AARP Hearing Center
Am I Really Allergic to Penicillin?
Many people who avoid this common antibiotic aren’t actually allergic to it. Here’s how to find out safely
James Yates
How do I know if I’m still allergic to penicillin?
Some medical labels have a remarkable ability to follow us through life. A penicillin allergy is one of them. If that diagnosis was put on your chart decades ago, you may still be carrying it around without knowing exactly what caused it — or whether it’s still true.
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About 10 percent of U.S. patients report having a penicillin allergy, but fewer than 1 percent really are allergic, according to the Centers for Disease Control and Prevention. There are several reasons for this. One is that your original reaction may never have been an allergy. For instance, as a child, you may have developed a rash while taking penicillin for an infection, but the rash could have been caused by the infection itself. Viral and bacterial infections can produce rashes. Yet years later, all you remember is, “I took penicillin and got a rash.”
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Another common source of confusion is the difference between an allergy and a medication side effect. Nausea, vomiting or diarrhea after taking penicillin can certainly make you feel miserable, but those are generally safe side effects, not allergic reactions. A true allergic reaction can involve hives, swelling, wheezing, difficulty breathing or, in severe cases, anaphylaxis, which may be life-threatening.
One more possibility: You may have had a penicillin allergy years ago, but you no longer have it now. Approximately 80 percent of people with a true penicillin allergy lose their sensitivity within 10 years.
Why does this matter? Because a penicillin allergy label can significantly narrow your doctor’s antibiotic choices. Penicillin is effective against many common bacterial infections, and when doctors avoid it due to an allergy label, their patients may instead receive broader-spectrum antibiotics. Those alternatives can yield more adverse effects, such as increased antibiotic resistance and infections like Clostridioides difficile, often called C. diff.
Researchers have also noted links between a penicillin allergy and worse patient outcomes, though it’s unclear whether those findings are related to the allergy, the allergy label or other factors. One study looked at more than 11 million adults and found that those with a recorded penicillin allergy had a 14 percent higher risk of death from any cause than people without the allergy label, though that doesn’t mean the allergy label itself caused the death.
If you carried a penicillin-allergy label for 20 or more years, what should you do today? Speak with your doctor about whether you should be evaluated by an allergist or immunologist.
The evaluation begins with a careful medical history. Depending on what originally happened and how long ago it occurred, an allergist may perform skin testing and, when appropriate, a supervised oral challenge. One clarification is important, even if your allergy is confirmed. A penicillin allergy does not automatically mean you can never receive a cephalosporin, which belongs to the same family of antibiotics. Reactivity varies among those medications, but the risk with third-generation cephalosporins, developed after the earlier versions, is less than 1 percent.
Your doctor will determine which antibiotics are appropriate for you based on the particular drug and the nature and timing of your previous reaction. Medication has changed over the years, and our understanding of drug allergies has changed along with it. The goal of allergy evaluation is to determine as safely and accurately as possible whether that old label belongs in your medical record.
If testing shows that you aren’t allergic to penicillin, removing the label can give your doctor more appropriate choices the next time you need an antibiotic. But remember, the safest answer comes from a supervised evaluation. Please, never do a test dose at home.
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