Most people aren’t really allergic to penicillin. More doctors are doing tests to confirm it.

The vast majority of people who think they have a penicillin allergy don’t have it anymore — or never did, doctors say. Now there’s a trend toward “delabeling” those allergies.

A growing number of allergists and public health officials nationwide are pushing to prove that the majority of people who believe they have a penicillin allergy are not, in fact, allergic to the antibiotic — and can use it safely.

The so-called delabeling of penicillin allergies, doctors say, would have major health impacts: faster and more effective treatments for people who have spent their lives avoiding penicillin and related drugs, including amoxicillin, as well as the opportunity to drive down rising antibiotic resistance.

“There is an evolution going on in that all of us are moving from a reactive approach to penicillin allergies to a proactive approach,” said Dr. Cosby Stone, an assistant professor of allergy and immunology at Vanderbilt University Medical Center in Nashville, Tennessee. “That is to say to patients, ‘I think I should test this allergy for you because I think it’s going to cause you a problem, either now or in the future.'”

About 10% of the U.S. population report having a penicillin allergy, according to the Centers for Disease Control and Prevention. In most of those cases, people had long been told they were allergic to penicillin — usually after developing a rash within several days of taking the antibiotic as a baby or toddler.

Other folks just assumed they had an allergy because a sibling or other family member did.

But the CDC says that less than 1% are truly allergic.

“Some of the things that we thought were allergies just aren’t,” Stone said. “The other thing is that even true allergies fade over time. People grow out of them.”

Stone is leading efforts at Vanderbilt to test patients whose charts say they have a penicillin allergy. People are given a small dose of the antibiotic in a controlled environment and monitored for any reaction.

“We have to test 100 people in order to find one” who reacts, Stone said.

While some of those reactions can be severe, most are not. People may develop a rash, diarrhea or feel nauseated.

“Those are just side effects” of the drug, said Dr. Gerald Volcheck, chair of allergic diseases at the Mayo Clinic in Rochester, Minnesota.

Volcheck said that testing people for true penicillin allergies has grown in recent years. “There really seems to be a nationwide push for this delabeling.”

Though there is no national guidance for penicillin delabeling, the CDC has been following the efforts closely and encourages people to seek out testing.

“Removing a false allergy opens up the options for treatment for patients and results in less use of antibiotics that contribute more to antimicrobial resistance,” Melinda Neuhauser, a pharmacist and acute care lead for the CDC’s Office of Antibiotic Stewardship, said in an email.

Doctors must find other antibiotic options when treating bacterial infections in patients with penicillin allergies. But those drugs don’t always work well.

“We know that patients are getting the wrong antibiotics,” Stone said.

Patients who can’t be given penicillin are often given broad-spectrum antibiotics that may not work as well and should be saved as a last resort for the most severe bacterial infections.

Patients may need to be on those other antibiotics longer. Because they’re less effective, it gives bacteria a chance to grow stronger and evolve more ways to resist the drugs that do work against them.