Food allergy

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.

If you are allergic to:	Birch pollen	Ragweed pollen	Grasses	Mugwort pollen
You also may have a reaction to:	Almond Apple Apricot Carrot Celery Cherry Hazelnut Peach Peanut Pear Plum Raw potato Soybean Some herbs and spices (anise, caraway seed, coriander, fennel, parsley)	Banana Cucumber Melon (cantaloupe, honeydew and watermelon) Zucchini	Kiwi Melon (cantaloupe, honeydew and watermelon) Orange Peanut Tomato White potato Zucchini	Apple Bell pepper Broccoli Cabbage Carrot Cauliflower Celery Garlic Onion Peach Some herbs and spices (anise, black pepper, caraway seed, coriander, fennel, mustard, parsley)

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.