NEWS YOU CAN USE: Allergic to Penicillin? You May Not Be: Nineteen out of 20 people who have been told they are allergic to penicillin are not truly allergic to the drug. “Though an allergy can develop at any age, penicillin allergies are often first recorded in childhood, when penicillin is the No. 1 antibiotic prescribed, she said. If a child on penicillin develops a rash or other symptom and it is erroneously attributed to the drug, the allergy label sticks, often for life. . . . There is no question some people have potentially life-threatening allergic reactions to penicillin, but the label appears to have been applied far too broadly, experts say. About 10 percent of Americans report having a penicillin allergy, and the rate is even higher among older people and hospital patients, 15 percent of whom have a documented penicillin allergy.”