NEW YORK (CBSNewYork) – Are you allergic to penicillin? Millions of people believe they are, but it turns out that many aren’t allergic at all.

CBS2’s Dr. Max Gomez spoke to allergists about how patients can find out if they should actually avoid the antibiotic.

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Many believe that, even if you’re not really allergic to penicillin, the worst that could happen by avoiding it is receiving a different antibiotic.

The problem with that is those other antibiotics may cause more side effects, not work as well, and are certainly more expensive.

Carolyn and Ron Staszewski both remember how long it’s been since they first thought they were allergic to penicillin.

For Ron, it was 50 years ago when he got an injection in the Army.

For Carolyn, it was when she had their first child.

“I broke out in a rash all over and they said oh never again, you can’t take penicillin,” Carolyn said.

They’re part of the 10 percent of the population who list themselves as allergic to penicillin however, only about one percent are actually allergic.

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“When we’re children and we have this added to our medical record then over time as we get repeated infections we don’t ever address the issue again,” Dr. Kim Blumenthal, an allergist at Mass General Hospital said.

That’s how Claire Branman came to think she was allergic. Then an alternative antibiotic for a minor dental procedure led to much bigger health problems.

“It was a nightmare and I actually ended up having my stomach kind of messed up for a few years since then,” Branman said.

A penicillin allergy prevents patients from taking any form of the pencillin, including amoxicillin and augmentin.

Now allergists at Mass General Hospital in Boston have developed an app to help doctors quickly identify patients who should get tested for penicillin allergy.

A doctor and patient look over the penicillin allergy app. (Credit: CBS2)

“It helps the doctor or the nurse ask more detailed questions that are usually allergy specialist knowledge,” Dr. Blumenthal explained.

It’s a simple skin test, like checking for pollen or mold allergies. It turned out Claire is not allergic, which could make a big difference next time she needs antibiotics.

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“Sinus infections, ear infections, pneumonia, bladder infections, skin infections. Anything you can name, usually penicillin is going to be the preferred option,” Dr. John Kelly said.