Are you allergic to penicillin? If so, are you sure about that?

It’s surprisingly common for people to wrongly think they have a penicillin allergy — and that misconception can be dangerous for their health.

Ten percent of all patients in the United States claim to have a penicillin allergy. Of those people, 90 percent are not truly allergic and can tolerate the drug. That means millions of people take alternative antibiotics, which are more expensive and can put their health and potentially the health of others at risk. The solution is a simple allergy test.

A study in the British Medical Journal (BMJ) looked at six years’ worth of medical records for patients in the United Kingdom and found that those with a penicillin allergy had an almost 70 percent greater chance of acquiring a methicillin-resistant Staphylococcus aureus (MRSA) infection and a 26 percent increased risk of Clostridium difficile-related colitis (C. diff.). MRSA and C. diff. are major health risks worldwide. The study compared adults with a known penicillin allergy to similar people without a known penicillin allergy.