What is allergy

An allergy is the response of the body's immune system to normally harmless substances, such as pollens, foods, and house dust mite. Whilst in most people these substances (allergens) pose no problem, in allergic individuals their immune system identifies them as a 'threat' and produces an inappropriate response.4

Exposure to similar allergens leads to different patterns of allergic disease in children.[PAL06, BIS08] This could result from different patterns of allergen entry. The skin acts as a barrier to allergen entry. Skin barrier defects, commonly present within the population, have been linked to more severe patterns of sensitisation and worse allergy-related disease.[BAS08] The presence of exposure to particular allergens can thus be related to symptoms through allergy testing and this will help distinguish between sensitised and non-sensitised individuals, thus offering directions for better management.[BAS08]

To take the GP Buddy allergy modules, click here.

Symptoms of allergy

The symptoms of allergy are vast and can often be confused with other conditions. Some common presentations of allergy include rhinitis, asthma, eczema, anaphylaxis, food allergy and occupational allergy. Within these conditions there are a number of symptoms which at first presentation may not necessarily be attributed to allergy, and as such may result in poor patient management.


  • Abnormally dry skin
  • Dry depigmented patches
  • Erythrodermic rash
  • Itching
  • Oozing vesicles
  • Crusted vesicles
  • Eroded vesicles
  • Erythematous plaques
  • Lichenified, slightly pigemented, excoriated plaques
  • Exhaustion
  • Thick, pale excoriated plaques


  • Wheezing
  • Breathlessness
  • Chest tightness
  • Coughing


  • Stuffed-up nose
  • Runny nose
  • Post nasal drip
  • Red itching eyes
  • Watering eyes
  • Repeated sneezing
  • Headache
  • Nasal itching
  • Facial pain
  • Ear pain
  • Tiredness

Food Allergy

  • Mild symptoms
  • Itching in the mouth
  • Urticaria
  • Intense itching
  • Swelling of the face
  • Feeling very hot or cold
  • Rising anxiety
  • Pale/flushed appearance
  • Mild wheezing or cough
  • Abdominal pain
  • Nausea
  • Decreased level of consciousness
  • Diarrhoea
  • Severe symptoms
  • Difficulty in breathing
  • Wheezing
  • Hoarseness
  • Croupy/choking cough
  • Very pale/blue lips
  • Unresponsiveness
  • Collapse


  • Shortness of breath
  • Wheeze
  • Swelling in the throat
  • Cough
  • Rhinitis
  • Nausea
  • Vomiting
  • Diarrhoea
  • Swelling of skin (lips and eyes)
  • Stomach pain
  • Urticaria
  • Flushed skin
  • Itch without rash
  • Loss of consciousness
  • Low blood pressure
  • Headache
  • Seizure
  • Substernal pain

Adapted from WAO white book, 2011 and NICE guidelines 2011.3,5


What may seem as the obvious trigger may just be the "tip of the iceberg". Since most atopic individuals are allergic to more than one allergen, it is important to identify all the allergens that contribute to the symptoms to ensure optimal symptom relief.

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Allergy can be identified through a three step process:

1. History

Diagnosing allergy starts with a physical examination and an allergy-focused patient history. Asking just a few key questions will provide you with a detailed history, (for food allergy, indicate if the allergy is IgE- or non IgE-mediated) and allow you to correctly manage your patient. The key questions should focus around:

  • Patient, environmental and family history
  • Suspected allergens
  • Time course between exposure and symptoms
  • Symptoms

2. Testing

Assess the need for testing

If the patient history suggests an IgE-mediated allergy, conduct a blood test (allergen-specific IgE) or by trained, competent clinical staff, in an environment with facilities to manage anaphylaxis5 Specific IgE testing can be performed on any patient irrespective of age, allergic symptoms (i.e. eczema) and medication.

Download a clinical toolkit to learn more about which allergens to test for.

When taking blood for a test a 1 ml sample of whole blood is sufficient to test for up to 10 different allergens.

Interpretation of test results

Results should be read in conjunction with the clinical history.

3. Management

Avoidance or reduction in exposure to allergens can alleviate or reduce symptoms.

In food allergy, in consultation with a dietitian, the food should be removed from the diet. In aero allergy, symptoms can be managed with medication, however, patients, particularly patients with asthma, could be at risk of severe reactions and as such advice should be given on reducing these allergens from the environment.5

For management tools view the resources section.

Case history alone is not enough - don't guess, test

Adapted from Duran Tauleria, 2004 and Niggemann 2008. Allergy 2004;59 (suppl 78): 35-41 and Pediatr Allergy immunol 2008; 19:325-331. Study among patients with symptoms of eczema, wheezing and/or asthma, and rhinitis in primary care.3,4

By adding the above considerations to an IgE antibody test result, combined with previous medical history and a physical examination, the allergy investigation can be fine-tuned to give a highly informative picture.

  1. Allergy-Ireland. Available from allergy-ireland.ie/media-publications/allergy-epidemic/; last accessed August 2016.
  2. Pawankar R (Ed) et al. White book on allergy, 2011; World Allergy Organisation UK.
  3. Pawankar (Ed) et al. White book on allergy, 2011; World Allergy Organisation UK.
  4. Allergy UK. Available from https://www.allergyuk.org/what-is-an-allergy/what-is-an-allergy last accessed September 2015.
  5. National Institute for Health and Clinical Excellence. Food allergy in children and young people (CG116). 2011. London: National Institute for Health and Clinical Excellence.
  6. Eggleston PA. Control of environmental allergens as a therapeutic approach. Immunol Allergy Clin North Amer. 2003;23(3):533-547.