Penicillin is one of the most widely prescribed antibiotics today. This family of medicines can treat bacterial infections like strep throat, pneumonia, and sinus and urinary infections. But penicillin can be dangerous for people who are allergic to it.

About 1 in 10 of all U.S. patients report a penicillin allergy, according to the Centers for Disease Control & Prevention. However, up to 90% of these patients don’t have a true allergy. And avoiding penicillin unnecessarily has its disadvantages. Summit Health allergist and immunologist Gary Pien, MD, PhD, answers questions about penicillin allergy and how to find out if you are ­ – or still are – allergic.

What can happen if you’re allergic to penicillin?

An allergy is the body’s overreaction to normally harmless substances. Certain medicines are among the most common substances to cause allergic reactions. A penicillin allergy can trigger:

• Skin reactions such as itching, rashes, hives, and swelling
• Respiratory symptoms such as wheezing and shortness of breath

Less commonly, a penicillin allergy can cause a severe reaction called anaphylaxis. Symptoms of anaphylaxis can be life-threatening and include difficulty breathing, a dangerous drop in blood pressure, and loss of consciousness.

Most allergic reactions to penicillin happen within an hour of taking it. While anyone can have a penicillin allergy, your risk of allergy may be higher if you:

• Have a family history of allergies
• Previously experienced a drug allergy
• Have had frequent exposure to penicillin

Why do some people report a penicillin allergy when they don’t have one?

Someone may believe they have a penicillin allergy for a few reasons:

• They experience a side effect of the drug, such as nausea or headache, that’s mislabeled as an allergic reaction.
• Signs and symptoms of an underlying bacterial or viral infection can also be mistaken as a penicillin allergy.
• Reliable penicillin allergy tests weren’t available until more recently.

In addition, most people outgrow their allergy. Between 80% and 100% of patients ultimately test negative for penicillin allergy 10 years after their last positive test, according to the National Institutes of Health.

Is there a downside to avoiding penicillin if I’m not allergic to it?

Having an unconfirmed penicillin allergy can negatively impact your medical care. By avoiding penicillin unnecessarily, patients often receive alternative antibiotics that:

• Are stronger and may have a higher risk of side effects
• Increase the risk of developing antibiotic resistance
• Are associated with higher healthcare costs

How do I find out if I’m allergic to penicillin – or still allergic?

Talk to your provider if you’re unsure whether you have a true penicillin allergy. Better yet, ask to see an allergist for penicillin allergy testing. During your initial consultation, your allergist will determine the most appropriate testing strategy. An oral drug challenge may eventually be conducted at some point to confirm that you can now tolerate penicillin.

Diagnosing a penicillin allergy may involve skin testing and an oral drug challenge. For a skin test, your provider will either apply drops of penicillin on the skin and prick the surface or inject a small, diluted amount just under the skin. If an itchy bump appears, the test is positive, and you likely have a penicillin allergy.

If the skin test is negative, your provider may follow with an oral drug challenge. For this test, you take penicillin by mouth under observation to confirm you can safely tolerate it.

Blood tests can also diagnose a penicillin allergy.

What are my options if I have a true penicillin allergy?

Your provider will need to prescribe other antibiotics if you’re allergic to penicillin. But if you get an infection that only penicillin will treat, your provider may recommend desensitization.

Desensitization is a procedure that starts with tiny doses of penicillin, increasing them over time up to normal dosage under careful monitoring. Because desensitization is a temporary approach, the process must be repeated if penicillin is necessary for future treatment.

Summit Health can help.  

If you think you may have a penicillin allergy, make an appointment with an allergist at Summit Health. Tests are available and can determine if you still have an allergy.