Types of Allergies

Food Allergies

An allergy occurs when your body’s natural defenses overreact to exposure to a particular substance, treating it as an invader and sending out chemicals to defend against it.

Overview

More than 50 million Americans have an allergy of some kind. Food allergies are estimated to affect 4 to 6 percent of children and 4 percent of adults, according to the Centers for Disease Control and Prevention.

Food allergy symptoms are most common in babies and children, but they can appear at any age. You can even develop an allergy to foods you have eaten for years with no problems. Learn more about the types of food allergies.

Symptoms

The body’s immune system keeps you healthy by fighting off infections and other dangers to good health. A food allergy reaction occurs when your immune system overreacts to a food or a substance in a food, identifying it as a danger and triggering a protective response.

While allergies tend to run in families, it is impossible to predict whether a child will inherit a parent’s food allergy or whether siblings will have a similar condition. Some research does suggest that the younger siblings of a child with a peanut allergy will also be allergic to peanuts.  

Symptoms of a food allergy can range from mild to severe. Just because an initial reaction causes few problems doesn’t mean that all reactions will be similar; a food that triggered only mild symptoms on one occasion may cause more severe symptoms at another time.

The most severe allergic reaction is anaphylaxis — a life-threatening whole-body allergic reaction that can impair your breathing, cause a dramatic drop in your blood pressure and affect your heart rate. Anaphylaxis can come on within minutes of exposure to the trigger food. It can be fatal and must be treated promptly with an injection of epinephrine (adrenaline).

While any food can cause an adverse reaction, eight types of food account for about 90 percent of all reactions:

Certain seeds, including sesame and mustard seeds (the main ingredient in the condiment mustard), also are common food allergy triggers and considered a major allergen in some countries.

Symptoms of an allergic reaction may involve the skin, the gastrointestinal tract, the cardiovascular system and the respiratory tract. They can surface in one or more of the following ways:

  • Vomiting and/or stomach cramps
  • Hives
  • Shortness of breath
  • Wheezing
  • Repetitive cough
  • Shock or circulatory collapse
  • Tight, hoarse throat; trouble swallowing
  • Swelling of the tongue, affecting the ability to talk or breathe
  • Weak pulse
  • Pale or blue coloring of skin
  • Dizziness or feeling faint
  • Anaphylaxis, a potentially life-threatening reaction that can impair breathing and send the body into shock; reactions may simultaneously affect different parts of the body (for example, a stomachache accompanied by a rash)

Most food-related symptoms occur within two hours of ingestion; often they start within minutes. In some very rare cases, the reaction may be delayed by four to six hours or even longer. Delayed reactions are most typically seen in children who develop eczema as a symptom of food allergy and in people with a rare allergy to red meat caused by the bite of a lone star tick.
Another type of delayed food allergy reaction stems from food protein-induced enterocolitis syndrome (FPIES), a severe gastrointestinal reaction that generally occurs two to six hours after consuming milk, soy, certain grains and some other solid foods. It mostly occurs in young infants who are being exposed to these foods for the first time or who are being weaned. FPIES often involves repetitive vomiting and can lead to dehydration. In some instances, babies will develop bloody diarrhea. Because the symptoms resemble those of a viral illness or bacterial infection, diagnosis of FPIES may be delayed. FPIES is a medical emergency that should be treated with IV rehydration.

Not everyone who experiences symptoms after eating certain foods has a food allergy or needs to avoid that food entirely; for instance, some people experience an itchy mouth and throat after eating a raw or uncooked fruit or vegetable. This may indicate oral allergy syndrome - a reaction to pollen, not to the food itself. The immune system recognizes the pollen and similar proteins in the food and directs an allergic response to it. The allergen is destroyed by heating the food, which can then be consumed with no problem.

Triggers

Once a food allergy is diagnosed, the most effective treatment is to avoid the food. The foods most associated with food allergy in children are:

  • Milk
  • Eggs
  • Peanuts

Children may outgrow their allergic reactions to milk and to eggs. Peanut and tree nut allergies are likely to persist.

The most common food allergens in adults are:

  • Fruit and vegetable pollen (oral allergy syndrome)
  • Peanuts and tree nuts
  • Fish and shellfish

People allergic to a specific food may also potentially have a reaction to related foods. A person allergic to one tree nut may be cross-reactive to others. Those allergic to shrimp may react to crab and lobster. Someone allergic to peanuts - which actually are legumes (beans), not nuts - may have problems with tree nuts, such as pecans, walnuts, almonds and cashews; in very rare circumstances they may have problems with other legumes (excluding soy).

Learning about patterns of cross-reactivity and what must be avoided is one of the reasons why people with food allergies should receive care from a board-certified allergist. Determining if you are cross-reactive is not straightforward. Allergy testing to many items in the same “family” may not be specific enough - many times, these tests are positive, given how similar two food items in a “family” may look to the test. If you have tolerated it well in the past, a food that is theoretically cross-reactive may not have to be avoided at all.

Negative tests may be very useful in ruling out an allergy. In the case of positive tests to foods that you have never eaten but that are related to items to which you’ve had an allergic reaction, an oral food challenge is the best way to determine whether the food poses a danger.

Diagnosing Food Allergies

A food allergy will usually cause some sort of reaction every time the trigger food is eaten. Symptoms can vary from person to person, and you may not always experience the same symptoms during every reaction. Allergic reactions to food can affect the skin, respiratory tract, gastrointestinal tract and cardiovascular system. It is impossible to predict how severe the next reaction might be, and all patients with food allergies should be carefully counseled about the risk of anaphylaxis, a potentially fatal reaction that is treated with epinephrine (adrenaline).

While food allergies may develop at any age, most appear in early childhood. If you suspect a food allergy, see an allergist, who will take your family and medical history, decide which tests to perform (if any) and use this information to determine if a food allergy exists.

To make a diagnosis, allergists ask detailed questions about your medical history and your symptoms. Be prepared to answer questions about:

  • What and how much you ate
  • How long it took for symptoms to develop
  • What symptoms you experienced and how long they lasted.

After taking your history, your allergist may order skin tests and/or blood tests, which indicate whether food-specific immunoglobulin E (IgE) antibodies are present in your body:

  • Skin-prick tests provide results in about 20 minutes. A liquid containing a tiny amount of the food allergen is placed on the skin of your arm or back. Your skin is pricked with a small, sterile probe, allowing the liquid to seep under the skin. The test, which isn’t painful but can be uncomfortable, is considered positive if a wheal (resembling the bump from a mosquito bite) develops at the site where the suspected allergen was placed. As a control, you’ll also get a skin prick with a liquid that doesn’t contain the allergen; this should not provoke a reaction, allowing comparison between the two test sites.
  • Blood tests, which are a bit less exact than skin tests, measure the amount of IgE antibody to the specific food(s) being tested. Results are typically available in about a week and are reported as a numerical value.

Your allergist will use the results of these tests in making a diagnosis. A positive result does not necessarily indicate that there is an allergy, though a negative result is useful in ruling one out.

In some cases, an allergist may wish to conduct an oral food challenge, which is considered the most accurate way to make a food allergy diagnosis. During an oral food challenge, which is conducted under strict medical supervision, the patient is fed tiny amounts of the suspected trigger food in increasing doses over a period of time, followed by a few hours of observation to see if a reaction occurs. This test is helpful when the patient history is unclear or if the skin or blood tests are inconclusive. It also can be used to determine if an allergy has been outgrown.

Because of the possibility of a severe reaction, an oral food challenge should be conducted only by experienced allergists in a doctor’s office or at a food challenge center, with emergency medication and equipment on hand.

Management and Treatment

The primary way to manage a food allergy is to avoid consuming the food that causes you problems. Carefully check ingredient labels of food products, and learn whether what you need to avoid is known by other names.

The Food Allergy Labeling and Consumer Protection Act of 2004 (FALCPA) mandates that manufacturers of packaged foods produced in the United States identify, in simple, clear language, the presence of any of the eight most common food allergens - milk, egg, wheat, soy, peanut, tree nut, fish and crustacean shellfish - in their products. The presence of the allergen must be stated even if it is only an incidental ingredient, as in an additive or flavoring.

Some goods also may be labeled with precautionary statements, such as “may contain,” “might contain,” “made on shared equipment,” “made in a shared facility” or some other indication of potential allergen contamination. There are no laws or regulations requiring those advisory warnings and no standards that define what they mean. If you have questions about what foods are safe for you to eat, talk with your allergist.   

Be advised that the FALCPA labeling requirements do not apply to items regulated by the U.S. Department of Agriculture (meat, poultry and certain egg products) and those regulated by the Alcohol and Tobacco Tax and Trade Bureau (distilled spirits, wine and beer). The law also does not apply to cosmetics, shampoos and other health and beauty aids, some of which may contain tree nut extracts or wheat proteins.

Avoiding an allergen is easier said than done. While labeling has helped make this process a bit easier, some foods are so common that avoiding them is daunting. A dietitian or a nutritionist may be able to help. These food experts will offer tips for avoiding the foods that trigger your allergies and will ensure that even if you exclude certain foods from your diet, you still will be getting all the nutrients you need. Special cookbooks and support groups, either in person or online, for patients with specific allergies can also provide useful information.

Many people with food allergies wonder whether their condition is permanent. There is no definitive answer. Allergies to milk, eggs, wheat and soy may disappear over time, while allergies to peanuts, tree nuts, fish and shellfish tend to be lifelong.  

Eating out

Be extra careful when eating in restaurants. Waiters (and sometimes the kitchen staff) may not always know the ingredients of every dish on the menu. Depending on your sensitivity, even just walking into a kitchen or a restaurant can cause an allergic reaction.

Consider using a “chef card” - available through many websites - that identifies your allergy and what you cannot eat. Always tell your servers about your allergies and ask to speak to the chef, if possible. Stress the need for preparation surfaces, pans, pots and utensils that haven’t been contaminated by your allergen, and clarify with the restaurant staff what dishes on the menu are safe for you.

Anaphylaxis

Symptoms caused by a food allergy can range from mild to life-threatening; the severity of each reaction is unpredictable. People who have previously experienced only mild symptoms may suddenly experience a life-threatening reaction called anaphylaxis, which can, among other things, impair breathing and cause a sudden drop in blood pressure. This is why allergists do not like to classify someone as “mildly” or “severely” food allergic - there is just no way to tell what may happen with the next reaction. In the U.S., food allergy is the leading cause of anaphylaxis outside the hospital setting.

Epinephrine (adrenaline) is the first-line treatment for anaphylaxis, which results when exposure to an allergen triggers a flood of chemicals that can send your body into shock. Anaphylaxis can occur within seconds or minutes of exposure to the allergen, can worsen quickly and can be fatal.

Once you’ve been diagnosed with a food allergy, your allergist should prescribe an epinephrine auto-injector and teach you how to use it. You should also be given a written treatment plan describing what medications you’ve been prescribed and when they should be used. Check the expiration date of your auto-injector, note the expiration date on your calendar and ask your pharmacy about reminder services for prescription renewals.

Anyone with a food allergy should always have his or her auto-injector close at hand. Be sure to have two doses available, as the severe reaction can recur in about 20 percent of individuals. There are no data to help predict who may need a second dose of epinephrine, so this recommendation applies to all patients with a food allergy.

Use epinephrine immediately if you experience severe symptoms such as shortness of breath, repetitive coughing, weak pulse, hives, tightness in your throat, trouble breathing or swallowing, or a combination of symptoms from different body areas, such as hives, rashes or swelling on the skin coupled with vomiting, diarrhea or abdominal pain. Repeated doses may be necessary. You should call for an ambulance (or have someone nearby do so) and inform the dispatcher that epinephrine was administered and more may be needed. You should be taken to the emergency room; policies for monitoring patients who have been given epinephrine vary by hospital.

If you are uncertain whether a reaction warrants epinephrine, use it right away; the benefits of epinephrine far outweigh the risk that a dose may not have been necessary.

Common side effects of epinephrine may include anxiety, restlessness, dizziness and shakiness. In very rare instances, the medication can lead to abnormal heart rate or rhythm, heart attack, a sharp increase in blood pressure and fluid buildup in the lungs. If you have certain pre-existing conditions, such as heart disease or diabetes, you may be at a higher risk for adverse effects from epinephrine. Still, epinephrine is considered very safe and is the most effective medicine to treat severe allergic reactions.

Other medications may be prescribed to treat symptoms of a food allergy, but it is important to note that there is no substitute for epinephrine: It is the only medication that can reverse the life-threatening symptoms of anaphylaxis.

Managing food allergies in children

Because fatal and near-fatal food allergy reactions can occur at school or other places outside the home, parents of a child with food allergies need to make sure that their child’s school has a written emergency action plan. The plan should provide instructions on preventing, recognizing and managing food allergies and should be available in the school and during activities such as sporting events and field trips. If your child has been prescribed an auto-injector, be sure that you and those responsible for supervising your child understand how to use it.

In November 2013, President Barack Obama signed into law the School Access to Emergency Epinephrine Act (PL 113-48), which encourages states to adopt laws requiring schools to have epinephrine auto-injectors on hand. As of late 2014, dozens of states had passed laws that either require schools to have a supply of epinephrine auto-injectors for general use or allow school districts the option of providing a supply of epinephrine. Many of these laws are new, and it is uncertain how well they are being implemented. As a result, ACAAI still recommends that providers caring for food-allergic children in states with such laws maintain at least two units of epinephrine per allergic child attending the school.

Can food allergies be prevented?

In 2013, the American Academy of Pediatrics published a study that supported earlier research suggesting that feeding solid foods to very young babies could promote allergies. It recommends against introducing solid foods to babies younger than 17 weeks. It also suggests exclusively breast-feeding “for as long as possible,” but stops short of endorsing earlier research supporting six months of exclusive breast-feeding.

Research on the benefits of feeding hypoallergenic formulas to high-risk children - those born into families with a strong history of allergic diseases - is mixed.

The timing of introduction of certain foods is also being investigated as a means of prevention. The general practice in the United States and other Western countries is to delay the introduction of highly allergenic foods, such as peanuts, tree nuts and seafood, until after age 3. There is newer but not yet proven data suggesting that introducing these foods in a baby’s first year may help the child tolerate the food.

The bottom line is that the timing of when to introduce foods remains confusing and somewhat controversial.

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