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Outgrowing Penicillin Allergy

Penicillin and Amoxicillin are excellent antibiotics that have been widely used for decades to treat bacterial infections.  Although Penicillin was observed to kill bacteria in 1928, its clinical use for treating infections started in the 1940’s.  Current preparations of penicillin are synthetic and not derived from the fungus Penicillium notatum.

Unfortunately, some individuals will develop an allergy to penicillin with symptoms of hives, wheezing or even anaphylaxis.  Allergy to penicillin and related antibiotics is the most commonly reported drug allergy in the U.S.   It is estimated that 10% of the U.S. population self-report as being allergic to penicillin; however, only 1% have a true penicillin allergy.  In addition, it is not widely known that many people will “outgrow” their penicillin allergy, but it takes time.  After 10 years of avoidance of penicillin, about 50% of persons will outgrow this allergy; after 15 years of avoidance, nearly 75% of persons who previously had an allergic reaction will no longer have penicillin allergy.   This is especially true for those persons who had milder reactions such as rashes.

Why is this important?  If you have been labeled as allergic to penicillin, then alternative antibiotics will be prescribed.  Frequently these second-line antibiotics are more expensive and carry the risk of more side effects.  The continued extensive use of broad-spectrum antibiotics may also contribute to drug-resistant bacteria.

Good news!  There is an FDA-approved commercial extract of penicillin for skin testing called Pre-Pen.® Skin testing with this extract alone can be very helpful (90%) in determining if a person has outgrown their allergy to penicillin especially if the skin test is negative.  When a skin test with Penicillin G is also included, then the chance of identifying if penicillin allergy has resolved is almost 97%.

If it has been 1) years since you had an allergic reaction to penicillin; 2) so long ago that you don’t recall the reaction; or 3) your mother told you to “never have penicillin again” because you had a reaction as an infant or child, know that you very well may not be allergic anymore.

See us at Family Allergy & Asthma Care of Montana—we can test you for penicillin allergy!

This educational information does not take the place of your physician’s advice.


  1. KeoniKeoni08-30-2014

    So I was 2 years old and I was given penicillin. I had a allergic reaction to it. But now I am turning 19 and haven’t been given penicillin since then. Could I have outgrown it by now? I am going into the army. So could I have outgrown it?

    Yes, there is a chance that the penicillin allergy has resolved. See a board-certified allergist and have testing performed.

  2. AmyAmy09-07-2016

    I had a severe allergic reaction to these when I was a small child, being unable to breath and such. I also suffered from blistering from clindamycin at that age. However it has been 17 years and I have had neither of them since. Is there a chance I could have outgrown these allergies in this time frame?

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