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Penicillin skin test


Penicillin is a type of medicine called an antibiotic. Doctors give it to treat and prevent infections from bacteria. Many other antibiotics are similar to penicillin, such as amoxicillin and ampicillin. Doctors often prescribe medicines from this important group, but some people are allergic to them. These allergies can be severe in some people, and even cause life-threatening problems.

What is an allergy?

An allergy is an abnormal reaction to something such as dust, pollen, or medicine. Your body’s infection-fighting system, called the “immune system,” makes substances that fight what your body is reacting to. The substances your body makes can cause allergy symptoms. These can include:

  • Bumps on your skin, called hives,
  • Redness, swelling, or itching,
  • Low blood pressure, and
  • Breathing problems.

Allergy symptoms can be mild or severe. For example, mild symptoms can include sneezing and itchy eyes. Severe symptoms can include low blood pressure and breathing problems. These can be very serious.

Why does my child need a penicillin skin test?

A penicillin skin test tells the doctor if your child has a serious allergy to penicillin. About one (1) person in every 100 has a serious penicillin allergy. If your child does, penicillin or similar medicines should not be taken. If they do not have a serious allergy, taking these medicines is safe.

Your child’s doctor, nurse, or pharmacist can tell you if your child needs a penicillin skin test.

How is the test done?

The test has 3 steps. It will stop if any step shows your child has a serious allergy.

  1.  Step 1: Scratch test
    • A nurse puts an allergy-causing substance related to penicillin on your child’s skin. Then, they rub the skin with it and wait 15 minutes.
    • A nurse checks for a positive or negative result after 15 minutes.
  2.  Step 2: Skin test
    • A nurse gives your child 5 small injections (shots) in the top layer of skin. Then, they wait 15 minutes.
    • A nurse checks for a positive or negative result after 15 minutes.
  3. Step 3: Testing by mouth
    • A nurse gives your child a penicillin-type medicine in a pill or liquid. Then, they watch your child for 1 hour (60 minutes).
    • A nurse checks for a positive or negative test for up to 1 hour (60 minutes).

After the test

Your child will have at least one (1) small, red itchy bump on the skin after the test. This looks like a mosquito bite. You can put a cool cloth or cold pack on it to help the itching. The bump goes away in a few hours.

Your child might have more swelling, redness, or a rash after you leave the clinic. This is rare, but it sometimes happens. Please call your child’s doctor, nurse, or pharmacist if it does. If your child has a medical emergency and needs help right away, you should call 911.

If your child’s results are positive

If any of the tests are positive, your child is allergic to penicillin. They will not have any more tests. The St. Jude staff will make a note about the allergy in your child’s medical record. Your child will not get penicillin and similar medicines at St. Jude in the future.

Please tell your child’s other doctors and pharmacies about the allergy. This tells them not to prescribe these medicines for your child.

If your child’s results are negative

If all the tests are negative, it means your child is not allergic to penicillin. They can probably take penicillin and similar medicines. Please tell your child’s other doctors and pharmacies about this. This tells them they can safely prescribe these medicines to your child.

How to get ready for the test

  • Bring a list of all the medicines your child took in the last week (7 days).
  • Tell the person doing the test if your child had a fever or wheezing symptoms in the last 24 hours. “Wheezing” means noisy breathing even when your child is resting.
  • Avoid giving any allergy medicines called “antihistamines” for 72 hours (3 days) before the test. These medicines include:
    • Diphenhydramine (Benadryl®),
    • Cetirizine (Zyrtec®),
    • Cyproheptadine (Periactin®)
    • Promethazine (Phenergan®),
    • Loratadine (Claritin®),
    • and other antihistamine medicines.

These medicines usually say “antihistamine” on the package. Please ask your child’s doctor, nurse, or pharmacist if you have a question about medicines. Be sure to ask them before your child’s test.

What are the side effects of penicillin skin testing?        

Side effects can happen from testing or because your child is allergic to penicillin.

They can be mild, such as:

  • Itching, redness, or a warm feeling – in the area the shot was given,
  • Nausea, vomiting, or changes in how things taste,
  • Pale skin,
  • Sweating,
  • Cough, or
  • Skin rash.

Severe side effects are rare. They can include:

  • Feeling faint or dizzy,
  • Breathing problems,
  • Fast heart rate,
  • Low blood pressure, and
  • Swelling of the tongue or throat. This can keep your child from breathing.

Your child’s St. Jude team will give medicine right away if they notice a side effect or allergic reaction.


If you have questions about penicillin skin testing, please ask your child’s doctor or nurse. You may also call St. Jude at 901-595-3300 and ask to speak with someone in your child’s primary clinic.


This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.

St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.

ATTENTION: If you speak another language, assistance services, free of charge, are available to you. Call 1-866-278-5833 (TTY: 1-901-595-1040).

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