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Dr Harris Steinman 

The purpose of this talk is to enlighten you to the potential adverse effects that allergens can have on the health of individuals and communities. The field of allergy is still relatively new and our knowledge is expanding at a rapid rate. Also, the prevalence of allergy is increasing and about 25%-35% of population will develop some form of allergy over their lives. This talk will focus mainly on food allergy and allergens and not asthma, eczema, hay fever and the other allergic conditions. It is important to recognize that many of these conditions are intertwined. Although this talk cannot hope to cover all the important details in the time allocated, the most important themes will be addressed. 


Much  confusion has been generated by a misunderstanding of the various types of adverse reactions one can experience to food. 

Adverse reactions to foods can be broadly categorized in three groups: Non-toxic reactions, toxic reactions, and psychological mechanisms. 

A. Psychological

These include food aversion, food fads where health is affected, or mental disease such as schizophrenia.


B. Toxic

This is a reaction to a food containing naturally occurring toxins. Examples include poisonous mushrooms, lectins in beans, or toxins that develop when food is contaminated by bacteria or moulds (aflatoxins).


C. Non-toxic

Although this group is termed “ non-toxic”, death can result from adverse reactions in this group. Causes for the majority of adverse reactions to food will be found in this group, and are classified into two large subgroup: Immune mediated ( allergy) and non-immune mediated ( intolerance).


I n allergy, the basic mechanism is that the body sees the food as a foreign protein and mounts a reaction against it. This reaction usually involves the body’s immune system. Reactions due to an intolerance mechanism occur when the body does not have enough of a chemical to break down a component of the food, the food has excess of the component, or the food contains a substance that has a drug-like action, for example caffeine.


In the former, any amount may result in an adverse effect. In the latter, the reaction is usually dose dependant.


Who gets food allergy?


Although there is a higher risk of developing an allergy if your parents had an allergic condition, in fact any individual can develop allergy at any stage of their life. Food allergy is predominantly a disease of children the majority outgrow the allergy. This will be discussed later on. It is also a fact that allergic have increased over 300% in the last 15 years. At that stage about 5% of the population was known to have an allergic condition. Among black population allergy affected less than 1% 15 years ago. A recent study conducted in the Transkei showed that over 34% were sensitized to 1 or more allergens in the environment.


Causes for the increasing prevalence of food allergy


Scientist are not absolutely clear on the exact mechanism responsible for the increasing prevalence of food allergy but there are some very clear factors involved. Smoking, early weaning into solids, and non-breastfeeding practices have been clearly implicated as risk factors. Western style home environment (decreased ventilation, carpets, bedding), additives and preservatives, and pollution has also contributed to the increase.




Allergy reactions can be mild to life threatening. In the USA, more individuals die due to an allergic reaction to food than to bee sting. Reactions may cause nausea, vomiting and diarrhoea, involve the mouth and throat alone, result in exacerbation of asthma or hay fever, or be life threatening with airway constriction of shock and collapse. We have recently become aware of individuals who only develop symptoms following ingestion of a food to which they are allergic to, but only accompanied by exercise or work within three hours following ingestion of the offending food.


What are allergens?


In general, these are proteins. All foods contains variable amounts of protein. These may be recognized by the body as foreign, resulting in the body mounting an immune response against that protein. However, in certain instances, for example penicillin, the substance contains no protein, but binds with a protein and form hapten that is recognized by the body to be foreign. In general, although an individual can react to any food, 95% of reactions experienced occur due to allergy to egg, milk, peanut, wheat, Soya and fish. In general, allergic individuals are seldom allergic to only one food but typically to two or more. 

Heat lability and stability 

The majority of allergens are heat-labile, that is, they are destroyed or denatured by heat. This is not the case in those listed above. For this reason, they have the potential to exert their allergenic effects even when a manufactured product containing one of these foods as an ingredient is ingested. Generally, all food contains more than one protein; milk contains the major proteins casein and whey as well as other minor proteins, and individuals usually are allergic to more than one protein in a particular food. In certain instances, these proteins may be heat labile and heat stable. Thus some children will be allergic to both fresh and boiled milk if allergic to casein, whereas those allergic to milk but not the casein component may tolerate boiled milk. The whey protein is denatured with heat.


Amount required for reaction


 Individuals who are highly allergic may react to less than 10 mg of an allergen. We have seen children reacting to even less; touching a counter that had been in contact with raw egg. This is a very important consideration in food service areas where utensils may inadvertently be used for serving more than one food. For example, accidental contamination of meat with milk or cheese may occur at deli counters, sorbet with milk from ice –cream and contamination of ordinary ice cream with ice cream containing nuts. As the food manufacturing industry strives to replace artificial additives with natural additives, allergic individuals are at risk of adverse reactions from the residual protein of the parent food, for example severe egg-allergic reactions due to lysozyme from egg being used as a preservative, or adverse reaction to soya-derived emulsifiers.


Influence of ripeness


To further complicate the diagnosis of food allergy, it is evident that the degree of allergenicity of certain foods such as tomato and tree nuts change according to the ripeness




There is an increased risk that individuals allergic to a food may be allergic to other foods from the same family. The importance of this varies from food family to food family. Recently we have become aware of cross-reactivity not involving plant families. Individuals allergic to Birch pollen are very likely to be allergic to apple. Latex-allergic individuals are at higher risk for being allergic to avocado, kiwi fruit, mango and chestnut. 

Environmental concerns 

There are some instances where allergens are not localized to individual homes or controlled environments resulting in a higher risk of exposure to allergic individuals. Barcelona experienced a massive surge in urgent hospitalization for individuals with asthma when soya beans were being unloaded from the local port and soya dust drifted across the city. Occupational allergens may result in an increased prevalence of particular allergies. Bakers are more likely to be allergic to wheat and enzymes such as amylase. Allergic children are at higher risk for accidental ingestion of allergenic food at school and other areas of group activity. Cooking fish results in  vaporization of  the protein particles and severe reactions have been recorded in allergic individuals who inhaled these fumes. 

Hidden allergens 

It is particularly important for children and adolescents to be aware of hidden allergens in foods. These young people are especially vulnerable to commercially prepared foods which are the foods most likely to contain hidden allergens. It is therefore important for food sensitive person to read and understand food labels. Unfortunately some labels are inaccurate, misleading or incomplete. It is thus important that persons at risks are able to manage any severe reaction to a hidden food allergen.


Hidden allergen                                           Food


peanut                                                           peanut butter, peanut oil, pastry, candy, nut                                                                           

                                                                      mix, cereals


milk                                                              sorbet, Cremora, margarine, sausages.


Soya beans                                                   hamburgers, mince meat, hot chocolate, milk



Cereals                                                         snack foods, processed meats, ice cream, soup



Egg                                                               pasta, meatballs, macaroni, lemon curd,  


Casein                                                           butter substitute, sausage, canned fish, candy,



Yeast                                                             bakery products, beer, mayonnaise, ketchup


Antibiotics                                                     cows milk, beef, pork




Emerging allergens


Not only is the prevalence of allergy increasing but new allergens are making their appearance. Before the AIDS crisis, latex allergy was unknown. With increased need for latex gloves and condoms, manufacturers decreased washing of these products  resulting in increased protein residue, which has resulted in increased sensitization in health professionals and the general public. Analysis of donor blood shows that 6% of individuals contain specific antibodies to latex. More than 12% of health professionals either have had to change their specific profession or take special precaution to avoid latex. The crisis we are experiencing can be put into context if one considers latex’s cross-reactivity with various foods, that latex can contaminate food from transfer of latex particles from gloves, and that many other common day items are made from latex, e.g. Pacifiers, tyres, it should be clear that we may be confronted with a major health disaster.


Recent studies have shown cockroach to be a major allergen risk, with 20-40% of allergic individuals being allergic to this allergen. A major route of exposure to these allergens has now been shown to be the cockroach allergen present in flour, stored food, and wheat and other grains,


Food from Genetically Modified Organism (GMO) has the potential to affect health by introducing a known allergen from one plant to another. This was demonstrated when Brazil nut protein was introduced to soya bean in attempt to increase the methionine levels in the later. Individuals allergic to Brazil nut would have experienced allergic reactions upon eating this soya bean hybrid. There is also concern that GMO food may inadvertently result in a novel protein that may be allergenic. We need to also recall that adverse reactions to food are not only allergic in nature, but that foods are “ chemical warehouses” containing other substances such as histamine and tyramine, which may affect health.


What happens with allergy over time 


Children allergic to the so-called potent allergens, peanut and egg, will probably remain allergic to these forever. Children allergic to cow’s milk usually outgrow this allergy within a year, whereas allergy to fish and wheat may take longer. Adults who develop a food allergy will tend to retain their allergy.




Allergens are a potential environmental  health hazard. It is crucial that all individuals involved in environmental health be sensitized to these potential health risks.
















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