Penicillin is a commonly used antibiotic that treats many different bacterial infections.  Approximately 10% of the population has been labeled with a penicillin allergy. Out of the 10% labeled with a penicillin allergy, 90% do not have a true allergy to penicillin. A penicillin allergy may be misdiagnosed due to a childhood illness that causes symptoms similar to a drug reaction or symptoms that were a side effect rather than an allergic reaction.  Many adults that have been diagnosed with a penicillin allergy may lose their sensitivity over a 10 year span. Certain people were told as children that they had an allergy to penicillin but cannot recall which type of reaction they experienced or they were told to avoid it because other family members have a penicillin allergy.

A true penicillin allergy is IgE mediated and usually occurs after a subsequent course of penicillin ingestion. This allergic reaction occurs when preformed IgE antibodies react with penicillin causing the release of histamine and other mediators from mast cells which in turn can cause a decrease in blood pressure, difficulty breathing, swelling of lips/tongue, and hives amongst other symptoms.  These symptoms are a sign of a severe allergic reaction and you should immediately seek medical attention if you experience any of them. Some common non-allergic adverse reactions are upset stomach, diarrhea, or rashes.

If you have had a reaction and are unsure if it was due to penicillin ingestion consult with an allergist/immunologist about your history. If you are unsure, then penicillin allergy skin testing may be an option for you.  Penicillin allergy skin testing is a procedure performed to diagnose a true penicillin allergy.  The test is performed in an allergy office and usually takes 2-3 hours.  Penicillin skin testing consists of a skin prick and intradermal test with 2 different forms of penicillin (penicillin G and benzylpenicilloyl polylysine).  If the test is negative then an oral challenge using a penicillin medication may be performed in the office followed by an observation period.  A positive skin test will become red and itchy at the site where the medications are applied. If the skin test is positive penicillin medications will need to be avoided and you may require a different antibiotic to treat bacterial infections.