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Do You Really Have a Penicillin Allergy?
Chances are you don’t, doctors say, and are avoiding this antibiotic without cause
5-minute read
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Key takeaways
- Many allergies fade over time, including an allergy to the antibiotic penicillin.
- Avoiding penicillin can increase the risk of antibiotic resistance and serious infections.
- Allergy testing shows that about 90 to 95 percent of people who believe they are allergic to penicillin can tolerate it.
If you’re like the 1 in 10 Americans who think they have a penicillin allergy, you’ve probably been avoiding the drug for decades. But only about 1 percent of people actually experience an allergic reaction when they take the antibiotic, and avoiding it needlessly can actually be harmful, experts warn.
Even someone with a confirmed allergy to penicillin can outgrow it. In fact, more than 90 percent of people with penicillin allergies are no longer allergic 10 years later, according to the American Academy of Allergy, Asthma & Immunology.
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In many cases, people were incorrectly labeled as allergic. In the ’50s, ’60s and ’70s, penicillin was “used like candy,” Dr. Bruce Gordon, a retired Massachusetts otolaryngologist, told AARP in an earlier version of this article. “A lot of kids had viral infections and developed rashes while taking penicillin. But it was because of the virus, not the penicillin. Still, nobody wanted to risk it because of the few people who have true and severe allergic reactions.”
The allergy label can be especially dangerous in older adults, says Dr. Elizabeth Phillips, a professor of medicine and John A. Oates chair in clinical research at Vanderbilt University Medical Center in Nashville. A big reason: It can prevent people from receiving the most effective antibiotic to treat their infection, and older individuals are more susceptible to severe outcomes from routine infections due to underlying health issues and age-related changes in the immune system.
But older adults are more likely to report being allergic to penicillin, according to a 2025 report in the Journal of the American Geriatrics Society. A separate study, published in 2024 in Annals of Allergy, Asthma & Immunology, evaluated 2,345 residents across 20 Massachusetts long-term care facilities and found that just over 23 percent of the older adults reported penicillin allergies.
One explanation could be how the drug was originally administered. Before penicillin was in liquid and pill form, it was given as an injection. So it could be that reactions reported in its earlier days of use were due to the injection itself rather than the medication.
This isn’t reflective of how penicillin is made or used today, Phillips explains. “It’s not really a fair comparison,” she adds.
The paradox of penicillin
When patients report an allergy to penicillin, they are usually prescribed an alternative antibiotic. Those alternatives are often broad-spectrum antibiotics, which fight a wide range of bacteria and are typically used when a patient has a serious infection or when it’s unclear what bacteria is causing the infection. Because they are designed to wipe out various types of bacteria, they can kill both harmful and helpful bacteria, which can disrupt the gut microbiome. It can also lead to more illness.
“We want to use the most narrowly effective antibiotic possible, and if allergies are getting in the way of that, [we] gather more information,” about the suspected allergy, says Dr. Kimberly Blumenthal, a professor of medicine at the Mayo Clinic College of Medicine and Science in Jacksonville, Florida.
“When you start to broad-brush and kill off good bacteria that normally keep other bacteria in check, bacteria like Clostridium difficile [C. difficile, or C. diff] can thrive and cause serious problems, including diarrhea, dehydration, sepsis and death,” explains Dr. Anita Gupta, an adjunct assistant professor of anesthesiology and critical care medicine and pain medicine at the Johns Hopkins University School of Medicine in Baltimore.
Older adults have a higher risk of C. diff, due to more frequent interactions with the health care system and age-related changes that affect the immune system.
Using broad-spectrum antibiotics also leads to more drug-resistant bacteria. “If we can stop the use of these broad-spectrum drugs that kill everything, we won’t see as much C. difficile and resistant bacteria,” says Dr. Michael Blaiss, a clinical professor of pediatrics at the Medical College of Georgia at Augusta University. A 2019 report in the Journal of General Internal Medicine shows that people reporting penicillin allergies were 14 percent more likely to die from any cause compared with those without the allergy. A study out the year before in The BMJ finds that those reporting a penicillin allergy experienced 69 percent more staph infections and 26 percent more C. diff infections than those without the allergy.
What’s more, an alternative antibiotic may not be as effective and may be more expensive than penicillin, says Barbara Santevecchi, a clinical associate professor and infectious diseases clinical pharmacy specialist at the University of Florida College of Pharmacy in Gainesville. “There’s not always an alternative antibiotic that’s just as good [as penicillin],” Santevecchi says.
Penicillin Allergy.
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Penicillin allergy symptoms
Allergists say doctors and patients have long been confused about what a true penicillin allergy looks like. It’s not, for instance, vomiting. An allergic reaction occurs within a few hours of taking the drug and may include itchy hives, swelling of the face and other areas, and wheezing or difficulty breathing. Anaphylaxis can also occur in more serious cases.
“The timing is important; this happens within a few hours,” Blaiss says, and not weeks later. “A lot of doctors say, ‘You might be allergic to penicillin. Just avoid it.’ ”
Penicillin allergy testing
If you are allergic to penicillin — or think you are — talk to your doctor about your history and the symptoms you have when you take the medication.
Clinicians will likely stratify you based on your risk of an allergy. The more specific you can be about any symptoms you experience, the more likely the clinician is to determine whether they are actually due to an allergy. Share details about when a reaction occurred, what it was like and other antibiotics you’ve taken in the past, Santevecchi says.
Your doctor can test you for a penicillin allergy by administering the drug and monitoring your reaction. It’s important to note that you can’t get the test while on some medications, including beta-blockers or antihistamines, so your doctor may adjust your routine for the test, Blaiss says.
Approximately 90 to 95 percent of people who believe they have a penicillin allergy can tolerate the test just fine, research shows.
“I’ve seen one person in 35 years develop some wheezing and hives after the test,” Blaiss says.
You may not need a penicillin allergy test at all. For example, if your medical record lists vomiting a week after starting penicillin as the reason you’ve avoided the drug ever since, Blaiss says you can probably take it safely.
Determining if you have an allergy “matters even more” as an older adult, Phillips says, since you may have a higher risk of side effects and toxicities from alternate antibiotics.
What’s more, some doctors may be less likely to perform surgery on you if they see the allergy label on your chart, Phillips adds.
And keep in mind: The best time to bring this up isn’t when you’re sick and may need an antibiotic, Santevecchi says. Bring up any allergy concerns during a routine exam, so you’ll know which antibiotics you can take the next time you get an infection.
The key takeaways were created with the assistance of generative AI. An AARP editor reviewed and refined the content for accuracy and clarity.
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