typically seen in young infants that affects the distal colon
- Epidemiology: primarily affects young infants (typically manifests at 2–8 weeks of age)
- Hypersensitivity reaction to certain foods, most commonly cow's milk, followed by soy protein, rice, and eggs 
- Associated with a personal and family history of atopy 
- Insidious progression of symptoms over several months
- Rectal bleeding
- Increased stool frequency
- Streaks of mucus in the stool
- Abdominal pain
- Affected infants typically appear otherwise healthy.
- Insidious progression of symptoms over several months
Diagnostics: mainly a clinical diagnosis based on patient history and clinical features
- Patient history: evaluation of infant's and mother's diet
- Laboratory testing: may reveal eosinophilia, mild iron deficiency anemia, and/or increased fecal calprotectin
- Differential diagnosis
Removal of offending foods from the infant's diet
- Elimination of all dairy and soy products from the mother's diet
- Continue breastfeeding
- Formula-fed infants: switching to a hydrolyzed formula (e.g., hydrolyzed casein)
- Breastfed infants
- The offending foods should be carefully reintroduced to assess tolerance after one year of age.
- Removal of offending foods from the infant's diet
- Complications: chronic colitis and/or persistent food allergy (rare)
- Gross rectal bleeding usually improves within 3–4 days of removing the offending food. 
- FPIAP usually resolves spontaneously by one year of age. 
- 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.
- 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)
- Psychosocial factors (e.g., exposure to stress)
- Otherwise healthy infant with appropriate weight gain
- Paroxysmal episodes of loud and high pitched crying that often occur at the same time each day (usually in the late afternoon or evening)
- Hypertonia (e.g., clenched fists, stretched legs) 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
- Soothing techniques
- Trial of various feeding techniques
If the child appears unwell, further examination is necessary to rule out serious conditions (e.g., intussusception).
The differential diagnoses listed here are not exhaustive.
- Avoid allergens; and, in case of emergency, treat anaphylactic reactions (see “Treatment of anaphylaxis”)
- Oral immunotherapy is a novel approach, that is still being studied and not widely available
- The majority of children with milk and egg allergies will outgrow them by 5 years of age.
- A lot of children with food allergies will develop asthma and allergic rhinitis.
- Adult-onset food allergies usually remain for life.