with Elena Resnik, Kimberly Blumenthal & Teresa McFale
17 Jul 20264 min read43m
TL;DR
Around 10% of Americans believe they are allergic to penicillin, but studies show 90% of them are not — and in allergist Kimberly Blumenthal's own practice of ~3,000 suspected cases, roughly 99% were not truly allergic. The false belief, usually inherited from a childhood rash misattributed to the drug, causes patients to receive inferior, more expensive, and riskier antibiotics instead. Host Steven Dubner tells his own story of months of illness that may have been shortened had he not been carrying a false penicillin allergy label.
Key Moments
Kimberly Blumenthal
“I realized that what we were calling allergy was mostly side effects.”
Blumenthal describes the insight from medical school that drove her career focus on penicillin allergy misdiagnosis.
“We should be screaming from the rooftops. This is a misdiagnosis. Everyone has something on their chart that's wrong and nobody is screaming about taking it off.”
Blumenthal is responding to Dubner's question about whether any other medical field has a comparable false-positive rate.
“He used to fight with people to get them to recognize that their issue was food allergy. And now he fights with people to get them to recognize that their issue is not food allergy.”
McFale is describing the shifting challenge faced by renowned food allergist Dr. Hugh Samson over his 40-year career.
Freakonomics Radio is hosted by Steven Dubner and explores the hidden side of everything through an economic lens. This episode revisits a 2024 investigation into penicillin allergy misdiagnosis, featuring allergists Elena Resnik and Kimberly Blumenthal, and medical anthropologist Teresa McFale. The episode was updated and replayed in July 2026 after significant listener response.
Takeaways
1
90–99% of penicillin allergy labels are wrong Studies show 90% of people labelled penicillin-allergic can actually tolerate it. In allergist Kimberly Blumenthal's practice of ~3,000 such patients, only about 20 tested truly allergic. The label typically originates from a childhood rash that was more likely caused by the infection itself than the antibiotic.
2
Getting 'delabeled' is a simple three-step process An allergist can clear a penicillin allergy label with a skin prick test, an intradermal test, and finally an oral challenge dose of amoxicillin with two hours of observation. If the first two tests are negative, there is a 95%+ chance of passing the oral challenge. The whole process takes two office visits.
3
False allergy labels lead to worse medical care Patients labelled penicillin-allergic are routinely given alternative antibiotics that have worse side-effect profiles, higher complication rates, and greater cost. In some cases, alternatives like vancomycin increase the risk of drug-resistant bacteria. Penicillins remain the safest, cheapest, and most reliable antibiotics available.
4
Allergy skin tests are 150-year-old technology with 50–60% false positive rates for food The skin prick test for food allergies was invented by UK physician Dr. Charles Blackley in the late 1800s and remains the primary diagnostic tool today. For food allergies, 50–60% of positive results are false positives. False negatives are much rarer, making these tests more useful for ruling out allergies than confirming them.
5
Pharma lobbying helped inflate EpiPen demand and allergy awareness Mylan Pharmaceuticals hired more lobbyists than any other US company over one 10-year period, lobbied to get EpiPens placed in schools, partnered with Disney on allergy-awareness children's books, and secured an FDA relabeling that expanded the eligible patient population. EpiPen prescriptions rose three to four times between the 1990s and 2018–2019, making it difficult to disentangle genuine allergy increases from commercial demand creation.
6
The 'old friends' hypothesis may explain rising allergy rates Originally called the hygiene hypothesis, the 'old friends' hypothesis proposes that modern immune systems are under-trained because we no longer encounter the bacteria, viruses, and fungi our immune systems evolved alongside. Younger siblings historically had lower allergy rates, likely because older siblings brought home exposures. Rates of food allergies have continued rising even as asthma and hay fever levelled off in the 1990s.