While 10% of people in the United States report being allergic to penicillin, 9 in 10 are not. However, this can be difficult to scratch from medical records.

Share on Pinterest New research suggests that many adults who used to be allergic to penicillin in their childhood may have outgrown the allergy.

So concludes one of three studies presented at a scientific meeting in Houston, TX, shedding fresh light on the antibiotic.

Alexander Fleming discovered penicillin by chance in 1928 when he noticed that penicillin fungus was a potent antibacterial. Doctors first used this now common antibiotic as medicine in the 1940s, finally giving doctors a weapon against deadly infections.

Penicillin went into mass production in the U.S. during World War II, proving its worth on the battlefield where, until then, infection had caused more deaths than war wounds. Today, doctors use this antibiotic to treat a wide range of infections.

However, if an adult or child has ever had a reaction to penicillin, and a doctor has told them that they are allergic to it, the chances are that this “fact” is still on their medical records.

So say researchers who have found that 9 in 10 people in the U.S. who think that they are allergic have outgrown the allergy or were never allergic in the first place.

The researchers add that even when people test negative to a penicillin allergy at a later date, the allergy often remains on their medical and pharmacy charts.

“Our study found that of the 52 patients who tested negative to penicillin and were interviewed, 98% understood they were not allergic to penicillin,” says lead author, Dr. Sonam Sani, an allergist, immunologist, and fellow of the American College of Allergy, Asthma, and Immunology (ACAAI).

“Of those, 29% still had a penicillin allergy label in their electronic medical record, and 24% still carried the label in their pharmacy records.”

The study was one of three into penicillin allergy presented at the ACAAI Annual Scientific Meeting in Houston. The other two examined gender and penicillin allergy, and childhood testing of the allergy.