Allergies occur when the human immune system starts fighting substances that are in fact quite
harmless, like pollen, dust or foods. The more sensitive the immune system is to a particular
substance that triggers an allergic reaction (allergen), the more severe the resulting symptoms are.
Allergies may cause watery or red eyes, sneezing attacks, a stuffy nose, an itchy rash or stomach
ache. In rare cases an allergy may lead to an anaphylactic shock. Then the airways become narrow,
making it very hard to breathe, and there is a severe drop in blood pressure. Anaphylactic shock can
become life-threatening if not treated immediately.

Various tests can be used to find out what kind of substance is causing an allergic reaction: skin
tests, blood tests and provocation tests. Your doctor will usually decide which test to use based on
your description of the symptoms and your medical history.

How are skin tests done?

Skin tests are easy and quick to do, so they are often the test of choice for determining what is
causing an allergy. Possible allergy triggers are applied to the skin and the reactions are observed.
This is most commonly done on the inside of your lower arm, or sometimes on your back.

Skin prick test

In this test, the doctor puts drops of different watery solutions containing allergens (like pollen or
trace amounts of animal hair) on various marked positions on your skin. Your skin is then pricked a
little at each site so that the allergens can enter the skin. To test for a food allergy, the food can be
pricked first – before pricking your skin.

If you’re allergic to the substance, your skin will react: On light-colored skin, the marked site will
become red and a small bump (wheal) will appear. Wheals develop on dark skin too, but they're
more the color of the surrounding skin or a bit lighter. The skin prick test is mainly used to detect
allergies that trigger an immediate reaction when they make contact with the skin – such as hay
fever or some food allergies.