Many people who think they are allergic to a food may actually be intolerant to it. Some of the symptoms of food intolerance and food allergy are similar, but the differences between the two are very important. If you are allergic to a food, this allergen triggers a response in the immune system. Food allergy reactions can be life-threatening, so people with this type of allergy must be very careful to avoid their food triggers.

Eight foods are responsible for the majority of allergic reactions:
•    Cow’s milk
•    Eggs
•    Fish
•    Peanuts
•    Shellfish
•    Soy
•    Tree nuts
•    Wheat

Being allergic to a food may also result in being allergic to a similar protein found in something else. For example, if you are allergic to ragweed, you may also develop reactions to bananas or melons. This is known as cross-reactivity. Cross-reactivity happens when the immune system thinks one protein is closely related to another. When foods are involved it is called oral allergy syndrome (OAS).

Food allergy can strike children and adults alike. While many children outgrow a food allergy, it is also possible for adults to develop allergies to particular foods.

Food Protein-Induced Enterocolitis Syndrome (FPIES), sometimes referred to as a delayed food allergy, is a severe condition causing vomiting and diarrhea. In some cases, symptoms can progress to dehydration and shock brought on by low blood pressure and poor blood circulation.

Much like other food allergies, FPIES allergic reactions are triggered by ingesting a food allergen. Although any food can be a trigger, the most common culprits include milk, soy and grains. FPIES often develops in infancy, usually when a baby is introduced to solid food or formula.

Eosinophilic (ee-uh-sin-uh-fil-ik) Esophagitis (EoE) is an allergic condition causing inflammation of the esophagus. The esophagus is the tube that sends food from the throat to the stomach. Most research suggests that the leading cause of EoE is an allergy or a sensitivity to particular proteins found in foods. Many people with EoE have a family history of allergic disorders such as asthma, rhinitis, dermatitis or food allergy.

For most people, celebrations are fun events. But for parents of food allergic children, or even for food allergic adults, activities involving food can be filled with worry. This is because coming in contact with a food allergen has the potential to cause a very serious allergic reaction.

Allergies are the result of a reaction that starts in the immune system. For instance, if you have an allergy to eggs, your immune system identifies a protein found in eggs as an allergen. Your immune system reacts by producing antibodies called Immunoglobulin E (IgE). These antibodies attach to cells in your skin, lungs and gastrointestinal (GI) tract. If you come in contact with the allergen again, the cells release chemicals including histamine, which cause food allergy symptoms such as itching, hives, swelling, diarrhea, wheezing and a potentially life-threatening reaction called anaphylaxis (an-a-fi-LAK-sis). Without immediate treatment—an injection of epinephrine and expert care in a hospital—anaphylaxis can be fatal.

There is a difference between food allergy and food intolerance. A food allergy involves the immune system while food intolerance, such as lactose intolerance, does not. Food intolerance typically involves the GI tract, causing uncomfortable symptoms like abdominal pain, nausea, vomiting and diarrhea, but there is no risk of anaphylaxis.

Common Food Allergens
The most common food allergens are the proteins in cow’s milk, eggs, peanuts, wheat, soy, fish, shellfish and tree nuts. In some food groups, especially tree nuts and seafood, an allergy to one member of a food family may result in the person being allergic to other members of the same group. This is known as cross-reactivity. Cross-reactivity for other food families is not common.

Most food allergens can cause allergic reactions even after they are cooked or have undergone digestion in the intestines, although research is showing that more than half of children with milk and egg allergies can tolerate extensively heated milk and egg in baked foods. Some allergens (usually fruits and vegetables) cause allergic reactions in people with a pollen allergy but only if eaten in raw form. Symptoms in these cases are usually limited to the mouth and throat.

Most symptoms of food allergy occur within 2 hours at the most, but within the past few years a new type of food allergy has been discovered called alpha gal, with symptoms that may be delayed by 4-8 hours, often awakening the person at night. This allergy is to galactose-alpha, 1,3-galactose, a carbohydrate found on mammalian meat, and is associated with being bitten by the Lone Star tick. People with alpha gal allergy should avoid beef, lamb, pork and venison.

Diagnosing Food Allergies
An allergist / immunologist, often referred to as an allergist, has specialized training and expertise to determine if your symptoms are caused by a food allergy or due to other food-related disorders such as food protein-induced enterocolitis syndrome (FPIES) or eosinophilic esophagitis (EoE).

Your allergist will take a thorough medical history, followed by a physical examination. You will be asked about the foods you eat, the frequency, severity and nature of your symptoms, and the amount of time between eating a food and any reaction.

Allergy skin tests may determine which foods, if any, trigger your allergic symptoms. In skin testing, a small amount of extract made from the food is placed on the back or arm. If a raised bump or small hive develops within 20 minutes, it indicates a possible allergy. If it does not develop, the test is negative. It is uncommon for someone with a negative skin test to have an IgE-mediated food allergy.

In certain cases, such as in patients with severe eczema, an allergy skin test cannot be done. Your doctor may recommend an IgE blood test. False positive results may occur with both skin and blood testing. IgG blood testing is not recommended, as it is unproven in diagnosing food allergies. Oral food challenges can confirm the diagnosis and are done by consuming the food in a medical setting to determine if it causes a reaction. Food challenges should not take place at home.

Treating Food Allergies
There is currently no cure for food allergy, but there are many promising treatments under investigation. Avoidance, education and preparedness are the keys to managing food allergy.

While exposure to airborne food allergens (e.g., from cooking vapors) usually does not result in anaphylaxis, it can cause a runny nose and itchy eyes similar to a reaction from coming in contact with pollen. However, eating even a small amount of the food, such as that left on cooking utensils or from a food processing facility, can cause a life-threatening reaction. This is why reading the ingredients on food labels and asking questions about prepared foods are an essential part of avoidance plans.

People with food allergy should always carry auto-injectable epinephrine to be used in the event of an anaphylactic reaction. Symptoms of anaphylaxis may include difficulty breathing, dizziness or loss of consciousness. If you have any of these symptoms in the context of eating, use the epinephrine auto-injector and immediately call 911. Don’t wait to see if your symptoms go away or get better on their own.

Outgrowing Food Allergies
Most children outgrow their allergies to cow’s milk, egg, soy and wheat, even if they have a history of a severe reaction. However,peanut, tree nut fish and shellfish allergy tends to persist through adulthood. Repeat allergy testing with your allergist can help you learn when you or your child’s food allergies are resolving with time.

Healthy Tips
• Always ask about ingredients when eating at restaurants or when you are eating foods prepared by family or friends.
• Carefully read food labels. The United States and many other countries require that major food allergens are to be listed in common language (milk, egg, fish, shellfish, tree nuts, wheat, peanuts and soybeans).
• Carry and know how to use auto-injectable epinephrine and antihistamines to treat emergency reactions. Teach family members and other people close to you how to use epinephrine and consider wearing a medical alert bracelet that describes your allergy. If a reaction occurs, have someone take you to the emergency room, even if symptoms subside. Afterwards, get follow-up care from your allergist.