Food Allergies | Anaphylaxis Allergy Cause, Symptoms & Treatment

Food allergy is the most common cause of anaphylaxis outside of the hospital.1,2 Experts estimate that from 2% to 2.5% of the general population, or 5.4 million to 7 million Americans have food allergies.3 About three million of these are believed to be allergic to peanuts or tree nuts alone,3 yet there are other common food culprits.

The symptoms of food allergies resemble those of food intolerance and so it is important to consult a doctor to be diagnosed correctly. Once diagnosed, you can learn about ways to prevent and treat your food allergy.

Definition

Food allergies are an increasingly common cause of anaphylaxis that result in about 125 deaths each year in the United States.4 Some allergists believe this perceived rise in incidence may be attributed to increased exposure to certain foods, such as peanuts, before children's immune systems are mature enough to handle them.5,6

Having a food allergy, as with any other severe allergy, means that a person's immune system reacts to a protein, in this case a food protein, as a threatening foreign substance and primes the body's defenses against it. Each time the person comes in contact with this protein, his or her immune system launches an attack by releasing histamines and other powerful chemicals. The release of these chemicals trigger symptoms of an allergic reaction, which can range from hives to deadly anaphylaxis.

Histamine is a chemical released by cells of the immune system called mast cells. It is largely responsible for producing the symptoms associated with allergic reactions.

Common Culprits

There are eight types of foods that are accountable for 90% of all food-allergic reactions.7 The foods that most commonly cause anaphylaxis (called allergenic foods) are:

Peanuts
Tree nuts (walnuts, pecans, etc.)
Shellfish
Fish
Milk
Soy
Wheat
Eggs

Sulfites added to foods can also set off anaphylactic reactions, as well as exercising, within a few hours of eating for a small number of people who do not otherwise experience food-related anaphylaxis.

Children, who have immature immune systems compared with adults, are most susceptible to a broad array of food allergies. People have been known to outgrow allergies to milk, soy, and eggs after childhood. However, peanuts, tree nuts, and shellfish tend to be lifelong food triggers.5,8,9 In fact, reactions to these foods may become more serious over time. When sensitivity exists, the intensity of a given anaphylactic attack is unpredictable because it depends on the amount of allergen contained in the food eaten and the individual's degree of hypersensitivity to the allergen.8 Also, if someone already has another immune problem, he or she may be at increased risk for a strong reaction to the food to which they are allergic. For example, patients who have asthma or atopic dermatitis, as well as food allergies, are at increased risk for severe anaphylaxis.1,2,10,11

Asthma is a condition in which the airways narrow due to an allergic hypersensitivity.

Atopic dermatitis is a chronic condition resulting in itchy inflammation of the skin that is associated with allergy sufferers.

Symptoms

Symptoms of food allergies can range from mildly irritating to life threatening. The most common symptoms of food allergies are:

Hives
Vomiting
Diarrhea
Abdominal cramping
Other symptoms typical of anaphylaxis generally include:

Swelling of the throat, lips, or tongue
Difficulty breathing or swallowing
Metallic taste or itching in the mouth
Generalized flushing, itching, or redness of the skin (hives)
Nausea
Increased heart rate
Plunging blood pressure (and accompanying paleness)
Sudden feeling of weakness
Anxiety or an overwhelming sense of doom
Collapse
Loss of consciousness

For some people with food allergies, just a taste or even a touch of the foods to which they are allergic can result in any of these symptoms and can set off a chain reaction that takes only minutes to culminate in full-blown anaphylaxis: swelling of the airways, loss of blood pressure, loss of consciousness, shock, and even death.12 This can happen with their first known exposure to a food. There have even been rare cases documented in which inhalation exposure to a food has triggered an anaphylactic reaction.13 The more rapidly symptoms present themselves; the more likely the reaction is to be severe.13

Intolerance Versus Allergy

Food allergy and intolerance are often mistaken for one another. While they may share similar symptoms, including diarrhea and vomiting, food allergy is an immune system response while food intolerance occurs when another system of the body (usually the digestive tract) reacts adversely to a food.

For example, one of the most common food intolerances arises in response to lactose, the sugar in milk. Lactose intolerance occurs when a person lacks an enzyme needed to digest this sugar, and the body reacts with gas, bloating, diarrhea, and abdominal pain when milk products containing lactose are consumed. When these symptoms occur as a result of intolerance rather than allergy, they do not indicate an anaphylactic reaction. However, anyone who has such symptoms should seek proper medical care to get a diagnosis and counseling in order to determine what dietary and medical measures are needed.

Diagnosis

A person who has experienced even mild allergic reactions to food should seek a professional diagnosis by a board-certified allergist (see Find an Allergist to locate an allergist near you). To make a proper diagnosis, the allergist will record a complete history of the symptoms, which foods were eaten, how much of the food was eaten, and how soon afterward the symptoms began. The doctor may also decide to perform a skin prick test, RAST (blood test), or oral food challenge to confirm the diagnosis.

A skin prick test may be used to identify allergens. This test involves injecting tiny amounts of diluted food solutions into the skin. If the person is allergic to the particular food sample injected, then the skin will react within 15 to 20 minutes—usually with a hive-like swelling surrounded by redness.

RAST, or radioallergosorbent test, directly measures antibodies specific to allergens in the blood.

Prevention and Treatment

In most cases, there is no cure for food allergies. Therefore, it is essential that people with food allergies protect themselves by carefully avoiding the foods that trigger their reactions, and by being prepared to treat anaphylactic reactions that occur immediately with epinephrine in combination with emergency medical care.

Avoidance

Avoidance of foods that trigger allergic reactions is critical and more challenging than one might expect. While steering clear of a food in its isolated form may not be so difficult, people with allergies, or the parents of children with food allergies, must know to check product labels for alternate names of food ingredients that may contain their allergens. People who have food allergies must also try to avoid foods that may contain hidden ingredients or that may have been prepared using equipment contaminated by an allergenic food.

Since it is often difficult to avoid hidden foods—and because it is often difficult for children to resist sharing foods—it's important that an allergic person's family, friends, and teachers know about, and understand, the ramifications of food allergy, so they can aid in the prevention of anaphylaxis and be ready to assist should an emergency arise.

Epinephrine

Exposure to allergenic foods is sometimes unavoidable, so people with food allergies need to be prepared to treat allergic reactions. The treatment of choice for severe allergic reactions to food, which can swiftly lead to anaphylaxis, is an immediate injection of epinephrine followed by emergency medical attention.14 Many physicians also recommend taking antihistamines such as diphenhydramine to relieve the symptoms of allergic reactions, but antihistamines are not a substitute for epinephrine. Only epinephrine can stop the potentially deadly effects of anaphylaxis.

A 1992 study of children and adolescents with food allergy demonstrates how important it is for people with food allergies to carry epinephrine at all times.10 According to the study, 10 out of 13 fatal and near-fatal anaphylactic reactions to food occurred in public places, and none of the adolescents and children who died had epinephrine with them. All of the adolescents and children who survived received epinephrine before or within 5 minutes of developing severe symptoms.10 Other studies agree with these findings.11 Thus, all individuals with food allergies should carry self-injectable epinephrine, such as the EpiPen® or EpiPen® Jr auto-injector, with them at all times.

Since immediate administration of epinephrine can be the difference between life and death, parents of children with life-threatening food allergies should alert their child's school of the particular allergen, and make sure their child's teachers and caregivers have an epinephrine auto-injector on hand and know how to administer it.

Side effects of epinephrine may include palpitations, tachycardia (an abnormally fast heartbeat), sweating, nausea and vomiting, and respiratory difficulty. Cardiac arrhythmias may follow administration of epinephrine. Therefore, patients should ask their doctors about the circumstances under which this life-saving medication should be used.

You and your child should also ask your physicians whether antihistamines should be carried in addition to epinephrine. Wearing a medical identification bracelet describing your allergies and susceptibility to anaphylaxis can help ensure prompt, proper treatment during an emergency.

Emergency medical care

Even after administering epinephrine, emergency medical treatment should be sought at once because severely allergic people experiencing anaphylaxis may need emergency respiratory or cardiac care, or even need to be resuscitated if they stop breathing altogether. More commonly, these patients will need professional care to determine whether additional epinephrine, steroids, antihistamines, or other treatments are required. In either case, follow-up diagnosis and care by medical professionals after administration of epinephrine is critical to recovery. Delayed or secondary reactions do occur, and patients should remain under medical supervision for at least 4 hours after an episode of anaphylaxis.