If you are one of the millions of Americans who was told as a child that you were allergic to penicillin – and haven’t used the antibiotic since – it’s possible you may have outgrown the allergy, according to a study by the American Academy of Allergy, Asthma and Immunology.

Giselle Mosnaim, MD, Allergy & Immunology at NorthShore, said about 50 percent of penicillin allergic patients lose their sensitivity five years after the last reaction, and about 80 percent of penicillin allergic patients lose their sensitivity 10 years after the last reaction. Re-evaluation is often recommended because patients may have negative skin test results to penicillin, and safely tolerate penicillin, even if they had serious reactions in the past.

This is exciting news but it doesn’t mean you can declare yourself or your children cured. Dr. Mosnaim answers questions about penicillin allergy:

Other drugs are effective. Why is it important to find out if someone is still allergic to penicillin?

The use of alternatives to penicillin results in many disadvantages. Alternative antibiotics may be more expensive, cause more side effects, and in some instances, be less effective. In addition, use of alternative broad spectrum antibiotics contributes to the development and spread of antibiotic-resistant bacteria.

How much time has to pass since the initial reaction before someone can check to see if they still are allergic?

It is standard to allow at least four weeks since the initial reaction. We do not perform the testing in the weeks immediately after the allergic reaction because the reaction causes massive activation of the immune system. In other words, the immune system may be hypo-reactive for a few weeks after a severe allergic reaction and need some time to recover before it is advisable to proceed with testing.

What is the safe way for someone to find out if he or she is still allergic?

Penicillin skin testing performed by specifically trained personnel – usually allergy specialists – is recommended. Allergists receive specialized training in performing penicillin skin testing and oral challenges. Penicillin skin testing rarely leads to serious reactions, but it should always take place in a setting and by personnel prepared to treat possible allergic reactions.

Are you allergic to penicillin? When was the last time that you were tested for allergies?