In this test, the nurse administers a small amount of penicillin on the skin and then places a small amount under your skin with a tiny needle. A positive reaction to either test will cause a red, itchy, raised bump. A positive result indicates a high likelihood of penicillin allergy. A negative test result usually means you’re not allergic to penicillin. Negative skin tests are usually followed by ingesting a small amount of penicillin and then progressively a larger amount to confirm that there is no penicillin allergy.