So you think you or your child is allergic to penicillin, and maybe you’ve even been told that by a local doctor.


The Centers for Disease Control and Prevention want you to rethink that. According to its fact sheet, 10 percent of Americans think that they are allergic to penicillin, but less than 1 percent actually are.


A 2017 study of children who came into an emergency room found that of the 100 kids whose parents thought they had a penicillin allergy, none of them actually did.


Why would that be?


We asked Alison Humphrey, a local pediatric allergy and immunology specialist at Texas Children’s Hospital, to try to explain what’s going on.


First, you can have a reaction, like a rash, without actually being allergic. A true allergy comes with what’s called an IgE-mediated (Type 1) reaction — that’s a reaction that occurs within an hour of the first time you take the antibiotic. It also might have hives that are what the CDC calls “intensely itchy.” It also will have a localized area of swelling on places like the belly, face, arms or legs, genitals or throat. It also can have wheezing or shortness of breath, and then the ultimate anaphylaxis reaction, which is a severe reaction that can include swelling of the lips, tongue or throat along with trouble breathing.


Even if you have had a reaction like that, the CDC found that about 80 percent of those people outgrow their penicillin reaction after 10 years.


Also, if you’re a parent who believes your child might have the allergy because you do, rethink that. Humphrey says, “It’s not genetic; it’s not passed on.”


Deciding that someone is truly allergic to penicillin when they just have a milder reaction that comes days later or having them believe that they are still allergic when they might have outgrown it can prevent doctors from prescribing a drug that is relatively inexpensive and very effective on a number of diseases or symptoms. It can cause patients to build up resistance to other antibiotics, which then reduces which medications they can use the next time they need an antibiotic or cause them to choose an antibiotic that has worse side effects such as destroying the good bacteria in the stomach. Penicillin also treats a large variety of illnesses, whereas other antibiotics are more specialized, making it more complicated to get the right medication.


And “you are not, in general, increasing rates of antibiotic resistance,” Humphrey says.


To figure out if someone is truly allergic or still allergic, Humphrey will have them come in and do a skin scratch test, introducing a bit of penicillin under the skin to see if a reaction develops. Or she will give a patient a dose of penicillin in the office and watch for a reaction. If you do the test and you have the reaction, the clinic will then treat you for the reaction and advise you to avoid penicillin for another five years.


If nothing happens with either test, you can go ahead use penicillin the next time you have a need for an antibiotic. If you do have a reaction, like a bothersome rash days later, you would just treat the symptoms rather than avoid penicillin all together.


If you are really allergic, Humphrey advises getting a medical alert bracelet noting this allergy because you don’t want to be in the emergency room and be given it as the first line of defense for something.