Food Allergies: Diagnosis, Treatment, and Prevention

Dellyse M. Bright; Holly Leigh Stegall; David C. Slawson

DELLYSE M. BRIGHT, MD, HOLLY LEIGH STEGALL, MD, AND DAVID C. SLAWSON, MD

Am Fam Physician. 2023;108(2):159-165

Patient information: See related handout on food allergies.

This clinical content conforms to AAFP criteria for CME.

Author disclosure: No relevant financial relationships.

In the United States, approximately 2% to 3% of adults and 8% of children have a food allergy. Allergic reactions range from minor pruritus to life-threatening anaphylaxis. These allergies often lead to significant anxiety and costs for patients and caregivers. Common food allergies include peanuts, cow's milk, shellfish, tree nuts, egg, fish, soy, and wheat. Peanut allergy, the most common, is the leading cause of life-threatening anaphylaxis. Children with asthma, allergic rhinitis, atopic dermatitis, or an allergy to insect venom, medications, or latex are at an increased risk of developing food allergies. Diagnosis of food allergy starts with a detailed, allergy-focused history. Serum immunoglobulin E and skin prick testing provide reliable information regarding food allergy diagnoses. Primary treatment involves elimination of the offending food from the diet. Prevention strategies proven to decrease the risk of developing a food allergy include restricting exposure to cow's milk in the first three days of life and early sequential exposure to allergenic foods starting between four and six months of age. Exclusive breastfeeding for three to four months reduces the likelihood of developing eczema and asthma but does not reduce development of food allergies. Most children eventually outgrow allergies to cow's milk, egg, soy, and wheat. However, allergies to tree nuts, peanuts, and shellfish are more likely to be lifelong.

In the United States, approximately 2% to 3% of adults and 8% of children have a food allergy, and 40% of those children have multiple food allergies.^1,2 About 40% of food allergies in children are reported as severe, which can lead to significant costs and anxiety for parents and caregivers.² Common foods that produce allergies are peanuts, cow's milk, shellfish, tree nuts, egg, fish, soy, and wheat.^2,3 Peanut allergy, the most common (2%), is the leading cause of life-threatening anaphylaxis.^2,4 Children are likely to outgrow allergies to egg, cow's milk, wheat, and soy, whereas peanut, tree nut, fish, and shellfish allergies tend to persist throughout life.³ Peanut allergy resolves in approximately 1 in 5 children in the first four years of life.⁵

Clinical recommendation	Evidence rating	Comments
Serum immunoglobulin E or skin prick testing should be performed only when a detailed allergy-focused history indicates a high pretest probability of a food allergy.^3,9,12	C	Expert opinion and consensus guideline in the absence of high-quality clinical trials
Early introduction of peanuts, cow's milk, wheat, and cooked eggs between four and six months of age decreases the risk of developing food allergies.^16–18	A	Consistent results from randomized controlled trials and observational studies showing decreased development of food allergies
Early introduction of peanuts and cooked eggs at four to six months of age is safe and effective for reducing the risk of food allergy development in high-risk infants.^12,15,19,20	B	Randomized controlled trials that show decreased likelihood of developing food allergies at 36 months

Recommendation	Sponsoring organization
Do not perform screening panels for food allergies without previous consideration of medical history.	American Academy of Pediatrics
Do not perform food serum IgE testing without a history consistent with potential IgE-mediated food allergy.	American Academy of Allergy, Asthma and Immunology
Do not routinely avoid influenza vaccination in patients allergic to egg.	American Academy of Allergy, Asthma and Immunology

Risk Factors

Children with asthma, allergic rhinitis, atopic dermatitis, or an allergy to insect venom, medications, or latex are at an increased risk of developing food allergies^2,6 (Table 1²). Children with vitamin D insufficiency, a history of antibiotic use in the first two years of life, or a family history of atopy also have an increased risk of developing food allergies.^3,7,8 Other factors, including exercise, emotional stress, menses, alcohol consumption, and having a viral infection, can lower the reaction threshold and increase the risk of having an allergic reaction to food.^4,6

Symptoms

Food allergies are classified as immunoglobulin E (IgE)- and non–IgE-mediated. IgE-mediated allergies typically have a rapid onset, within seconds to minutes (e.g., pruritus, anaphylaxis). Non–IgE-mediated food allergies are characterized by delayed reactions, within hours to several days (e.g., food protein allergy–induced colitis).^6,9,10 The severity of the reaction is influenced by the amount of food ingested, form of the food (i.e., how it was prepared), and presence of other ingested foods.⁶ Symptoms of food allergies are listed in Table 2.^3,6,9,11

Organ system	Minor symptoms	Major symptoms/sequelae
Cardiovascular	Tachycardia	Hypotension, shock, syncope
Gastrointestinal	Blood or mucus in stools, colicky abdominal pain, constipation, diarrhea, fatigue, food aversion/refusal, nausea, oral pruritus, pallor, perianal redness, vomiting	Eosinophilic esophagitis, failure to thrive, growth delay, immune-mediated enterocolitis
Respiratory	Congestion, conjunctivitis, cough, nasal itching, rhinorrhea, sneezing, upper respiratory tract infection symptoms	Chest tightness, Heiner syndrome,* shortness of breath, wheezing
Skin	Acute urticaria, erythema, pruritus, worsening of atopic dermatitis	Angioedema (most commonly lips, face, and periorbital area)
Other	—	Anaphylaxis, systemic allergic reaction

Diagnosis

The rates of food allergies are overestimated because of self-reported food allergies that may be food intolerances.^1,12 Food intolerances are adverse reactions without an immunologic cause (e.g., lactose intolerance) and can be mistaken for food allergies.⁶ Differential diagnosis of food allergies is included in Table 3.^1,6

Diagnosis starts with a detailed history from the parent, caregiver, or patient. The amount and type of food that was eaten, form of the food (e.g., raw, extensively baked), time from ingestion to symptoms, presence of symptoms not associated with food, presence of risk factors that increase the likelihood of an allergic reaction (e.g., exercise), and number of reactions are essential components of an allergy-focused history.^6,9,10,12 Non–IgE-mediated food allergies should be considered in children without an adequate response to treatment for atopic dermatitis, gastroesophageal reflux disease, and chronic gastrointestinal symptoms, including chronic constipation.⁹

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Chu DK, Wood RA, French S, et al. Oral immunotherapy for peanut allergy (PACE): a systematic review and meta-analysis of efficacy and safety [published correction appears in Lancet. 2019; 393(10184): 1936]. Lancet. 2019;393(10187):2222-2232.

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Risk factor	Odds ratio
Latex allergy	7.9
Asthma	3.2
Urticaria	2.9
Insect venom allergy	2.5
Allergic rhinitis	2.3
Atopic dermatitis	1.9
Medication allergy	1.9

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