Allergy Types: Food Allergies: Food Allergies and Food Intolerance
A food allergy is an adverse immune response to certain kinds of food.
They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions.
The protein in the food is the most common allergic component. These kinds of allergies occur when the body’s immune system mistakenly identifies a protein as harmful. Some proteins or fragments of proteins are resistant to digestion and those that are not broken down in the digestive process are tagged by the Immunoglobulin E (IgE). These tags fool the immune system into thinking that the protein is an invader. The immune system, thinking the organism (the individual) is under attack, sends white blood cells to attack, and that triggers an allergic reaction. These reactions can range from mild to severe. Allergic responses include dermatitis,gastrointestinal and respiratory distress, including such life-threatening anaphylactic responses as biphasic anaphylaxis andvasodilation; these require immediate emergency intervention. Individuals with protein allergies commonly avoid contact with the problematic protein. Some medications may prevent, minimize or treat protein allergy reactions. There is no cure.
Treatment consists of either immunotherapy (desensitisation) or avoidance, in which the allergic person avoids all forms of contact with the food to which they are allergic. Areas of research include anti-IgE antibody (omalizumab, or Xolair) and specific oral tolerance induction (SOTI), which have shown some promise for treatment of certain food allergies. People diagnosed with a food allergy may carry an injectable form of epinephrine such as an EpiPen, or wear some form of medical alert jewelry, or develop an emergency action plan, in accordance with their doctor.
The scope of the problem, particularly for young people, is a significant public health issue.
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:
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.
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.
- A past food allergy. Children may outgrow a food allergy, but in some cases it returns later in life.
- Other allergies. If you’re already allergic to one food, you may be at increased risk of becoming allergic to another. Likewise, 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 most common in children, especially toddlers and infants. As you grow older, your digestive system matures and your body is less likely to absorb food or 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
- Waiting longer to use epinephrine to treat your food allergy symptoms
- Not having hives or other skin symptoms
Suspected food allergies should always be evaluated, diagnosed, and treated by a qualified medical professional, such as a board-certified allergist. Your primary care provider may refer you to an allergist. You may also search the physician directory maintained by the American Academy of Allergy, Asthma & Immunology.
Do not diagnose a food allergy on your own. Self-diagnosis can lead to unnecessary dietary restrictions and inadequate nutrition, especially in children. Additionally, some people think they are allergic to a food when they actually have another type of food disorder, and treatment may differ.
Some methods of food allergy testing are unproven and are considered controversial, since no definitive studies have shown that they can effectively diagnose food allergies. Some may even increase the risk of an allergic reaction. Learn more about unproven diagnostic food allergy testing >
The first step an allergist will take to diagnose a food allergy is a thorough medical history. The allergist will ask questions to determine if food allergy may be causing your symptoms and to identify the culprit food(s), and will then perform a physical exam.
Next, the allergist may conduct tests to help identify a food allergy. While these tests alone do not always provide clear-cut answers, the allergist will combine your test results with the information given in your medical history to provide a diagnosis. These tests may include:
- Skin prick test
- Blood test
- Oral food challenge
- Trial elimination diet
These tests are all proven diagnostic methods. Depending on your medical history and initial test results, you may have to take more than one test before receiving your diagnosis.
Guidelines for the Diagnosis and Management of Food Allergy in the United States, published by the National Institute of Allergy and Infectious Diseases (NIAID), is an excellent resource. Developed by a panel of prominent food allergy experts, along with 34 professional organizations, federal agencies and patient advocacy groups, this document provides the most up-to-date clinical advice on caring for people with food allergies.
The only way to avoid an allergic reaction is to avoid the foods that cause signs and symptoms. However, despite your best efforts, you may come into contact with a food that causes a reaction.
For a minor allergic reaction,over-the-counter or prescribed antihistamines 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 (EpiPen, Twinject, Auvi-Q). This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh.
If your doctor has prescribed an epinephrine autoinjector:
- Be sure you know how to use the autoinjector. Also, make sure the people closest to you know how to administer 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.
While there’s ongoing research to find better treatments to reduce food allergy symptoms and prevent allergy attacks, there isn’t any proven treatment that can prevent or completely relieve symptoms. Unfortunately, allergy shots (immunotherapy), a series of injections used to reduce the effect of other allergies such as hay fever, aren’t effective for treating food allergies.
Two treatments being studied are:
- Anti-IgE therapy. The medication omalizumab (Xolair) interferes with the body’s ability to use IgE. The drug is currently being studied for treatment of allergic asthma and food allergies. However, this treatment is still considered experimental, and more research needs to be done on the drug’s long-term safety. It has been associated with a potential increased risk of anaphylaxis.
- Oral immunotherapy. Researchers have been studying the use of oral immunotherapy (OIT) as a treatment for food allergy. Small doses of the food you’re allergic to are swallowed or placed under your tongue (sublingual). The dose of the allergy-provoking food is gradually increased. Initial results look promising, even in people with peanut allergy. But more research needs to be done to ensure that this treatment is safe.
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 a greater hardship. 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 doctor about prescribing emergency epinephrine. You may need to carry an epinephrine autoinjector (EpiPen, Twinject, Auvi-Q) 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.
If your child has a food allergy, take these precautions to ensure his or her safety:
- Notify key people that your child has a food allergy. Talk with child care 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 he or she 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 he or she 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.
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 they 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, steer clear.
- Involve caregivers. If your child has a food allergy, enlist the help of relatives, baby sitters, teachers and other caregivers. Make sure 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.
Most people with food allergies do well if they are able to avoid their trigger foods. With time, many people lose their antibodies to the foods to which they once were allergic to, or “outgrow” the allergy.
- This is most likely to happen if the trigger food is identified and eliminated from the diet.
- This is especially true in children who, by about the age of 10 years, may outgrow their allergies — mainly to milk and eggs.
- Allergies to nuts, fish, and shellfish can last a lifetime.
Once a person has had a reaction to a food, he or she is more likely to have a severe reaction if exposed to the trigger
Complications of food allergy can include:
- Anaphylaxis. This is a life-threatening allergic reaction.
- Atopic dermatitis (eczema). Food allergy may cause a skin reaction, such as eczema.
- Migraines. Histamines, released by your immune system during an allergic reaction, have been shown to trigger migraines in some people.