If your child has developed rashes, and you're not sure what the cause is, then it is wise to have them undergo allergy testing. It's a safe and comprehensive way to determine what is causing the skin irritation. Because it can be nerve wracking anytime you bring your child in to see a doctor, here is a overview of how the tests are administered.
Before The Test
In order to create a baseline, the doctor or nurse will wash your child's skin and then apply two substances. The first is saline. If the child has a skin reaction to saline(which most people are not allergic to ), then they are going to have hyper sensitive skin, which will guide the doctor's analysis.The next step is two swab the skin with histamine. This should cause a reaction. If your child has no reaction to the histamine swab, then the skin tests might not be adequate and the doctor might jump right ahead to blood work.
Percutaneous Skin Tests
This is the most common sort of allergy test you will run across. The doctor will take a small pin (called a lancet) that has a bit of a potential allergen on it, and make a tiny prick on the surface of the skin. The pin/needle does not go deep into the skin. The doctor will often draw circles on the skin and number these circles so that if one area develops a rash, they can correlate it to a particular substance that is causing the reaction.
Intradermal Skin Testing
This is less common and is only used when the doctor does not see results with the percutaneous test, yet still feels that there is something causing an allergy. It is also used to look at allergic reactions to two specific substances: insect venom (such as bee stings) and penicillin. The doctor will use a needle, not a pin, to inject the substantial into the skin. The test is considered to be more accurate, so if the results of the pin test are inconclusive, this is the next step.
Skin Patch Test
The skin patch test is done without needles or pins. Instead, a piece of the potential allergen (cotton, plastic, perfume, wool) is placed on the skin and then covered with a patch. The doctor will then tell you to keep it covered for at least a day. This test is excellent at determining allergic reactions that will only show up with prolonged contact (such as with your child's clothing and recurring contact dermatitis).
These tests are done if your child is on a medication (such as an anti-histamine) that will prevent rashes from flaring up. The doctor will draw blood, and then mix the potential allergens with the blood to see if there is a reaction.