To identify the possible allergens which may be causing your problems, your doctor or allergist may perform some specific tests.
The most likely test is called a skin prick test (SPT). To do this, your doctor will place a small drop of allergen solution on your forearm and prick your skin through it with a small needle. This prick is not harmful at all. A positive reaction will be seen as a small papule (blister) surrounded by a red area of skin at the site of injection. This response, which will tickle a little but not hurt, is called a “wheal and flare response". The response will be measured after 15 – 20 minutes and any response will disappear soon afterwards.
Alternatively, your doctor could take a small blood sample and send to a specialist laboratory to determine your sensitivity to a series of allergens. These tests are slower and much more expensive to perform and so are usually reserved for patients with skin problems which make it difficult to perform skin prick tests or for patients with a history of severe anaphylaxis in whom performing the test might cause a potentially dangerous severe reaction.
The skin prick test and the blood test for allergy are only used to confirm a diagnosis suggested by your history as many individuals without allergic disease show positive responses. This is why sending off a blood or hair sample yourself is not a good idea.
Your allergist may also perform some more specialised tests. These might include an inhalation provocation test for suspected asthma, patch tests for eczema or urticaria and oral food provocation tests for food allergy. Such tests should only be done by specialists.