Think You’re Allergic to Penicillin? There’s a Good Chance You’re Not! By Albert S Hartel MD
September 28, 2026 2:43 pm
Think You’re Allergic to Penicillin? There’s a Good Chance You’re Not!
By Albert S Hartel MD
Allergy Asthma Immunology Rochester
September 28 is National Penicillin Allergy Day, marking the anniversary of Alexander Fleming’s discovery of penicillin in 1928. Nearly a century later, penicillin and related antibiotics remain among the safest and most effective treatments for many infections. Yet about 1 in 10 patients carry a “penicillin allergy” label in their medical record — and more than 90% of those patients are not truly allergic.
That mismatch matters. An inaccurate allergy label often leads doctors to choose broader-spectrum or less effective antibiotics. Over time, that can mean more side effects, higher rates of C. difficile and drug-resistant infections, longer hospital stays, and higher costs. For many people, the label was added years or decades ago after a childhood rash, nausea, or a reaction that was never clearly distinguished from the infection being treated.
Why so many labels are wrong
True penicillin allergy is much less common than the chart suggests. Side effects such as upset stomach or headache are frequently recorded as allergies. Viral rashes in children are often mistaken for drug reactions. Even when a genuine allergic reaction did occur, most people lose that sensitivity over time. After about 10 years, more than 90% of previously allergic patients no longer react.
How allergists evaluate penicillin allergy
A board-certified allergist starts with a careful history, and proceed to skin testing with possible need for oral challenge to fully clarify. A negative evaluation means penicillin-class antibiotics can be used safely again. A positive test confirms the allergy so future treatment can be planned accordingly.
Who should consider testing
Anyone with a penicillin allergy on their record can benefit from a review — especially before surgery, dental work, pregnancy, or treatment of a serious infection. Clearing an incorrect label is one of the most practical steps a patient can take for better care. If you have been told you are allergic to penicillin, talk with a board-certified allergist about whether testing is right for you. For many people, the answer is that they can use penicillin safely after all.