A skin test is an examination, showing whether a person is allergic to certain substances. There are several types of skin test. The kind of test a person gets, depends on the type of allergy that is suspected.
An allergic response is an excessive reaction of the body to a substance that can actually do no harm. Such a substance is called an allergen. Allergens are found in the air, in food products, in medications, in insect venom, but also in skin care products and perfumes. Symptoms associated with an allergic response include hay fever and food allergy. The skin test is a quick way to determine whether there is this type of allergic response.
In a skin test, the allergen is brought on or just under the skin with injections or with special needles. The intention is to trigger an allergic response in the skin after the allergen in question is absorbed in the epidermis. If there is an allergic response, a swelling can be seen on that location with a red spot around, which can also itch.
The following types of skin test can be used:
- The prick test (percutaneous test). This is used in case of suspected allergy to inhaled allergens, food allergens, drugs or insect venom. In this test, a drop of test fluid is put onto the skin and with a needle pricked through the fluid into the skin. This is only to reveal the presence of antibodies. For a definitive diagnosis of, for example, food allergy or medicines allergy, a provocation test is often necessary. The response can be read after about 20 minutes.
- The intradermal test. This is mainly used in case of suspected insect venom allergy and drugs allergy. The test fluid is injected into the skin. An intradermal test is usually performed in stages, whereby each time is tested with a higher concentration. The response can be read after about 20 minutes.
- The patch test (epicutaneous test). This is used in case of suspected contact allergy, but can also be very useful in case of suspected hypersensitivity to drugs, for example corticosteroids. The substances to be tested are applied on small cloths, which are stuck to the back with patches and removed after two days. On that day and one or two days after, the response is read.