Food allergies are a growing concern, affecting millions worldwide. Understanding what triggers these allergies is crucial for effective management and prevention. After a food allergy is diagnosed, the most effective treatment is to avoid the food.
This guide delves into the most common food allergies, explores cross-reactivity, and provides insights on diagnosis, management, and emergency treatment.
Common Food Allergens: Children vs. Adults
The foods most often associated with food allergies differ between children and adults.
In children, the most common food allergens are:
- Milk
- Eggs
- Peanuts
Childhood food allergies: Milk, eggs, and peanuts are the most prevalent allergens among children, often requiring careful dietary management.
While some children may outgrow their allergies to milk and eggs, peanut and tree nut allergies are more likely to persist throughout their lives.
In adults, the most common food allergens are:
- Fruit and vegetable pollen (oral allergy syndrome)
- Peanuts and tree nuts
- Fish and shellfish
Adult food allergies: Common triggers include fruit and vegetable pollen, peanuts, tree nuts, fish, and shellfish, necessitating vigilance in food choices and preparation.
Understanding Cross-Reactivity
Individuals allergic to a specific food may also experience reactions to related foods due to cross-reactivity. For example, someone allergic to one type of tree nut might react to others. Similarly, those allergic to shrimp could react to crab and lobster. People allergic to peanuts—which are legumes, not nuts—may experience problems with tree nuts like pecans, walnuts, almonds, and cashews. In rare cases, they may also react to other legumes, excluding soy.
Navigating these patterns of cross-reactivity requires guidance from a board-certified allergist. Determining cross-reactivity isn’t always straightforward. Allergy testing for multiple items within the same “family” may lack specificity. These tests often yield positive results because similar food items in a “family” can appear alike to the test. If a theoretically cross-reactive food has been tolerated well in the past, it might not need to be avoided.
Negative tests can be helpful in ruling out allergies. For foods never eaten but related to items causing allergic reactions, an oral food challenge is the best way to determine if the food poses a danger.
Allergy Testing and Diagnosis
A food allergy usually triggers a reaction each time the trigger food is consumed. Symptoms can vary from person to person, and the same individual may not always experience identical symptoms during each reaction. Allergic reactions to food can affect the skin, respiratory tract, gastrointestinal tract, and cardiovascular system. Predicting the severity of the next reaction is impossible, so all patients with food allergies should be carefully counseled about the risk of anaphylaxis, a potentially fatal reaction treated with epinephrine (adrenaline).
Food allergies can develop at any age, but most appear in early childhood. If you suspect a food allergy, consult an allergist. They will take your family and medical history to decide which tests to perform (if any) and determine if a food allergy exists.
To make a diagnosis, allergists ask detailed questions about your medical history and symptoms, including:
- 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 to check for food-specific immunoglobulin E (IgE) antibodies in your body:
- Skin-prick tests: These 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. The skin is pricked with a small, sterile probe, allowing the liquid to seep under the skin. The test is considered positive if a wheal (resembling a mosquito bite bump) develops at the site where the suspected allergen was placed. A control skin prick with a liquid that doesn’t contain the allergen should not provoke a reaction, allowing comparison between the two test sites.
- Blood tests: These tests, which are slightly less precise 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 these test results to make a diagnosis. A positive result does not necessarily indicate an allergy, although a negative result is useful in ruling one out.
In some cases, an allergist will recommend an oral food challenge, considered the most accurate way to diagnose a food allergy. During this challenge, conducted under strict medical supervision, the patient is fed tiny amounts of the suspected trigger food in increasing doses over time, followed by 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 can also determine if an allergy has been outgrown.
Because of the potential for severe reactions, oral food challenges should only be conducted by experienced allergists in a doctor’s office or at a food challenge center, with emergency medication and equipment available.
Management and Treatment Strategies
The primary way to manage a food allergy is to avoid consuming the food that causes 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, such as in an additive or flavoring.
Some goods may also be labeled with precautionary statements like “may contain,” “might contain,” “made on shared equipment,” or “made in a shared facility,” indicating potential allergen contamination. However, no laws or regulations require these advisory warnings, and there are no standards that define what they mean.
Avoiding an allergen is challenging, but labeling has made it easier. Some foods are so common that avoiding them can be daunting. A dietitian or nutritionist can offer tips for avoiding trigger foods and ensure you still get the necessary nutrients. Special cookbooks and support groups for patients with specific allergies can also provide helpful information.
Many wonder if food allergies are permanent. The answer varies. Allergies to milk, eggs, wheat, and soy may disappear over time, while allergies to peanuts, tree nuts, fish, and shellfish tend to be lifelong.
Omalizumab (Xolair) is a prescription injection that can help reduce allergic reactions to food in people 1 year of age and older. It is not approved for emergency treatment of allergic reactions such as anaphylaxis. Xolair targets immunoglobulin E (IgE), an underlying cause of food allergy reactions. It’s intended for repeated use to reduce the risk of allergic reactions and patients who take Xolair must continue to avoid foods to which they are allergic.
Eating Out Safely
Be extra cautious when eating in restaurants. Waiters (and sometimes kitchen staff) may not always know the ingredients of every dish. Depending on your sensitivity, just walking into a kitchen or restaurant can trigger a reaction.
Consider using a “chef card” to identify your allergy and what you cannot eat. Always inform 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 which dishes on the menu are safe.
Recognizing and Treating Anaphylaxis
Symptoms caused by a food allergy can range from mild to life-threatening, and the severity of each reaction is unpredictable. Even those who have previously experienced only mild symptoms may suddenly experience anaphylaxis, a life-threatening reaction that can impair breathing and cause a sudden drop in blood pressure. 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, resulting from exposure to an allergen triggering a flood of chemicals that can send your body into shock. Anaphylaxis can occur within seconds or minutes of exposure, worsen quickly, and be fatal.
Once diagnosed with a food allergy, your allergist should prescribe an epinephrine auto-injector and teach you how to use it. You should also receive a written treatment plan describing prescribed medications and when to use them. Regularly check the auto-injector’s expiration date and ask your pharmacy about reminder services for prescription renewals.
Anyone with a food allergy should always have two doses of their auto-injector readily available, as severe reactions can recur in about 20% of individuals.
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. Call for an ambulance (or have someone do so) and inform the dispatcher that epinephrine was administered and more may be needed. Go to the emergency room for monitoring.
If uncertain whether a reaction warrants epinephrine, use it immediately; the benefits outweigh the risk of unnecessary use.
Common side effects of epinephrine may include anxiety, restlessness, dizziness, and shakiness. In 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. Still, epinephrine is considered very safe and is the most effective medicine for treating severe allergic reactions.
Protecting Children with Food Allergies
No parent wants to see their child suffer. Fatal and near-fatal food allergy reactions can occur at school or other places outside the home, so parents of children with food allergies must ensure the 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 like sporting events and field trips. Ensure that you and those responsible for supervising your child understand how to use the auto-injector if one has been prescribed.
Conclusion
Managing food allergies requires vigilance, education, and preparedness. Understanding the most common allergens, recognizing cross-reactivity patterns, and knowing how to respond to allergic reactions can significantly improve the quality of life for individuals with food allergies and their families. Early diagnosis and careful management are key to preventing severe reactions and ensuring a safe and healthy life.
