Penicillin allergy is the most commonly reported antibiotic allergy in the United States. Although many patients report a penicillin allergy, studies show that 90% of those patients are not truly allergic. This majority of patients who are not, in fact, allergic, but report that they are, require alternative therapies which are often more expensive and less-ideal choices to treat their infection.

Many patients report they had a rash when given penicillin as a child but have no other details and avoided it ever since. Some patients were told their parents were allergic to penicillin and were never even exposed to it themselves as a result.

Penicillin skin testing is an easy way to find out, for sure, if a patient is penicillin allergic or not. The skin test is then followed up with an oral challenge (on a separate day) in which a patient is given a full dose of amoxicillin to rule out a clinical reaction.