When you were a kid, you may have been told you were allergic to penicillin. For decades, doctors commonly diagnosed allergies to penicillin —and told many people to avoid it. But the reality is that many people told they were allergic to penicillin don’t have an allergy. In fact, according to the Centers for Disease Control and Prevention, 10 percent of Americans have been told they have the allergy, but less than one percent is allergic. How can you tell if you have a true penicillin allergy? You’ll need a test for an accurate diagnosis.