Food Allergies
When the immune system overreacts to a particular food
Quick Facts
- Type: Immune (allergic) condition
- Common triggers: Peanuts, tree nuts, milk, egg, shellfish
- Most severe form: Anaphylaxis (medical emergency)
- Emergency treatment: Epinephrine auto-injector
Overview
A food allergy is an immune system reaction that happens soon after eating a certain food. The body mistakenly treats a harmless food protein as a threat and releases chemicals such as histamine, producing symptoms that can affect the skin, gut, airways, and circulation. Even a tiny amount of the food can trigger a reaction in some people.
Food allergies are different from food intolerances, which involve digestion rather than the immune system and are uncomfortable but not life-threatening. A true food allergy can range from mild itching and hives to anaphylaxis, a severe, rapid reaction that is a medical emergency.
Symptoms
Symptoms usually appear within minutes to a couple of hours of eating the trigger food.
- Itching, hives, or eczema flare on the skin
- Tingling or itching in the mouth, swelling of the lips, tongue, or throat
- Stomach cramps, nausea, vomiting, or diarrhea
- Coughing, wheezing, or shortness of breath
- Runny or stuffy nose, sneezing, and watery eyes
Anaphylaxis is an emergency. Signs include trouble breathing, throat tightness, swelling of the tongue or throat, a sudden drop in blood pressure with dizziness or fainting, a rapid pulse, and a feeling of impending doom. If these occur, use an epinephrine auto-injector if available and call emergency services right away.
Causes
Food allergies occur when the immune system produces antibodies (usually IgE) against a specific food protein. On re-exposure, those antibodies trigger the release of histamine and other chemicals that cause symptoms. A small number of foods account for most reactions:
- In children: Milk, egg, peanut, tree nuts, soy, and wheat.
- In adults: Peanut, tree nuts, fish, and shellfish.
- Other triggers: Sesame and certain seeds and fruits.
Some reactions are delayed or non-IgE in nature, affecting mainly the gut. A related condition, oral allergy syndrome, causes mild mouth itching from raw fruits and vegetables in people allergic to certain pollens.
Risk Factors
- A personal or family history of allergies, asthma, eczema, or hay fever
- Having one food allergy (raises the chance of others)
- Young age (food allergies are more common in children)
- A history of severe allergic reactions
- Asthma, which increases the risk of a severe reaction
Diagnosis
Diagnosis combines a careful history of what was eaten and what happened with allergy testing.
- Medical history: Details of the food, timing, and symptoms are central to diagnosis.
- Skin prick test: A small amount of the suspected food is placed on the skin to see if a hive forms.
- Blood tests: Measure allergy antibodies (IgE) to specific foods.
- Oral food challenge: Eating gradually increasing amounts of the food under medical supervision, considered the most definitive test.
- Elimination diet: Removing suspect foods and reintroducing them to identify triggers.
Treatment
The foundation of management is strictly avoiding the trigger food and being prepared to treat reactions.
- Avoidance: Reading labels carefully, asking about ingredients when eating out, and preventing cross-contact in food preparation.
- Epinephrine auto-injector: People at risk of anaphylaxis should carry epinephrine and know how to use it; it is the first-line treatment for severe reactions.
- Antihistamines: May relieve mild symptoms such as itching or hives, but do not treat anaphylaxis.
- Emergency plan: A written action plan helps the person and caregivers respond quickly.
- Oral immunotherapy: For some allergies, supervised programs that introduce tiny, increasing amounts of the food may reduce reaction severity.
After using epinephrine, always seek emergency care, because symptoms can return.
Prevention
- Avoid known trigger foods and check ingredient labels every time
- Carry prescribed epinephrine at all times if you are at risk of anaphylaxis
- Wear a medical alert bracelet noting the allergy
- Inform schools, restaurants, and caregivers about the allergy
- Prevent cross-contact by using clean utensils and surfaces
- For infants at risk, follow a clinician's guidance on early introduction of allergenic foods such as peanut
When to See a Doctor
Call emergency services immediately for signs of anaphylaxis: trouble breathing, throat tightness or swelling, widespread hives with dizziness or fainting, or a rapid weak pulse. Use an epinephrine auto-injector right away if one is available.
See a clinician or allergist to:
- Confirm a suspected food allergy with testing
- Get a prescription for epinephrine and an action plan
- Review reactions that are becoming more frequent or severe
- Discuss whether immunotherapy or supervised food challenges are appropriate
Frequently Asked Questions
What is the difference between a food allergy and a food intolerance?
A food allergy involves the immune system and can cause reactions ranging from hives to life-threatening anaphylaxis. A food intolerance, such as lactose intolerance, involves digestion, causes symptoms like bloating or diarrhea, and is uncomfortable but not dangerous to the airway or circulation.
What should I do if someone is having a severe allergic reaction to food?
If there are signs of anaphylaxis, such as trouble breathing, throat swelling, or fainting, use an epinephrine auto-injector immediately if one is available and call emergency services. Have the person lie down with legs raised, and seek emergency care even if symptoms improve, because they can return.
Which foods most commonly cause allergies?
The most common triggers are peanuts, tree nuts, milk, egg, soy, wheat, fish, shellfish, and sesame. In children, milk, egg, and peanut are frequent, while peanut, tree nuts, fish, and shellfish are the most common adult triggers.
Can children outgrow food allergies?
Many children outgrow allergies to milk, egg, soy, and wheat, while allergies to peanuts, tree nuts, fish, and shellfish are more often lifelong. An allergist can monitor whether an allergy has resolved using testing and supervised food challenges.
Do antihistamines treat a serious food allergy reaction?
Antihistamines may ease mild symptoms such as itching or hives, but they do not treat anaphylaxis. The only first-line treatment for a severe reaction is epinephrine, followed by emergency medical care.
References
- Mayo Clinic. Food allergy — Symptoms and causes.
- National Institute of Allergy and Infectious Diseases (NIAID). Food Allergy.
- American Academy of Allergy, Asthma & Immunology (AAAAI). Food Allergy.
- MedlinePlus, U.S. National Library of Medicine. Food allergy.