Health Information Library

Overview

Food allergy is an immune system reaction that happens soon after eating a certain food. Even a tiny amount of the allergy-causing food can trigger symptoms such as hives, swollen airways and digestive problems. In some people, a food allergy can cause severe symptoms or even a life-threatening reaction known as anaphylaxis.

Food allergy affects an estimated 8% of children under age 5 and up to 4% of adults. While there's no cure, some children outgrow their food allergies as they get older.

It's easy to confuse a food allergy with a much more common reaction known as food intolerance. While bothersome, food intolerance is a less serious condition that does not involve the immune system.

Symptoms

For some people, an allergic reaction to a particular food may be uncomfortable but not severe. For other people, a food allergy reaction can be frightening and even life-threatening. Food allergy symptoms usually develop within a few minutes to two hours after eating the offending food. Rarely, symptoms may be delayed for several hours.

The most common food allergy symptoms include:

• Tingling or itching in the mouth.
• Hives, itching or eczema.
• Swelling of the lips, face, tongue, and throat or other parts of the body.
• Belly pain, diarrhea, nausea or vomiting.
• Wheezing, nasal congestion or trouble breathing.
• Dizziness, lightheadedness or fainting.

Anaphylaxis

In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening symptoms, including:

• Constriction and tightening of the airways.
• A swollen throat or the sensation of a lump in your throat that makes it hard to breathe.
• Shock with a severe drop in blood pressure.
• Rapid pulse.
• Dizziness, lightheadedness or loss of consciousness.

Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can be fatal.

When to see a doctor

See a healthcare professional or allergist if you have food allergy symptoms shortly after eating. If possible, see a care professional when the allergic reaction is occurring. This can help make a diagnosis.

Seek emergency treatment if you develop any symptoms of anaphylaxis, such as:

• Constriction of airways that makes it difficult to breathe.
• Shock with a severe drop in blood pressure.
• Rapid pulse.
• Dizziness or lightheadedness.

Causes

When you have a food allergy, your immune system mistakenly identifies a specific food or a substance in food as something harmful. In response, your immune system triggers cells to make an antibody known as immunoglobulin E (IgE) to recognize the allergy-causing food or food substance, called an allergen.

The next time you eat even the smallest amount of that food, IgE antibodies sense it. They then signal your immune system to release a chemical called histamine, as well as other chemicals, into your bloodstream. These chemicals cause allergy symptoms.

Most food allergies are triggered by certain proteins in:

• Crustacean shellfish, such as shrimp, lobster and crab.
• Peanuts.
• Tree nuts, such as walnuts and pecans.
• Fish.
• Chicken eggs.
• Cow's milk.
• Wheat.
• Soy.

Pollen-food allergy syndrome

Also known as oral allergy syndrome, pollen-food allergy syndrome affects many people who have hay fever. In this condition, certain fresh fruits and vegetables or nuts and spices can trigger an allergic reaction that causes the mouth to tingle or itch. In serious cases, the reaction results in swelling of the throat or even anaphylaxis.

Proteins in certain fruits, vegetables, nuts and spices cause the reaction because they're similar to allergy-causing proteins found in certain pollens. This is an example of cross-reactivity.

Symptoms are typically triggered by eating these foods when they're fresh and uncooked. However, when these foods are cooked, symptoms may be less severe.

The following table shows the specific fruits, vegetables, nuts and spices that can cause pollen-food allergy syndrome in people who are allergic to different pollens.

Exercise-induced food allergy

Eating certain foods may cause some people to feel itchy and lightheaded soon after starting to exercise. Serious cases may even involve hives or anaphylaxis. Not eating for a couple of hours before exercising and avoiding certain foods may help prevent this problem.

Food intolerance and other reactions

A food intolerance or a reaction to another substance you ate may cause the same symptoms as a food allergy does — such as nausea, vomiting, cramping and diarrhea.

Depending on the type of food intolerance you have, you may be able to eat small amounts of problem foods without a reaction. By contrast, if you have a true food allergy, even a tiny amount of the food may trigger an allergic reaction.

One of the tricky aspects of diagnosing food intolerance is that some people are sensitive not to the food itself but to a substance or ingredient used in the preparation of the food.

Common conditions that can cause symptoms mistaken for a food allergy include:

• Absence of an enzyme needed to fully digest a food. You may not have enough of some of the enzymes needed to digest certain foods. Insufficient amounts of the enzyme lactase, for example, reduce your ability to digest lactose, the main sugar in milk products. Lactose intolerance can cause bloating, cramping, diarrhea and excess gas.
• Food poisoning. Sometimes food poisoning can mimic an allergic reaction. Bacteria in spoiled tuna and other fish also can make a toxin that triggers harmful reactions.
• Sensitivity to food additives. Some people have digestive reactions and other symptoms after eating certain food additives. For example, sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in people with sensitivity to food additives.
• Histamine toxicity. Certain fish, such as tuna or mackerel, that are not refrigerated properly and that contain high amounts of bacteria also may contain high levels of histamine that trigger symptoms similar to those of food allergy. Rather than an allergic reaction, this is known as histamine toxicity or scombroid poisoning.

• Celiac disease. While celiac disease is sometimes referred to as a gluten allergy, it does not result in anaphylaxis. Like a food allergy, celiac disease does involve an immune system response, but it's a unique reaction that's more complex than a simple food allergy.

  This ongoing digestive condition is triggered by eating gluten, a protein found in bread, pasta, cookies and many other foods containing wheat, barley or rye.

  If you have celiac disease and eat foods containing gluten, an immune reaction happens that causes damage to the surface of your small intestine. This leads to an inability to absorb certain nutrients.

Risk factors

Food allergy risk factors include:

• Family history. You're at increased risk of food allergies if asthma, eczema, hives or allergies such as hay fever are common in your family.
• Other allergies. If you're already allergic to one food, you may be at increased risk of becoming allergic to another. Similarly, if you have other types of allergic reactions, such as hay fever or eczema, your risk of having a food allergy is greater.

• Age. Food allergies are more common in children, especially toddlers and infants. As children grow older, their digestive systems mature and their bodies are less likely to react to food components that trigger allergies.

  Fortunately, children typically outgrow allergies to milk, soy, wheat and eggs. Severe allergies and allergies to nuts and shellfish are more likely to be lifelong.

• Asthma. Asthma and food allergy commonly occur together. When they do, both food allergy and asthma symptoms are more likely to be severe.

Factors that may increase your risk of developing an anaphylactic reaction include:

• Having a history of asthma.
• Being a teenager or younger.
• Delaying use of epinephrine to treat your food allergy symptoms.
• Not having hives or other skin symptoms.

Complications

Complications of food allergy can include:

• Anaphylaxis. This is a life-threatening allergic reaction.
• Atopic dermatitis, known as eczema. Food allergy may cause a skin reaction, such as eczema.

Prevention

Early exposure

Early introduction of peanut products has been associated with a lower risk of peanut allergy. In an important study, high-risk infants — such as those with atopic dermatitis or egg allergy or both — were selected to either ingest or avoid peanut products from 4 to 6 months of age until 5 years of age.

Researchers found that high-risk children who regularly consumed peanut protein, such as peanut butter or peanut-flavored snacks, were around 80% less likely to develop a peanut allergy.

Before introducing allergenic foods, talk with your child's healthcare team about the best time to offer them.

Taking precautions

Once a food allergy has already developed, the best way to prevent an allergic reaction is to know and avoid foods that cause signs and symptoms. For some people, this is a mere inconvenience, but others find it very difficult. Also, some foods — when used as ingredients in certain dishes — may be well hidden. This is especially true in restaurants and in other social settings.

If you know you have a food allergy, follow these steps:

• Know what you're eating and drinking. Be sure to read food labels carefully.
• If you have already had a severe reaction, wear a medical alert bracelet or necklace that lets others know that you have a food allergy in case you have a reaction and you're unable to communicate.
• Talk with your healthcare team about prescribing emergency epinephrine. You may need to carry an epinephrine autoinjector (Adrenaclick, EpiPen) if you're at risk of a severe allergic reaction.

• Be careful at restaurants. Be certain your server or chef is aware that you absolutely can't eat the food you're allergic to, and you need to be completely certain that the meal you order doesn't contain it. Also, make sure food isn't prepared on surfaces or in pans that contained any of the food you're allergic to.

  Don't be reluctant to make your needs known. Restaurant staff members are usually more than happy to help when they clearly understand your request.

• Plan meals and snacks before leaving home. If necessary, take a cooler packed with allergen-free foods when you travel or go to an event. If you or your child can't have the cake or dessert at a party, bring an approved special treat so no one feels left out of the celebration.

If your child has a food allergy, take these precautions to ensure your child's safety:

• Notify key people that your child has a food allergy. Talk with childcare providers, school personnel, parents of your child's friends and other adults who regularly interact with your child. Emphasize that an allergic reaction can be life-threatening and requires immediate action. Make sure that your child also knows to ask for help right away if your child reacts to food.
• Explain food allergy symptoms. Teach the adults who spend time with your child how to recognize signs and symptoms of an allergic reaction.
• Write an action plan. Your plan should describe how to care for your child when your child has an allergic reaction to food. Provide a copy of the plan to your child's school nurse and others who care for and supervise your child.
• Have your child wear a medical alert bracelet or necklace. This alert lists your child's allergy symptoms and explains how others can provide first aid in an emergency.

Diagnosis

There's no perfect test used to confirm or rule out a food allergy. Your healthcare team will consider a few factors before making a diagnosis. These factors include:

• Your symptoms. Give your care team a detailed history of your or your child's symptoms — which foods, and how much, seem to cause problems.
• Your family history of allergies. Also share information about members of your family who have allergies of any kind.
• A physical examination. A careful exam can often identify or exclude other medical problems.

• A skin test. A skin prick test can determine whether you may react to a particular food. In this test, a small amount of the suspected food is placed on the skin of your forearm or back. A doctor or another healthcare professional then pricks your skin to allow a tiny amount of the substance beneath your skin surface.

  If you're allergic to a particular substance being tested, you develop a raised bump or reaction. However, a positive reaction to this test alone isn't enough to confirm a food allergy.

• A blood test. A blood test can measure your immune system's response to particular foods by measuring the allergy-related antibody known as immunoglobulin E (IgE).

  For this test, a blood sample taken in your care professional's office is sent to a medical laboratory. It will then be tested for foods that could have caused an allergic reaction.

• Elimination diet. You may be asked to eliminate suspect foods for a week or two and then add the food items back into your diet one at a time. This process can help link symptoms to specific foods. However, elimination diets aren't foolproof.

  An elimination diet can't tell you whether your reaction to a food is a true allergy instead of a food sensitivity. Also, if you've had a severe reaction to a food in the past, an elimination diet may not be safe.

• Oral food challenge. During this test, done in a healthcare professional's office, you'll be given small but increasing amounts of the food suspected of causing your symptoms. If you don't have a reaction during this test, you may be able to include this food in your diet again.

Treatment

One way to avoid an allergic reaction is to avoid the foods that cause symptoms. However, despite your best efforts, you may come into contact with a food that causes a reaction.

For a minor allergic reaction, prescribed antihistamines or those available without a prescription may help reduce symptoms. These drugs can be taken after exposure to an allergy-causing food to help relieve itching or hives. However, antihistamines can't treat a severe allergic reaction.

For a severe allergic reaction, you may need an emergency injection of epinephrine and a trip to the emergency room. Many people with allergies carry an epinephrine autoinjector (Adrenaclick, EpiPen). This device is a combined syringe and concealed needle that injects a single dose of medicine when pressed against your thigh.

If you've been prescribed an epinephrine autoinjector:

• Be sure you know how to use the autoinjector. Also, make sure the people closest to you know how to give the drug — if they're with you in an anaphylactic emergency, they could save your life.
• Carry it with you at all times. It may be a good idea to keep an extra autoinjector in your car or in your desk at work.
• Always be sure to replace epinephrine before its expiration date or it may not work properly.

Emerging treatments

There is ongoing research to find better treatments to reduce food allergy symptoms and prevent allergy attacks. However, there is currently no proven treatment that can prevent or completely relieve symptoms.

The U.S. Food and Drug Administration recently approved omalizumab (Xolair) to help reduce allergic reactions to multiple foods. Omalizumab is a type of drug called a monoclonal antibody. This medicine is approved for certain adults and children 1 year old or older.

Omalizumab doesn't prevent all allergic reactions to food. It also hasn't been tested to see if people with food allergy can add food allergens into their diets. Instead, omalizumab may be used as a preventive measure. Regular injections of omalizumab may reduce food allergy reactions if small amounts of a food allergen are eaten by mistake.

The first oral immunotherapy drug, Peanut (Arachis hypogaea) Allergen Powder-dnfp (Palforzia), also has been approved to treat children ages 4 to 17 years old with a confirmed peanut allergy. This medicine isn't recommended for people with uncontrolled asthma or certain conditions, including eosinophilic esophagitis.

Additional treatments currently being studied as treatments for food allergy are oral immunotherapy and sublingual immunotherapy. With these treatments, you are exposed to small doses of your food allergen. You swallow the small doses, or the doses are placed under your tongue. The dose of the allergy-provoking food is gradually increased.

Lifestyle and home remedies

One of the keys to preventing an allergic reaction is to completely avoid the food that causes your symptoms.

• Don't assume. Always read food labels to make sure they don't contain an ingredient you're allergic to. Even if you think you know what's in a food, check the label. Ingredients sometimes change.

  Food labels are required to clearly list whether the food products contain any common food allergens. Read food labels carefully to avoid the most common sources of food allergens: milk, eggs, peanuts, tree nuts, fish, shellfish, soy and wheat.

• When in doubt, say no thanks. At restaurants and social gatherings, you're always taking a risk that you might eat a food you're allergic to. Many people don't understand the seriousness of an allergic food reaction and may not realize that a tiny amount of a food can cause a severe reaction in some people.

  If you have any suspicion at all that a food may contain something you're allergic to, don't eat it.

• Involve caregivers. If your child has a food allergy, enlist the help of relatives, babysitters, teachers and other caregivers. Make sure that they understand how important it is for your child to avoid the allergy-causing food and that they know what to do in an emergency.

  It's also important to let caregivers know what steps they can take to prevent a reaction in the first place, such as careful hand-washing and cleaning any surfaces that might have come in contact with the allergy-causing food.

Coping and support

A food allergy can be a source of ongoing concern that affects life at home, school and work. Daily activities that are easy for most families, such as grocery shopping and meal preparation, can become occasions of stress for families and caregivers living with food allergies.

Keep these strategies in mind to help manage your or your child's food allergy-related stress:

• Connect with others. The opportunity to discuss food allergies and exchange information with others who share your concerns can be very helpful.

  Many internet sites and nonprofit organizations offer information and forums for discussing food allergies. Some are specifically for parents of children with food allergies. The Food Allergy Research & Education website can direct you to support groups and events in your area.

• Educate those around you. Make sure family and caregivers, including babysitters and school staff, have a thorough understanding of your child's food allergy.
• Address bullying. Children are sometimes bullied at school because of their food allergies. Discussing your child's allergy with school personnel greatly reduces your child's risk of being a bullying target.

Preparing for an appointment

Because appointments can be brief, and because there's often a lot of ground to cover, it's a good idea to be well prepared. Here's some information to help you get ready and what to expect.

• Write down any symptoms you've had, including any that may seem unrelated to the reason for which you scheduled the appointment.
• Write down key personal information, including any major stresses or recent life changes.
• Make a list of all medicines, vitamins and supplements that you're taking.
• Take a family member or friend along, if possible. Sometimes it can be difficult to remember all the information provided to you during an appointment. Someone who accompanies you may recall something that you missed or forgot.
• Write down questions to ask your care team.

Your time is limited, so preparing a list of questions will help you make the most of your time together. List your questions from most important to least important in case time runs out. Some basic questions to ask include:

• Is my condition likely caused by a food allergy or another reaction?
• What kinds of tests do I need?
• Is my condition likely temporary or long lasting?
• What types of treatment are available, and which do you recommend?
• What are the alternatives to the primary approach that you're suggesting?
• I have these other health conditions. How can I best manage these conditions together?
• Are there any dietary restrictions that I need to follow?
• Should I see a specialist? What will that cost, and will my insurance cover seeing a specialist?
• Is there a generic alternative to the medicine you're prescribing me?
• Do you have any printed material that I can take home with me? What websites do you recommend visiting?

If your child is seeing the doctor for a food allergy, you may also want to ask:

• Is my child likely to outgrow this allergy?
• Are there alternatives to the food or foods that trigger my child's allergy symptoms?
• How can I help keep my child with a food allergy safe at school?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment.

What to expect from your doctor

Your doctor is likely to ask you a few questions. Being ready to answer them may save time to go over any points you want to spend more time on. You may be asked:

• When did you begin experiencing symptoms?
• How severe were your symptoms?
• How long did it take symptoms to appear after eating the food you suspect you're allergic to?
• Did you take any nonprescription allergy medications such as antihistamines, and if so, did they help?
• Does your reaction always seem to be triggered by a certain food?
• How much food did you eat before the reaction?
• Was the food that caused the reaction cooked or raw?
• Do you know how the food was prepared?
• What, if anything, seems to improve your symptoms?
• What, if anything, appears to worsen your symptoms?

What you can do in the meantime

If you suspect you have a food allergy, avoid exposure to the food altogether until your appointment. If you do eat the food and have a mild reaction, nonprescription antihistamines may help relieve symptoms. If you have a more severe reaction and any symptoms of anaphylaxis, seek emergency help.