Coronavirus Covid-19 Information

Frequently Asked Questions about Allergy

  • An allergy is an abnormal immune reaction to an otherwise harmless environmental substance.

    1. Inhalants – Grass and tree pollen, house dust mite, animal dander and moulds
    2. Medications – for example antibiotics
    3. Foods – the big 8 listed below:
    • Egg 
    • Cow’s milk
    • Wheat
    • Soy
    • Peanut
    • Tree nut
    • Fish
    • Shellfish

    Other foods account for <10% of food allergies. Allergies to fruits do seem to be becoming more common, especially in adults but are thankfully usually mild.

  • The most important step in making an allergy diagnosis is taking the patient's 'clinical history'. This is where a doctor will examine the details of the circumstances around a reaction and try to relate the symptoms experienced to the history of exposure. The doctor will often then arrange tests that will help to clarify the clinical history. Testing approaches that are used include:

    • Skin prick testing
    • Blood testing (Specific IgE testing; carried out in the immunology laboratory)
    • Challenge testing

    It is important to understand that allergies cannot be diagnosed by testing alone. Testing identifies a state known as 'sensitisation' that might suggest an increased risk of clinical allergy – however, for doctors, the clinical history is the most important step in making a diagnosis. The only way to absolutely prove an allergy is a challenge test – this is a supervised exposure to the substance in question. The development of allergic symptoms during a challenge, confirms the diagnosis.

    In St James’s Hospital all three testing approaches are used. Challenge testing is time consuming and has some risk. Waiting times for challenge tests are currently very long.

  • A food allergy is an acute (rapid onset) reaction, involving the immune system. A food allergy occurs reproducibly after exposure to a food and does not occur when that food is avoided. Symptoms are often mild but can occasionally be life threatening (anaphylaxis).

    Food intolerance reactions are usually of slower onset and do not cause life threatening reactions. Intolerances frequently cause digestive problems (for example bloating, pain, or diarrhoea) only, but these may be debilitating and have a huge impact on quality of life. Absolute food avoidance is often not required and implicated foods may be tolerated in small amounts or in different forms (eg. white bread v's wholemeal bread). Lifestyle changes can also help intolerances. This might include modifying caffeine and alcohol intake, abdominal muscle strengthening exercises and also relaxation and mindfulness.

  • There are no definitive, validated (proven) tests to diagnose food intolerances. The best approach is to ask for an assessment with your GP. Your GP will seek to make sure there is nothing else going on and may arrange tests to make sure you do not have coeliac disease (a very specific form of gluten hypersensitivity), or camera tests to examine the gut further.

    If food intolerance is felt to be the cause, then the best approach is to use a food diary to relate symptoms to food groups. If the diet is to be modified this should be carried out one food at a time and for a period of 4-6 weeks to see if exclusion is effective. This is best done with the help of an experienced dietician. In some cases, more general dietary modification might be of benefit such as adherence to a specialised diet. For example the low FODMAP (Fermentable Oligo-, Di-, Monosaccharides and Polyols) diet. Again, the involvement of an experienced dietician is crucial.

  • There are no evidence based, validated tests for food intolerance.

    Food specific IgG testing is commonly marketed in pharmacies and other commercial outlets. This test detects a normal (physiological) response to food. Positive tests reflect dietary exposure only and do not identify any disease process. Other tests such as kinesiology, VEGA testing, hair analysis etc. are not scientifically based and lack supportive evidence, or have been disproven. In addition, practitioners offering these tests may confuse allergy and intolerance resulting in risk for patients. This does not mean that dietary modification in the setting of food intolerance is wrong, it merely means that the tests that are proposed to diagnose intolerance, are unhelpful. There is ample evidence that these tests are unable to differentiate patients with intolerance symptoms from those that do not have such symptoms.

    Such tests are an expensive waste of money and time. These testing strategies are not available in St James’s Hospital.