Adult-onset food allergy (Adult – Onset Food Allergy) is not far-fetched and can occur. Sometimes foods you used to eat without any reaction may now—or in the future—trigger a food allergy. Severity ranges from mild to severe. Being aware and responding correctly helps prevent unexpected severe reactions.
What is adult-onset food allergy (Adult – Onset Food Allergy)
Adult-onset food allergy (Adult – Onset Food Allergy) is an acute allergic reaction caused by an abnormal immune response that misidentifies substances that were previously harmless to the body. Symptoms usually occur within minutes after eating the triggering food or within 2 – 4 hours. Symptoms may include itchy rashes on the body, swollen lips, facial swelling, or other system involvement. It is commonly found with seafood, tree nuts, and fresh vegetables and fruits.
The main contributing factors involve changes in the gut immune system due to environmental changes, stress, chronic illness, aging, changes in gut microbiome balance, antibiotic use, or gastrointestinal diseases. These make the body more prone to developing allergies to foods that previously caused no symptoms.
Co-triggers that make food allergy more likely (Cofactors)
Some patients may be able to eat a given food without symptoms, but may develop an allergic reaction when cofactors are present as follows:
- Exercise (Food – Dependent Exercise – Induced Urticaria/Anaphylaxis; FDEIA), e.g., wheat flour or seafood combined with exercise within 1 – 4 hours
- NSAIDs such as aspirin, which increase absorption of allergens in the gut
- Alcohol, which increases dispersion and absorption of allergens into the bloodstream
- Infection or illness, which makes the immune system more reactive
- Hormonal changes during menstruation
- Stress and insufficient rest
Warning signs of adult-onset food allergy (Signs and Symptoms)
- Skin: itchy rash, hives, swollen lips, swollen eyes, itching in the mouth, tongue, or throat
- Gastrointestinal system: nausea, severe vomiting, or immediate diarrhea
- Respiratory system: throat tightness, chest tightness, difficulty breathing, or wheezing
- Circulatory system: lightheadedness, dizziness due to low blood pressure
**If you develop hives all over the body, swelling of the lips, or symptoms involving 2 or more systems, go to the hospital immediately.**
Diagnosis of adult-onset food allergy (Diagnosis Procedure)
If you have symptoms of a food allergy, you should see a doctor promptly for food allergy testing. There are several methods including:
- Skin testing (Skin Prick Test) using real foods (Prick to Prick test) or standardized extracts (Allergen Extract) from suspected foods, placing drops on the skin and pricking with a needle to observe the skin response. This helps diagnose IgE-mediated food allergy (IgE – Mediated Food Allergy).
- Blood test for Specific IgE (Serum Specific IgE for food) to measure levels of IgE antibodies specific to proteins in each food type in serum. This helps diagnose IgE-mediated food allergy (IgE – Mediated Food Allergy).
- Oral food challenge (Oral Food Challenge Test), the gold standard for diagnosing food allergy, in which the patient eats small, gradually increasing amounts of the suspected food at specified doses and intervals under specialist supervision. It is used when skin testing or Specific IgE blood testing is inconclusive, to determine the amount a patient can eat at one time without symptoms and to test alternative foods.
Treatment and management for adult-onset food allergy (Treatment and Management)
Treatment and management of adult-onset food allergy focuses on preventing recurrent reactions, preparing for emergencies, and managing cofactors.
1) Main treatment approaches
- Strictly avoid suspected allergenic foods, the most important preventive method. Check ingredients every time before eating, beware of cross-contamination, and practice reading food labels carefully, looking for allergen names or warning statements such as “may contain…”
- Managing cofactors such as avoiding NSAIDs or alcohol together with suspected allergenic foods, and avoiding exercise for at least 2 – 4 hours both before and after meals if Food – Dependent Exercise – Induced Urticaria/Anaphylaxis (FDEIA) is suspected, etc.
- Always carry symptom-relief medication and emergency medication
- Second-generation oral antihistamines (Second – generation Oral Antihistamine) to relieve mild allergic symptoms such as itchy rashes, mouth itching, or localized hives, but they cannot prevent or treat severe allergic reactions (Anaphylaxis).
- Epinephrine auto-injector (Epinephrine Auto – Injector; Epipen) the only primary medication for treating anaphylaxis. It must be carried at all times by those with a history of severe reactions or high risk, under specialist guidance.
2) Additional recommendations
- Always carry a food allergy card (Food Allergy Card)
- Create an anaphylaxis action plan (Anaphylaxis Action Plan): a written emergency plan specifying symptoms requiring epinephrine, dosage, emergency contact numbers, and steps so that close contacts or bystanders can help immediately
- Inform restaurant staff or the chef about your food allergy every time you eat out: ask about food preparation steps to avoid cross-contamination with allergenic foods
- Eat a high-fiber, varied diet to support gut microbiome balance
- Keep a daily log of foods and ingredients consumed: if new allergic symptoms occur, this record helps identify associations between symptoms and foods, improving diagnostic accuracy
- Consult a specialist before broadly eliminating foods: do not avoid many foods solely based on Specific IgE blood test or Skin Prick Test results without a true history of reactions from eating those foods, to prevent nutritional deficiencies and unnecessary loss of quality of life
What is cross-reactivity (Cross – Reactivity)
Cross-reactivity (Cross – Reactivity) is a condition in which an allergy to one food or allergen leads to allergic symptoms to another food with a similar protein structure or properties, even if the latter has never caused an allergy before. Common examples include shellfish, latex-containing fruits, and certain nuts—for example, shrimp allergy may be followed by reactions to crab or crayfish; or latex allergy may cause reactions to banana, avocado, kiwi, etc.
Oral Allergy Syndrome; OAS (Pollen – Food Allergy Syndrome; PFAS) is a food allergy caused by cross-reactivity between pollen-specific allergens (Pollen) and similarly structured proteins in certain vegetables, fruits, or nuts. For example, if allergic to birch pollen, symptoms may occur when eating apple, peach, plum, pear, hazelnut, or carrot because the immune system mistakenly recognizes them as pollen due to similar protein structures, triggering an allergic reaction.
Can food additives cause allergic reactions?
Many foods contain additives (Food Addictives) to extend shelf life, add color, or adjust taste, such as preservatives, food coloring, monosodium glutamate, and flavor enhancers. In some people, these substances may trigger an immune response in a non–IgE-mediated food allergy (Non – IgE Mediated Food Allergy). Although symptoms may resemble typical food allergy such as hives, flushing, or lip swelling, symptoms are usually not severe.
When should you suspect an allergy to food additives?
- Symptoms relate to the amount consumed: a small amount may not cause symptoms, but a larger amount can trigger symptoms.
- Symptoms occur only sometimes after eating, even with the same type of food.
- Symptoms occur with multiple unrelated foods, such as dried shrimp, wine, and dried baked vegetables, that share sulfites as a common ingredient.
The main diagnosis is an oral food challenge test (Oral Food Challenge Test) under a physician’s guidance, along with avoiding dietary sources that trigger symptoms.
Why are modern people experiencing more food allergies?
Most of the body’s immune system is related to the gut, and microorganisms in the gut—or the gut microbiome—help maintain immune balance. When the microbiome balance is disrupted by factors such as unnecessary antibiotic use, regular consumption of processed foods, accumulated stress, and inadequate sleep, beneficial microbes decrease. This leads to immune dysfunction and the development of allergies.
If you suspect a food allergy, should you eliminate foods?
If you suspect a food allergy, you should see a specialist as soon as possible for Skin Prick Test, a Specific IgE blood test specific to that food, or an oral food challenge test (Oral Food Challenge Test) to clearly determine whether it is a true food allergy. You should not eliminate foods on your own without clear test results, as this may lead to nutritional deficiencies and avoiding the wrong foods, to enable appropriate care and guidance going forward.
Which hospital specializes in treating food allergies?
The Allergy and Asthma Center, Bangkok Hospital is ready to provide assessment, diagnosis, and close care for patients with food allergy symptoms, as well as counseling and accurate information, with a team of specialist physicians and a multidisciplinary team with expertise and extensive experience to help patients maintain a good quality of life.
Physician specializing in food allergy treatment
Dr. Chawisa Panaphorn, specialist in allergy and immunology, Allergy and Asthma Center, Bangkok Hospital
You can click here to make an appointment yourself.
