Approximately 4 to 8% of children and 1 to 2% of adults have a true food allergy.
True food allergies are an atypical immunological response to the ingestion of the offending food. Virtually all known food allergens are proteins, and an individual must first be sensitised by exposure to the protein to develop antibodies, which then react to further exposures.
Food allergies need to be distinguished from food intolerances, which are generally caused by chemical agents, e.g. sulphites, or certain genetic deficiencies, e.g. lactose intolerance.
There are two stages in the development of an allergy, and the first is called sensitisation. This process happens when an allergen is encountered by the immune system and antibodies are made against it, despite it being harmless.
After sensitisation, the immune system retains a memory of the allergen and will recognise it if it meets it again. You do not always become sensitised the first time that your body encounters a particular allergen – a substance may be tolerated for many years before an allergy develops.
Sensitisation can happen in utero and can also occur through breastfeeding.
Once you have been sensitised, even a tiny quantity of that allergen can lead to an allergic reaction. When ingested, the allergen binds to the IgE antibodies present on the surface of the mast cells and basophils, leading to the release of toxic granules. If this reaction were the result of a parasitic infection, these chemicals would help to kill and digest the invading organisms.
If, however, the immune system is reacting against a harmless allergen such as peanut protein, these substances serve no useful purpose, but instead cause an increase in the blood supply to the tissues, leakage of fluid from the small blood vessels and local irritation.
The result is hotness, redness, itching and swelling in the affected area, and the production of excess watery secretions. In addition, the muscles of the airways in the lungs and the bowel may go into spasm, causing wheezing, shortness of breath, abdominal colic and diarrhoea. This process gives us the symptoms that we associate with allergy.
Allergy sensitivity is different for various individuals; different symptoms may be displayed after eating the same food product, and the symptoms exhibited may depend on the amount ingested. Some allergic consumers can tolerate a certain amount of the substance they are sensitive to, whereas others may have a seemingly zero tolerance.
When a person has an allergic reaction, the symptoms can be displayed in a number of ways. An individual may exhibit several different symptoms, or just one. The symptoms will differ in severity for each individual, and the symptoms may also depend on the various exposure circumstances e.g. what was eaten, how much allergen was consumed, whether the individual has done exercise, their state of health etc.
Symptoms can include problems with:
- The respiratory tract – rhinitis, asthma, throat swelling, (asthma is a rare response to food allergens)
- The gastrointestinal tract – nausea, vomiting, diarrhoea, abdominal cramping
- The skin – hives, itching, dermatitis, eczema
- Anaphylaxis – By far the most severe allergic reaction is anaphylaxis, which can happen at the time the food is eaten, or some time later. Individuals prone to anaphylaxis need to carry a shot of adrenaline with them at all times in case they accidentally consume the product they are allergic to. There is evidence to show that the severity of a reaction can be reduced and therefore the survival rate of anaphylactics increased by treatment with adrenaline within the first few minutes of an anaphylactic reaction.
The symptoms of anaphylaxis are a dramatic lowering of blood pressure, swelling of the tongue, lips and throat , restricting breathing, a generalised shock reaction, and ultimately possible death by multiple organ failure.
What are people most allergic to?
There is a group of 9 food or food groups [peanuts; tree nuts; soy; milk; egg; wheat; seafood (crustaceans, fish, and molluscs); sesame; and lupin] that cause about 90% of all allergic reactions, with hundreds of substances responsible for causing the other 10%. Basically, any food product that contains protein has the capacity to cause an allergic reaction in a person who has become sensitised to that protein.
Living with an allergy, either yourself or someone in your family, requires great compromise to the quality of life. It takes longer to find products in the supermarket that are safe to eat because of the need to study food labels and scrutinise ingredient lists, and it costs more because generally cheaper products and house branded foods have ‘may contain’-like allergen statements on the label.
The only way to guarantee freedom from an allergic reaction is to avoid the offending foods all the time.