Emergent Care / Stabilization:
Emergency first-line treatment of an anaphylactic reaction to a food allergen is epinephrine injected intramuscularly (IM) immediately, then every 5-15 minutes as needed. Dosing is as follows:

• Adults: 0.01 mg up to 0.5 mg
• Children: 0.01 mL/kg (up to 0.3 mg)

If a premeasured autoinjector is not used, 1:1000 epinephrine (1 mg / 1 mL) should be drawn up in a 1-mL syringe and administered IM. Intranasal epinephrine spray is a viable alternative to an autoinjector for anaphylaxis in some patients.

Hypotensive patients will need intravenous fluids. Severely hypotensive patients may need vasopressors. It is important to keep in mind the patient's medication history as beta blockers may inhibit a patient's response to epinephrine. After a patient's condition is stabilized with epinephrine and fluids, they may need intravenous or oral diphenhydramine, and steroids.

Diagnosis Overview:
Food allergies most commonly occur in the first 1-2 years of life. Some will resolve over time (months to years), while others will persist throughout an individual's life. Adult-onset food allergies are less common than those that begin during childhood, but they are still significant. Generally, the prevalence of food allergies may be as high as 10% of people in Western countries. The prevalence of self-reported food allergies in the United States is higher than that of physician-reported food allergies (per a 2010 US Food and Drug Administration [FDA] food safety survey, 13% and 6.5%, respectively). Common food triggers include peanuts, tree nuts, milk, shellfish, fruit, egg, soy, and wheat. Among adult-onset food allergies, seafood allergies are the most common. Up to 60% of shellfish allergies are diagnosed during adulthood. True milk allergies (ie, cow's milk allergy) are uncommon in adults, but cow's milk allergy is the most common food allergy in children.

Hypersensitivities classically develop through primary sensitization, with either gastrointestinal (GI) or cutaneous exposure resulting in the development of an immune response to an allergen. Some of these allergies may occur through secondary sensitization, or allergen cross-reactivity. For example, someone who develops a hypersensitivity to dust mite or cockroach proteins may later develop shellfish allergies.

There are 5 main presentations of food hypersensitivity disorders in adults:

1. Immunoglobulin E (IgE)-mediated anaphylaxis (most common)
2. Food-dependent, exercise-induced anaphylaxis
3. Oral allergy syndrome
4. Delayed anaphylaxis to mammalian meats (see alpha-gal syndrome)
5. Food protein-induced enterocolitis syndrome

Anaphylaxis is the most severe type of allergic reaction. Anaphylaxis is characterized by rapid onset and multiple organ system involvement. Symptoms generally begin within minutes of exposure. Symptoms include urticaria, pruritus, shortness of breath or difficulty breathing, vomiting, diarrhea, tachycardia, and hypotension. Immediate recognition of anaphylaxis and administration of epinephrine is crucial. Delay in treatment with epinephrine and a history of asthma increase an individual's mortality risk during an anaphylactic reaction.