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Food allergy

Medically reviewed by Drugs.com. Last updated on May 27, 2025.

What is a food allergy?

Harvard Health Publishing

A food allergy is a reaction by the body's immune system to something in a food, usually a protein; the body mistakenly acts like it is a germ or some other invader, and does its best to defend itself.

While any food could possibly cause an allergy, certain foods are much more likely to do so. In children, the foods that most commonly cause allergic reactions are:

Most allergic reactions occur within 30 minutes of consuming the problem food. Often, the reaction occurs within five to 10 minutes, but it can occur as long as four to six hours after ingestion.

Food allergy is different from food intolerance. In food intolerance, there is a physical reaction to a food, but that reaction isn't allergic. Lactose intolerance is a common example. People who suffer from this have trouble digesting one of the sugars in milk, and can have stomachaches or diarrhea when they drink milk or eat dairy products.

While the symptoms of food intolerance can be uncomfortable, this condition is not dangerous. There are also other conditions such as celiac disease that can cause reactions to foods (people with celiac disease have trouble with anything containing gluten) that are not allergic.

Another form of allergy is called oral allergy syndrome. People who have this get itching of the lips, mouth, and throat (and sometimes swollen lips) after eating certain fruits or vegetables. This is rarely dangerous.

Food allergies are becoming more common, especially among children. While the exact cause of food allergy is unknown, it does tend to run in families.

Symptoms of food allergy

It's not always easy to know when someone has a food allergy, because there are many different symptoms. They include:

In severe cases, a dangerous reaction called anaphylaxis can happen. This whole-body allergic reaction combines many of the symptoms mentioned above, and can lead to death if not treated immediately.

Diagnosing food allergy

Many times, the diagnosis of food allergy can be made by the history. For example, if a child has hives or swelling of the face after eating something with peanuts, they are likely allergic to peanuts. But because symptoms can be so varied and food exposures so numerous, the diagnosis is sometimes harder to make. A detailed diary of food intake and symptoms and information about food allergies in the family can be helpful. But your doctor may need to do testing to be sure.

There are two commonly used tests:

Skin tests. The allergy skin-prick test involves pricking the skin with a solution of the suspected food. A positive test will produce a small hivelike reaction.

The downside of this test is that it is uncomfortable – and for children with eczema or other skin conditions, the results may be difficult to interpret. And in children with severe allergies, even the small amount of the food injected into the skin can cause significant reactions.

Another problem with skin tests is that in order for them to be truly reliable, the patient can't take any antihistamines for about two weeks before the test. For children who suffer with bad hay fever or other allergies, two weeks without antihistamines may be challenging.

Blood tests. Laboratory tests can measure the amount of food-specific IgE in the blood. IgE antibodies are made by the body in response to allergens. Once you have developed these IgE antibodies, they are constantly circulating in your blood. Therefore, this blood test can be done at any time. The greater the amount of IgE, the higher the probability the person has an allergy to that particular food.

These tests have the advantage of being less uncomfortable (one needle stick for the blood test instead of a bunch of needle sticks for the skin test) and can be done without stopping antihistamines. The downside of these tests (besides the expense) is that they can have both false positive and false negative results.

A supervised "food challenge" is sometimes recommended to evaluate suspected food allergy. This should only be performed by an allergy specialist with experience treating food allergies and who has the necessary medications and equipment to handle sever reactions.

Preventing food allergy

Previously, experts believed that avoiding foods that commonly cause allergies early in life could help prevent allergies. Research now shows that the opposite is true. Exposing infants to foods such as peanuts (being careful to avoid any choking risk) may prevent allergies. This is particularly true for infants who have severe eczema, or who have a family history of food allergies. Talk to your doctor about the best plan for your child.

For older children who have developed allergies, the best way to avoid an allergic reaction is to avoid the food or foods that cause a reaction. Here are some steps you can take.

Newer preventive options include oral immunotherapy (OIT) and a medication called omalizumab (Xolair).

OIT is a type of desensitization in which a person consumes a tiny amount of the food (or a small portion of the food) and then gradually increases the amount. OIT can reduce the frequency and severity of food allergies. Currently, OIT is only approved for peanut allergies, although some health care providers offer OIT for other foods.

Omalizumab is an antibody treatment that blocks IgE and is FDA-approved for adults and children who are at least 1 year of age to prevent anaphylaxis due to inadvertent exposure to one or more foods.

There are significant limitations to both of these newer approaches including cost, uncertain effectiveness, and the continued need to avoid the problematic foods.

Expected duration of food allergy

While most children outgrow food allergies, some carry them into adulthood. Teenagers need to be aware of food allergies they had as children and not assume they have outgrown them. In particular, allergies to peanuts, tree nuts, fish, and shellfish usually are not outgrown.

Treating food allergy

For minor allergic reactions, over-the-counter or prescription antihistamines or nasal sprays can be used to relieve the symptoms. Talk to your doctor about the best medication for your child.

Severe reactions require prompt medical attention. Epinephrine via an injection device can be lifesaving. If epinephrine is used, the child still needs medical attention, as symptoms can return once the medication wears off. All those caring for the child should be instructed to either call 911 or take the child directly to an emergency room (never take the child yourself if there is any trouble breathing or the child appears ill — always call 911).

There are new treatments for allergy that are undergoing research; hopefully, we will have more ways to prevent and treat them in the future.

When to call a professional

If you or your child develops allergic symptoms after eating, call a health care professional immediately. If breathing difficulties occur, call 911.

Prognosis

The symptoms of food allergy can range from mild to life-threatening. If a food or ingredient is easy to avoid, the allergy may interfere very little with daily life. Some foods and ingredients, however, are widespread, and avoiding them will involve careful monitoring. Some food allergies disappear as a child ages.

Additional info

The Food Allergy & Anaphylaxis Network
http://www.foodallergy.org/

National Institute of Allergy and Infectious Diseases (NIAID)
http://www.niaid.nih.gov/

American Academy of Allergy, Asthma & Immunology (AAAAI)
http://www.aaaai.org/


Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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