Physicians used to assume a child who developed a mild drug-related rash could have a more serious reaction in the future. But research conducted over the last 10 years has shown that isnt true. Our understanding has really changed for the better, said Dr. Stukus. But it can be quite confusing for parents because what they were told a few years ago or even what they themselves were told as children may be very different.

True allergic reactions, which occur when the bodys immune system overreacts, almost always come on suddenly within minutes to a few hours of taking the drug. Symptoms commonly include hives, itchy eyes and swelling in the lips, tongue or face. In some cases, the allergy can cause vomiting and diarrhea. Rarely, penicillin allergies lead to anaphylaxis, a life-threatening reaction that affects the entire body. Even more rarely, a child will develop severe symptoms such as a high fever or blistered, peeling skin days or even weeks after taking the drug.

Dr. Norton said parents should call their doctor if their child experiences any new symptoms while taking a drug. Take photos and write down pertinent details. Knowing what happens when a child has a reaction is key to figuring out how to manage these kids, so the parent really is an important part of this, she said.

If a health care provider is concerned about the symptoms, or just unsure, they may stop the penicillin and prescribe a different antibiotic, Dr. Norton said. If that happens, be sure to follow up with your physician or allergy specialist to figure out if your child is really allergic.

Allergy testing should be done in a doctors office or clinic where they have treatment on hand in case symptoms occur.

It can involve a lot of waiting to see if anything happens, so bring a quiet activity to pass the time. Most kids undergo an oral challenge where they are given a small amount of the drug, then if theres no reaction, the rest of the dose. If nothing happens after an hour or so, youre good to go.

If your child has a history of severe symptoms such as swelling, or shortness of breath or a rapid onset of hives, you will need to consult with an allergy specialist for a skin test. That involves first pricking the skin with an allergen, and if that doesnt cause a red bump to form, using a small needle to place more of the allergen under the skin. (The procedure is bloodless and less painful than it sounds.) If theres no reaction at the testing sites, the doctor will do an oral challenge to confirm your child isnt allergic.

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Your Kid Probably Doesnt Have a Penicillin Allergy - The New York Times