There are TWO different skin allergy testing. I am deathly afraid of needles -- just like a kid. I have zero tolerance for pain. The one where they use an injection -- it is unnecessary, painful, and can make you MORE sensitive to things. A doctor who was not my regular doctor did this -- and my regular doctor wished that I had not. I was on vacation and I was sick -- which is also a bad time to test anyway. Big mistake.
The kind that I have had done (and mommafirst discusssed) is the scratch test, consisting of tiny pokes -- and you barely should feel it -- it is done on your back. Then you should re-check after 5 hours to see if there is a delayed reaction (sometimes they don't tell you this.) And as I said many kids perceive it as TICKLING. Red and itchy means there is a positive reaction. They also quantify is as 1 plus through 4 plus to ley you know HOW severe your allergy is.
The way my doctor does it, is on 3 different days, because otherwise you run the risk of a reaction and again you may become more sensitive. If your doctor does not do it this way, ask! Also you should get an IGe level. If for instance, your allergy testing shows nothing and your IGe level is high, it can be a strong indication of chemical sensitivities. You're are lucky if they find things in tests, because it takes out a little bit of the guesswork.
There are also blood tests (expensive)they can do for specific allergies. I don't know much about these. I know that insurance frequently does not cover them. But most insurance companies do cover skin testing and that really does give you an indication. They cannot test for every substance in the world.
The tests are in 3 groups 1) environmental 2)foods There is a third, I can't remember what it it is called. They test you for hundreds of things. They can even test for spices. There are actual test for chemicals, but my doctor won't test for these -- if you are chemically sensitive, these tests can make you worse.
If I think these tests are mild...anyone can tolerate them. I am a huge baby.