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How are allergies diagnosed?

The most common way to test for Type I allergy is using a skin prick test (SPT).  This is always completed in a clinic or hospital (never at home). A small amount of allergen will be put on a flat part of the body (e.g. inner arm) and a lancet will be used to prick the skin (most patients do not feel anything other than a little pressure); any allergen is then blotted away. After 15 minutes the arm is examined by a medical professional who will ascertain if there has been a reaction.  This along with a full medical history is used to diagnose allergies. A list of common allergens that can be used for SPT can be found here (link to list).

For some people SPT is not appropriate, e.g. those with certain medical conditions or on certain medications that they must take regularly, in which case a blood test can be taken.

The ‘gold standard’ in allergy diagnosis is a Challenge Test, this test involves consuming or inhaling increasing amounts of the suspected allergen and assessing for a reaction.  This test must be under supervision of medical professionals.

To test for a Type IV allergy the most common way to diagnose is a ‘patch test’. Patch testing is carried out by a clinician and entails having patches pre-loaded with allergens, stuck to your back.  Again, this will be carried out in a clinic.  You will need to keep that patches in place for a couple of days, you will then have them removed.  Your clinician will check the results after a further couple of days.