Diagnosing Allergies - How to Diagnose an Allergy?


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Some people have such a violent reaction to certain allergens, such as anaphylaxis, that it is relatively easy to diagnose their allergy. However, many people have either quite subtle reactions or, in the case of a food allergy, there are so many different possible causes that it can be hard to correctly diagnose the allergy or its severity.

Symptoms that might indicate an allergy

Symptoms commonly experienced by those with allergies include sneezing, having a runny nose, suffering from burning or dry eyes and experiencing skin irritation. These can vary greatly in severity from person to person. This is by no means an exhaustive list – allergies affect different people very differently and the range of possible symptoms reflects this. These are merely arguably the most common signs of an allergy. While these symptoms do not automatically provide a diagnosis, being aware that you could be suffering an adverse reaction to one or some allergens is the first step.

Make an allergy-symptom journal

It is a good idea to make a diary detailing the occurrence, frequency and nature of the symptoms you are concerned about. Include in this as much detail as you are able, such as anything unusual in your diet, or if you have changed washing powder for example. If you can start to see a pattern emerging it will be that much easier for the allergist to begin to help you. It may also mean that you realise that, for instance, you only experience rashes after using a particular brand of cosmetics or changing your brand of washing powder. 

Make an appointment with an allergist

If this does not help then it is best to make an appointment with an allergist so that they can properly identify and diagnose your allergies. Although it is tempting to go and see an allergist straight away, it is a good idea to complete the above step first and then take this diary with you to your appointment. This may help you to properly explain your symptoms and their frequency to the allergist and they will have a more informed idea of your case as a result. In this way, they should be able to alleviate your discomfort more quickly.

Allergy Skin Tests

If it seems unclear as to which allergen or allergens are causing you to have an allergic reaction, your doctor or allergist can perform certain allergy tests to try and determine what it is that you are allergic to. There are a few different tests that can be done; which your doctor or allergist chooses to do will depend on the condition of your skin and the nature of the symptoms you have been suffering from.

Skin prick test

If the cause of your allergy is not immediately obvious, your doctor or allergist may perform a skin prick test to identify which allergens are causing your body to react.

This involves using a needle to insert a small quantity of a certain allergen slightly under the skin’s surface, commonly on your inner forearm. If you react to that allergen then within approximately 20 minutes the area will develop a weal (a swollen area with a raised circle). Evidence of an allergy or a more severe allergy is shown the larger the area of skin is that has had a reaction. Although uncomfortable, the skin prick test should not be painful.

Skin patch test

This test will be administered if your allergy symptoms include rashes, or contact dermatitis. If this is the case, it is likely that your body is reacting to a certain allergen, or allergens, when they come into contact with the skin. This test involves small metal discs being covered in allergens that are most likely to be causing a reaction. These different discs are taped to you, usually to your back, and are left in contact with the skin for a period of 2 or 3 days. The discs will then be removed, your skin examined and any reactions noted and analysed. If a red and/or itchy area has appeared where a disc has been, then this particular allergen is the one that your body is allergic to. This is a very safe, painless form of allergy testing.

Blood test

This test is much more accurate than either of the above as a sample of your blood is taken and specifically analysed in a laboratory by experts. A test known as a RAST (Radio Allergo-Sorbent Test) is conducted on your blood. This details exactly the amount of IgE antibodies (those that provoke reactions to certain allergens) are in your blood and therefore how allergic you are. The scale that is used ranges from 0 to 6, with 6 indicating the greatest number of antibodies, and thus also the most severe allergic reaction. This test is sometimes used if you have severe eczema, for example, or another skin condition or problem that would make tests conducted on the surface of the skin too uncomfortable.


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