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Many people who as infants exhibited an allergic reaction to penicillin will grow out of it. Getty Images

If you’re one of the 25 million Americans who’ve self-reported a penicillin allergy, you may not be allergic to this common medication after all.

Not only is penicillin the first antibiotic doctors ever used, it’s also still considered to be one of the safest and most effective medications. While several antibiotics have fallen out of favor as resistance rates have increased, penicillin remains a mainstay treatment for many illnesses.

But many people falsely believe they’re allergic to the medication, which results in doctors turning to other antibiotics that may be less effective.

Physicians at McMaster University in Ontario, Canada, reported February 25 that 9 out of every 10 people who believe they’re allergic to penicillin either aren’t allergic at all or have only had mild intolerance. Further, 8 out of 10 people who’ve had an allergic reaction to penicillin 10 or more years ago will likely be fine now.

These physicians note that penicillin is the most commonly reported allergy, but 90 to 95 percent of these people aren’t actually allergic at all. They state the reason for this is likely due to parents mistakenly labeling intolerances of their young children as “allergies.”

“Intolerance typically refers to side effects of a medication, and medication side effects and allergies are frequently confused,” said Dr. Blanka Kaplan, director of the Drug Allergy and Desensitization Center at Northwell Health in Great Neck, New York.

“Intolerance or side effects refer to an undesirable effect of the medication that isn’t mediated by the immune system. They’re frequently caused by the way medications work,” Kaplan added.

“Many people incorrectly assume that having an allergy to penicillin is carried through the family,” said Dr. Amy CaJacob, assistant professor of pediatric allergy and clinical immunology in University of Alabama Birmingham’s department of pediatrics. Despite this belief, the American Academy of Allergy, Asthma, & Immunology states that “there is no predictable pattern to inheritance of penicillin allergy.”

Penicillin antibiotics are part of a broader family of antibiotics called beta-lactamase antibiotics. In addition to penicillin, these include popular medications called cephalosporins. Because of cross-reactivity, people who claim to be allergic to penicillin are also limited in which cephalosporins they may receive.

Not only is an unverified penicillin allergy bad for people, but it’s also bad for the greater healthcare system. Those who report being allergic to penicillin are often offered more expensive antibiotics.

“If a person has penicillin allergy in their medical record, alternative antibiotics are used, which are typically stronger, broader spectrum, and can cause more adverse effects and antibiotic resistance, not to mention [being] more expensive,” Kaplan said.

“There’s a big movement to unlabel people from a diagnosis of penicillin allergy.”

These alternative antibiotics can sometimes be less effective and are considered second-line therapies. This also increases the risk of having illnesses due to infections from bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) or even Clostridium difficile (C. diff).

One study showed that penicillin allergies can cause excess of $1,145 to $4,254 per person for both outpatient and inpatient drug costs as well as inpatient hospitalizations.

There are things people can do to minimize the undesirable side effects of medications. Kaplan said that simple measures, such as taking antibiotics after meals to help decrease nausea and abdominal pain (two of the most common side effects of antibiotics), can help.

The symptoms to be most concerned about are those that occur almost immediately. This includes itchy rashes, shortness of breath, a throat-closing sensation, nausea and vomiting, dizziness, or passing out, Dr. CaJacob said.

If you’re unsure whether you’re allergic to penicillin or not, Kaplan suggests seeing an allergist to be evaluated. Depending on a person’s medical history, allergy testing often includes penicillin skin testing, with results usually available within an hour.

“After testing, far less than 10 percent of people are found to have a true penicillin allergy,” CaJacob added.

Penicillin allergies often subside over time. CaJacob said that although nothing can be done except avoiding penicillin if you’re truly allergic, many people grow out of their allergy at a rate of approximately 10 percent per year. “This means that about half of people will outgrow their allergy five years after the original reaction, and after 10 years over 90 percent of people have outgrown it.”

Although penicillin allergies are commonly reported on medical records, many people aren’t actually allergic to the medication and may have already grown out of the allergy if enough time has passed.

Removing unnecessary allergies from allergy lists in medical records can help not only patients, but also doctors, who as a result will have more options for providing the safest, most effective, and affordable treatment.