Massachusetts General Hospital

Food Allergies

What is food allergy?

A food allergy is an abnormal response of the body to a certain food. It is important to know that this is different from a food intolerance, which does not affect the immune system, although some of the same signs may be present.

What causes food allergy?

Before having a food allergy reaction, a sensitive person must be exposed to the food at least once before. It is the second time the person eats the food that the allergic symptoms happen. At that time, when IgE antibodies react with the food, histamines are released, which can cause hives, asthma, itching in the mouth, trouble breathing, stomach pains, vomiting, or diarrhea.

What is the difference between food allergy and food intolerance?

Food allergy causes an immune system response, causing symptoms that range from uncomfortable to life-threatening. Food intolerance does not affect the immune system, although some symptoms may be the same as in food allergy.

What foods most often cause food allergy?

Approximately 90 percent of all food allergies are caused by eight foods, including the following:

• Milk

• Eggs

• Wheat

• Soy

• Tree nuts

• Fish

• Shellfish

• Peanuts

Eggs, milk, and peanuts are the most common causes of food allergies in children, with wheat, soy, and tree nuts also included. Peanuts, nuts, fish, and shellfish commonly cause the most severe reactions. Nearly 5 percent of children under the age of 5 years have food allergies. From 1997 to 2007, the prevalence of reported food allergy increased 18 percent among children under age 18 years. Although most children "outgrow" their allergies, allergy to peanuts, tree nuts, and shellfish may be lifelong.

What are the symptoms of food allergy?

Allergic symptoms may begin within minutes to an hour after ingesting the food. The following are the most common symptoms of a food allergy. However, each individual may experience symptoms differently. Symptoms may include:

• Vomiting

• Diarrhea

• Cramps

• Hives

• Swelling

• Eczema

• Itching or swelling of the lips, tongue, or mouth

• Itching or tightness in the throat

• Difficulty breathing

• Wheezing

• Lowered blood pressure

According to the National Institute of Allergy and Infectious Disease, it does not take much of the food to cause a severe reaction in highly allergic people. In fact, as little as 1/44,000 of a peanut kernel can cause an allergic reaction for severely allergic individuals.

The symptoms of a food allergy may resemble other medical conditions or problems. Always consult your doctor for a diagnosis.

Treatment for a food allergy in adults

Specific treatment for a food allergy will be determined by your doctor based on:

• Your age, overall health, and medical history

• Extent of the disease

• Your tolerance for specific medications, procedures, or therapies

• Expectations for the course of the disease

• Your opinion or preference

At this time, no medication is available to prevent food allergy. The goal of treatment is to avoid the food that causes the symptoms.

People with food allergy must be prepared to treat any accidental ingestion of the foods that cause the allergic reaction. Discuss this further with your doctor.

There are medications available to treat some symptoms of food allergy after the food has been eaten. These medications may relieve rhinitis symptoms, gastrointestinal symptoms, or asthma symptoms. Discuss this further with your doctor.

Although research is ongoing, currently, there is no allergy injection approved for the treatment of food allergies. Strictly avoiding the allergy-causing food is the only way to prevent a reaction.

Treatment of food allergies in children

After being examined by a doctor and determining foods to which your child is allergic, it is very important to avoid these foods and other similar foods in that food group. If you are breastfeeding your child, it is important to avoid foods in your diet to which your child is allergic. Small amounts of the food allergen may go to your child through the breast milk and cause a reaction.

It is also important to give vitamins and minerals to your child if he or she is unable to eat certain foods. Discuss this further with your child's doctor.

For children who have a food allergy, your child's doctor may prescribe an emergency kit that contains epinephrine, which helps stop the symptoms of severe reactions. Discuss this further with your child's doctor.

Some children, under the direction of your doctor, may be given certain foods again after three to six months to determine if the child has outgrown the allergy. Many allergies may be short-term in children and the food may be tolerated after the age of 3 or 4.

What is anaphylaxis?

Anaphylaxis, also called anaphylactic shock, is a severe and sometimes life-threatening reaction to an allergen (the items that you are allergic to are called allergens). It is a medical emergency, in most cases. The reaction to the allergen can occur seconds to as long as an hour after the exposure. It is necessary to have come in contact with the allergen at a previous time for sensitization to occur.

What causes anaphylaxis?

Anaphylaxis is caused by exposure to an allergen. The type of allergen may be different for every person. Some of the most common causes include the following:

• Medications, such as penicillin

• Foods

• Dyes used for medical procedures

• Allergy injections

• Insect stings

• Latex

What are the symptoms of anaphylaxis?

The following are the most common symptoms of anaphylaxis. However, each individual may experience symptoms differently. Symptoms may include:

• Tightness or swelling of the throat

• Wheezing or difficulty breathing

• Uneasy sensation or agitation

• Generalized hives

• Severe itching of the skin

• Nausea and vomiting

• Stomach pain

• Heart failure

• Irregular heartbeats

• Lowered blood pressure

The symptoms of anaphylaxis may resemble other medical conditions or problems. Always consult your doctor for a diagnosis.

Treatment for anaphylaxis

Anaphylaxis is a medical emergency. Immediate medical attention is necessary. Your doctor will probably treat the symptoms with an injection of epinephrine, which will help stop the severe effects caused by the allergen. If you do have an anaphylactic reaction to an allergen, your doctor may instruct you on the use of an emergency kit that contains epinephrine to have near you in case of future episodes. Discuss this with your doctor.