Are You Really Allergic to Penicillin? (Update)

**Stephen Dubner** (0:01)
Freakonomics Radio is sponsored by Southern New Hampshire University. The best investments are the ones you make in yourself, and no one knows that better than Southern New Hampshire University. With more than 200 online degree programs, no set class times, and low online tuition, Southern New Hampshire University is built to fit your life today and set you up for success tomorrow. Education is an investment. Why not make it a smart one? Apply for free at snhu.edu/freakonomics.
Freakonomics Radio is sponsored by Progressive. Insurance isn't one size fits all. That's why drivers have trusted Progressives. Name your price tool for years. Just tell Progressive what you want to pay, and they'll show you coverage options that fit your budget. Visit progressive.com to find a car insurance rate that works for you. Progressive Casualty Insurance Company and Affiliates. Price and coverage match, limited by state law.
Freakonomics Radio, sponsored by hotels.com. hotels.com gives you access to hundreds of thousands of hotels worldwide. And when you join for free, you can save up to 20% instantly with member prices. Plus every stay earns rewards. So when you book one trip, you're already lowering the cost of the next one. hotels.com is simple, rewarding, and designed to help you get more out of every stay.
Sign up for free and book today. hotels.com. It's all in the name.
Hey there, it's Stephen Dubner. Until last year, I believed that I was allergic to penicillin. That belief caused me some unnecessary trouble. And I am not alone. As I learned, 10% of Americans believe they are allergic to penicillin, but true penicillin allergies are much rarer than that. So we made an episode about it, which we first published last year. Since then, we have heard from a ton of listeners who checked out their own alleged penicillin allergies. And you may have run across this topic on the HBO medical drama, The Pit.

**Theresa MacPhail** (2:12)
Hanging a gram of Ansef. Wait, he has a penicillin allergy. No, Penves was negative. We're okay.

**Elena Resnick** (2:16)
My mom said I got a rash with anoxicillin. I was too.

**Kimberly Blumenthal** (2:19)
Yeah, probably not a true allergy. Go ahead and give it to him.

**Theresa MacPhail** (2:23)
Most people who think they have a penicillin allergy actually don't.

**Stephen Dubner** (2:27)
But many, many people still avoid penicillin based on a faulty diagnosis. So we decided to replay this episode for you today. As always, we have updated facts and figures as needed. All your feedback is welcome. Our email is radio at freakonomics.com.
They say it is always a good idea to express gratitude. So here's what I'm most grateful for right now. My health. For much of 2024, I was sick. It started in the spring with a cough that turned into a respiratory infection. That turned into a whole other thing. And for a few months, I was miserable. It hurt to talk or swallow. Every time I laughed, it would trigger a coughing fit, which is a problem because I like to laugh. Thanks to the cough, I couldn't sleep through the night. I also had some ferocious night sweats and crazy dreams. During the day, my entire body ached like I had been hit by a car. Also no appetite, no energy.
Physically, it was the worst few months of my life. But at least I got a story out of it.
This one.
Today's episode is about penicillin.
You may remember the famous story of how penicillin was discovered accidentally nearly a hundred years ago by Alexander Fleming. This was at St. Mary's Hospital in London. Fleming was just returning from holiday. In his lab, he had left behind a petri dish where he'd been culturing bacteria, and he found some mold growing in the dish. Interestingly, where the mold grew, the bacteria did not. It turned out that this mold juice, as Fleming called it, could kill many types of bacteria, not just the one growing in that petri dish. Penicillin was eventually used to treat strep throat, meningitis, dental infections, gonorrhea, and much more. It came to be thought of as something like a miracle drug. The penicillins are in fact a family of antibiotics, including amoxicillin, ampicillin, methicillin, and several others. All these years later, they are still among the safest, cheapest, and most reliable drugs around. They have saved hundreds of millions of lives. Even with all the new antibiotics since then, penicillin is still prescribed at the highest rate of any antibiotic. But there's one big problem. 10% of Americans, more than 30 million people, are allergic to it. At least that's what the conventional wisdom says. But the new year is also a good time to tear down conventional wisdoms, especially if they are disastrously wrong. And this one is. So today on Freakonomics Radio, why do so many of us think we have this allergy?