Are You Really Allergic to Penicillin? (Update)

A decade ago, Stephen Dubner learned from his doctor that the penicillin allergy listed in his medical chart was almost certainly wrong. He didn't follow up. Then, in 2024, a months-long respiratory infection and a course of the alternative antibiotic azithromycin failed to help. Only after an allergist cleared him—through skin prick tests and an oral challenge—could Dubner take amoxicillin. The healing began. His story is typical: roughly 10% of Americans believe they are allergic to penicillin, but fewer than 1% actually are. The gap between perception and reality has serious consequences.

How a False Allergy Label Takes Hold

The confusion starts early. Allergist Kimberly Blumenthal of the Mayo Clinic explains that when children get infections, they often develop rashes. If that infection is treated with an antibiotic, the rash is misattributed to the drug. "Children get rashes when they have infections," she says. "There's misattribution of allergy." Often the infection was viral anyway, making the antibiotic unnecessary. That childhood event gets entered into a medical record, and the label follows the patient for life. Blumenthal estimates she has seen roughly 3,000 patients who believed they were penicillin allergic; she remembers only two severe reactions. "99% are not," she says. "This is a misdiagnosis."