A. Case study
B. More information
C. Editors' comments
D. References
E. CPD questions (South Africa, Australia



A. Case study
A 35-year-old male visited his dietitian after experiencing periodic episodes of urticaria. They had occurred for 1½ - 2 years, the frequency varying from once a week to once in a couple of weeks. The patient would wake up in the early hours of the morning with slight difficulty in breathing. He would then notice urticaria all over his body. He also mentioned 2 or 3 episodes of these symptoms late in the evening before retiring for the night. Because the reactions did not interfere with his well being excessively, he was not greatly concerned. But after one episode that was more severe (his throat started to close up), he decided to get to the root of the problem.

What can cause urticaria? There are many causes:
1. Physical stimuli: By questioning the patient, the following types of urticaria were excluded: cholinergic, cold-induced, delayed-pressure, solar, vibratory and aquagenic urticaria, as well as dermatographism.

2. Contact sensitivity: The patient was asked whether he had ever noticed any symptoms after coming into contact with an item, including in his occupation. He was not sure, but did not think so. A contact sensitivity is, however, unlikely, as one would expect a localized reaction on contact and not such a generalized reaction over the body.

3. Hypersensitivity to insect stings or bites: Because the reaction occurred quite frequently, this was excluded as a possible cause.

4. Hypersensitivity to a drug: He was questioned about his use of pharmaceuticals, including over-the-counter medications, vitamins, "naturopathic" supplements and other herbal remedies, but no correlation could be determined.

5. Hypersensitivity to a food or food additive: The patient was asked whether he had ever noticed an association between food ingestion and the appearance of symptoms. He could think only of chicken. He had been avoiding chicken since early childhood, as he was prone to "tight chest" from eating this food, and serum-specific IgE to chicken had been increased. He was questioned about other foods that might contain chicken, but he was not aware of eating any of them.

6. Because he experienced the symptoms only in his house, environmental allergens (e.g., house dust mite, fungi, pollen, trees, pets, etc.) needed to be considered, though it is uncommon for them to cause symptoms such as his. But the symptoms occurred only infrequently and irregularly, so these causes were very unlikely.

7. Collagen vascular disease, chronic idiopathic/auto-immune urticaria (e.g., autoimmune thyroiditis, vitiligo, alopecia areata, pernicious anemia and colitis) and infectious diseases (although controversial) may also cause urticaria, but these last resorts for an inquiry will not be discussed here.

What is the next step in investigating for a food or food additive sensitivity?
1. Food-symptom diary
2. Skin prick tests or blood tests
3. Elimination diet and food challenges

1. Asking the patient to keep a food-symptom diary could help to identify the culprit food(s).

2. Skin prick tests and blood tests would not be relevant if the patient were sensitive to an additive, but only if it was IgE-mediated. If the results show that the total IgE level is increased, the patient has an underlying allergy-in this case either still to chicken or to a new allergen. If the tests are negative, it does not rule out an allergy. It can be a non-IgE-mediated reaction. Because there is little indication as to what food might be causing the symptoms, the decision to do skin prick or serum-specific IgE-tests would entail testing for a wide range of foods. It would thus be an expensive and possibly fruitless exercise.

3. If the culprit foods cannot be identified by the food-symptom diary, an elimination diet with oral challenges would be the next step.

The patient was asked to keep a detailed food-symptom diary until he experienced 2 episodes of adverse reactions. After the second episode occurred, the dietitian analyzed the food diary. Both times, the patient had been eating sausage. After further interrogation, it was determined that he had changed butchers almost 2 years ago and had been buying sausage only from the new one since then. The patient had been eating sausage before that date without any adverse effects. Through questioning the butcher about the ingredients, it was determined that he puts chicken (which is an unusual sausage ingredient) in the sausage. The patient and his friends had barbecues quite regularly (once a week to once in a couple of weeks), during which he would usually eat sausage. This normally occurred in the evening (which would cause the reaction in the early morning hours), but sometimes in the afternoons (which would cause the reaction before bedtime). It was thus determined that the adverse reactions that he had been experiencing was due to a hidden allergen (chicken) in sausage.

TIP for Allergy Advisor users:
Allergy Advisor has useful features to assist users with determining Hidden allergens in foods. Clicking the "Hidden Allergens" button on the "Management" menu, presents the user with lists of uncommon terms on food labels that may indicate one of the major allergens. Hidden allergens are also listed on the diet sheets printouts for patients, also accessed from the "Management" menu. Searching for an allergen using the "Items, substances & allergens" button on the Main menu, may also indicate the presence of a Hidden allergen in the "Possible additional constituents" window, e.g., the presence of anchovy in Worcestershire sauce (used in some recipes).

B. More information
Hidden allergens are present in products without the normal consumer being aware. The product is contaminated with the allergen during manufacturing, either on purpose, to fulfil a specific function, or by accident.

Adverse reactions can occur in different degrees of severity: from a hardly noticeable reaction, to anaphylaxis or death. A reaction can be induced by the ingestion of only minute quantities of food allergens or even by inhalation of dust or cooking fumes. In the most vulnerable individuals, extreme caution should be taken. But any allergic patient should be familiar with all the foods that can contain the relevant allergens, as well as the terms used in the labelling of products to describe the allergen. Many anaphylactic reactions have been caused by exposure to hidden allergens, especially when eating away from home. Because of the almost unlimited uses of soy, for example, it is a particularly insidious hidden allergen. Soy is so widely distributed in processed foods that avoidance of soy in the diet is very difficult.1 Therefore, thorough education on avoiding this type of allergen is essential.

This newsletter will focus on the ways that allergens are used and/or disguised in the manufacturing and labelling of processed foods.

Causes of allergens being hidden in foods

  • Contamination of a safe food:
    • When a manufacturing plant uses the same equipment to make different products without adequate cleaning of the equipment. Examples are the manufacturing of ice cream and milk-free sorbet with the same equipment; and chocolate products made in a factory that also produces peanut-containing snacks. The same can occur when the same oil is used for cooking fries and fish in a fast-food outlet.
    • When manufacturers use already manufactured products for the manufacture of a secondary product, e.g., mayonnaise used in the manufacture of a salad dressing. This may not prompt the listing of egg, particularly if this ingredient is less than a certain percentage of all the ingredients in the new product. This percentage varies between countries, but most use a standard of <5%.
    • When allergens such as cockroach and storage mite contaminate a product during storage and transport.
    • When deli meat slicers are not properly cleaned between slicing of different products, e.g., both cheese and meat.

    • When the same serving utensils are used for different foods (e.g., in salad bars and ice cream parlors) and not properly cleaned in between.

    • When contact occurs through the handling of food, e.g., contamination of lettuce with latex allergen by staff wearing latex gloves.1

  • Crude edible plant oils generally contain allergen proteins, which could induce allergic reactions. Refined, heated oils, however, are usually not allergenic, but reactions have been recorded. The allergenicity of the oil would generally depend on its purity, which in turn depends on the extraction process.2
  • Manufacturers may change ingredients without indicating this on the label, as when a shortage of vegetable oil results in substitution with a tropical oil.
  • Because legislation may permit a manufacturer not to list an ingredient constituting less than a specific percentage of the total product (<5% in most countries), noodles for example containing egg may not have egg listed on the ingredient panel. A similar situation may occur when egg white is used to give pretzels, bagels, and other baked goods their shiny appearance. Peanut butter may also be used to "glue down" the ends of egg rolls.
  • In processed food, ingredients can be added for a specific application, for example as a binder, coagulant, protein extender, or emulsifier. The ingredients are usually listed on the ingredient panel by these terms alone, and not their common names. The only way to identify the substances specifically is to contact the manufacturer. Examples are egg that can be used as a binder, protein, or emulsifier; and natural flavors such as pineapple, milk casein, or hydrolyzed soy protein, which may be used and listed as flavoring or natural flavoring, as in microwave popcorn. Laws that govern this have been changed, but not throughout the world.

  • Misleading labels may disguise hidden allergens. An example of this is "non-dairy" creamers or coffee whiteners that contain skim milk; and meat products that contain soy. Some margarine, claiming to consist of 100% corn oil, may in fact contain skim milk powder. A drink advertised for "people who cannot drink milk" is in actual fact milk with lactase enzyme and meant for individuals with lactose intolerance, but it clearly still contains milk protein. Peanuts can be "deflavored," "reflavored," and pressed into other shapes such as those of almonds and walnuts. These products retain the allergenicity of the peanut.
  • Mistakes take place when consumers assume that a brand of food that uses similar labels for a range of products has similar formulations.
  • A food may be listed on the product label by an uncommon term, for example the term casein is not recognised by consumers as an indication of cow's milk.

  • In addition to food products that may be dangerous to sensitive individuals, allergens are also found in cosmetics (e.g., peanut), shampoos (e.g. egg), and pharmaceuticals. More and more pharmaceutical companies are using natural ingredients in their products. It is thus more likely that food allergens are present in the latest pharmaceutical products.
  • Allergens can be transferred through non-food products. For example, adverse reactions have been recorded from exposure to peanut while playing cards, touching other children's toys, kissing, etc.
  • Allergens may be "hidden" in an environment as well. Adverse reactions have been recorded from inhalation of peanut in-flight and inhalation of fish allergen upon entering a restaurant that serves fish.1

Prevention is better than cure

  • Allergic persons and/or their caretakers should educate themselves about the specific allergies in question. They should know all possible sources of exposure, including hidden allergens.

  • Allergic persons and/or their caretakers should scrutinize food labels at all times and contact manufacturers if they are unsure about an ingredient.

  • Individuals with severe food hypersensitivity should probably avoid processed foods. If it is necessary to purchase these foods, they should come from a reliable manufacturer.

  • Children should be taught to manage their allergies from an early age, so that it becomes a way of life and they don't think that they are different or abnormal.

  • Teachers should be educated to prevent exposure to pertinent allergens. This includes making sure that the susceptible child does not share any toys or food with children who have had exposure to the allergens in question.

  • Remember that "natural" does not mean that the product is safe.

  • Remember there are no 100% hypoallergenic foods.

  • Extensively hydrolysed formula can induce symptoms in 10% of milk-allergic children. If possible, hypoallergenic formulas should be tested in each case before being prescribed for children sensitive to cow's milk.

  • The very sensitive individual should wear a Medic Alert bracelet and carry an epinephrine (adrenaline) self-injector at all times.

  • Less sensitive individuals may need to carry antihistamines with them.

  • Many individuals lose their reactivity to foods over time, some completely and others only partially. Careful and periodic challenges with the allergen can be done to save families from prolonged anxiety about accidental exposure. It is imperative that the CAP RAST level be measured before the challenge in highly allergic individuals. If the level is increased, the challenge should be postponed.

  • To make the lives of highly allergic individuals easier, food manufacturers should aim to bring common ingredient names into use and to be consistent with the names and ingredients that they use. Also, legislation should be stricter, forcing companies to make their food labels more accurate. It is, for example, necessary to label the source of the additive. The recommendation was made to Codex Alimentarius to list the derivative in brackets after the ingredient, for example, ovomucoid [egg], but not all governments have implemented this yet.1

  • Steinman1 discusses specific hidden allergens (egg, milk, soy, wheat, peanut and fish) in detail and lists the terms that may appear in food labels. This comprehensive article is available at

    compiled by Karen du Plessis B.Sc. Diet.
    Food & Allergy Consulting & Testing Services (FACTS)
    PO Box 565
    Milnerton 7435
    South Africa

    C. Comments by our editors

    Prof Janice M. Joneja Ph. D., RDN
    The case study is a very good example of the identification of a hidden food allergen, however, in many cases of adverse reactions to food components, the culprit is not so easy to detect. This is particularly true when non-immunologically-mediated intolerance is the cause of the reaction. Urticaria, throat tightening and nasal congestion, as cited as symptoms in this case study, can be caused by an intolerance of histamine without the mediation of an allergen-triggered immune response. In this situation, the reaction is due to the deficiency of an enzyme, probably diamine oxidase, which breaks down excess histamine in the body. Symptoms occur when histamine reaches a critical level. Histamine is present in many foods, particularly those that are fermented by micro-organisms as part of the manufacturing process (for example, cheeses, wines and other alcoholic beverages, processed sausages, soy sauce, sauerkraut). Symptoms appear apparently haphazardly because it is the total level of histamine that is important, not the presence of a specific food allergen, and the level will fluctuate in response to both intrinsic and extrinsic sources of the amine. When histamine intolerance is the cause, symptoms can usually be controlled with a histamine-restricted diet. Histamine intolerance is suggested when food allergy has been ruled out, and is confirmed by elimination and challenge of histamine-rich foods. {Reference: Joneja JMV and Carmon Silva C. Outcome of a histamine-restricted diet based on chart audit. Journal of Nutritional and Environmental Medicine 2001 11(4):249-262}

    Dr. Harris Steinman M.B.Ch.B.
    This case report draws very nicely attention to the problem of hidden allergens, which can contribute to the exacerbation of symptoms in allergic individuals. Severely allergic individuals who are at risk for anaphylaxis are a particularly important subset of this group. It is thus imperative that doctors refer food-allergic individuals to dietitians for thorough counselling, and for dietitians to be familiar with ingredients of common products, the use of uncommon terms for some of the additives used in these products that are derived from major allergens, and to be familiar with labelling laws.

    For more information on this subject and other allergy and intolerance related topics, visit:

    To join a professional food allergy discussion list where this subject can be discussed further, go to or

    We invite you to send us interesting case studies. We pay US$100 for each case study we use in our newsletter.

    To subscribe or unsubscribe, send an e-mail to and put "subscribe" or "unsubscribe" as the subject.

    D. References
    1. Steinman HA. Hidden allergens in foods. Journal of Allergy and Clinical Immunology 1996;98(2):241-250.
    2. Besler M, Steinhart H, Paschke A. Stability of food allergens and allergenicity of processed foods. J Chromatogr B Biomed Sci Appl 2001 May 25;756(1-2):207-28.

    E. CPD Questions (South Africa, Australia)

    This CPD session is now closed. Please contact for more information.

    1. True or false: Contamination of a safe food can occur when a manufacturing plant uses the same equipment to make different products without adequate cleaning of the equipment.
    (a.) True
    (b.) False

    2. Which of the following is not true regarding hidden allergens in oils?
    (a.) A safe food can be contaminated when the same oil is used for cooking different products.
    (c.) Crude edible plant oils can contain allergen proteins.
    (d.) Refined, heated oils can contain allergen proteins.
    (e.) Oils never contain allergenic proteins.

    3. True or false: If any food were present in a quantity of less than 5% of the total product, it would be safe to eat.
    (a.) True
    (b.) False

    4. Which of the following products can contain food allergens?
    (a.) Cosmetics
    (b.) Shampoos
    (c.) Pharmaceuticals
    (d.) All of the above

    5. True or false: Allergens have been transferred through contact with non-food substances: for example, during playing cards, touching other children's toys and kissing.
    (a.) True
    (b.) False

    6. Which of the following should a highly allergic individual not do?
    (a.) Learn everything possible about the allergy.
    (b.) Scrutinize food labels at all times.
    (c.) When unsure about the contents of a product, try a small piece.
    (d.) Make sure that a processed product is from a reliable manufacturer before eating it.

    7. Which of the following is good advice in the case of a highly allergic individual?
    (a.) Scrutinize all labels unless it says that the product is "natural".
    (b.) If there is a choice, go for the "hypoallergenic" option.
    (c.) Without exception, milk-allergic infants should use an extensively hydrolysed formula.
    (f.) Wear a Medic Alert bracelet and carry an epinephrine (adrenaline) self-injector at all times.

    8. True or false: Highly allergic individuals need not do any tests before they start challenging themselves with the foods that they are allergic to.
    (a.) True
    (b.) False


    1. a [X] b [ ]   2. a [ ] b [ ]c [ ] d [X]   3. a [ ] b [X]
    4. a [ ] b [ ] c [ ] d [X]   5. a [X] b [ ]   6. a [ ] b [ ] c [X] d [ ]
    7. a [ ] b [ ] c [ ] d [X]   8. a [ ] b [X]    

    1. a. True
    2. d. Oils never contain allergenic proteins.
    3. b. False
    4. d. All of the above
    5. a. True
    6. c. When unsure about the contents of a product, try a small piece
    7. d. Wear a Medic Alert bracelet and carry an epinephrine (adrenaline) self-injector at all times.
    8. b. False