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Think You Have a Penicillin Allergy? Maybe Not, According to an Expert

A lot of people think they are allergic to penicillin, but they aren’t. According to the Centers for Disease Control and Prevention (CDC), about 10 percent of people in the United States believe they have a penicillin allergy. But less than 1 percent are likely truly allergic.

Why do so many people mistakenly believe they have a penicillin allergy? They may have assumed they were allergic because one of their parents had a penicillin allergy. They could have developed a rash after a course of penicillin as a child and been labeled allergic. Or they might have had an allergy that faded away over time.

If you believe you’re allergic, you might think that you should avoid penicillin to be on the safe side. After all, there are a lot of other antibiotics you could turn to if you need treatment. But knowing whether you're allergic matters.

The CDC reports that the broad-spectrum antibiotics used as an alternative to penicillin can be less effective, raise healthcare costs and increase the risk of antibiotic resistance.

And if you are indeed allergic to penicillin, it’s not as simple as avoiding penicillin. You would then need to avoid a group of antibiotics in the same drug family, including amoxicillin (Augmentin), said Puneet Shroff, MD, an allergist at Banner – University Medical Center Tucson. “These are antibiotics that are the first-line treatment for many conditions from childhood through later in life. The ability to have the option for a drug in this family if needed for medical treatment is imperative.” Therefore, if you have been labeled with a penicillin allergy, confirming whether you are allergic is an important next step.

How to find out if you have a penicillin allergy

If you believe you have a penicillin allergy, an allergist or immunologist can consult with you to see if it makes sense to be tested. “There’s a very sensitive skin test for penicillin that’s available now,” Dr. Shroff said. “These tests are done under a trained eye that understands how to perform and interpret them. Overall, the testing is very safe and are routinely done in many allergist’s offices. Very rarely, allergic reactions occur, which is another reason for these tests to be done under an allergist’s supervision.”

To start, your doctor will likely ask you what you remember about the history of your suspected penicillin allergy:

  • When did a reaction take place?
  • What happened, exactly? What symptoms can you report?
  • What else was going on? Why were you being treated with penicillin?

Nonallergic reactions to antibiotics, including penicillin, can also occur and should be discussed with your doctor during consultation. However, if your answers indicate you should be tested, your doctor will introduce a small amount of penicillin to your skin through a scratch or prick, usually on your forearm or back. After 15 or 20 minutes, your doctor can check for any swelling, redness, irritation or itching as those could be signs of an allergic response.

If that test is negative or inconclusive, your doctor can perform a second test that goes a little further underneath the skin, again on the arm or back. Again, your doctor will assess your skin in 15 to 20 minutes.

If the skin tests don’t show signs of a penicillin allergy, you may be eligible to move on to an oral challenge. “That’s the gold standard for eliminating or confirming a penicillin allergy,” Dr. Shroff said. In this challenge, you take several small doses of penicillin by mouth, and you are monitored for the next hour or two for any reaction. You can usually do the oral test in the same doctor’s visit as the skin tests.

If these tests don’t show any sign of a penicillin allergy, your doctor will likely determine that you don’t have one and recommend taking it off your medical record. That way, if you need treatment with penicillin or a related drug, you’ll be able to take it.

If you’ve been told you have a penicillin allergy, it’s a good idea to look into testing when you’re healthy. “Once you’re sick and might need a penicillin product, testing might not be appropriate,” Dr. Shroff said.

The bottom line

Many people believe they have a penicillin allergy, but only a small number are truly allergic. Testing can help you find out if you have one. If you don’t, you’ll be able to take penicillin if you need it to help control an infection.

If you need to connect with an allergist or immunologist to evaluate your possible penicillin allergy, talk to your primary care provider or reach out to Banner Health to find an expert.

These articles can help you learn more about common allergies:

Allergy and Immunology Infectious Disease