Fewer than 5 percent, potentially even fewer than 1% of people with a history of a penicillin allergy are truly allergic.
It is the most commonly reported drug allergy with up to 20% of the population labeled with it. These labels are often acquired in childhood where symptoms of an allergic response are confused with symptoms of viral or bacterial illnesses. And for those with true penicillin allergies, most people lose their sensitivity over time.
People with penicillin allergy labels will get treated with more broad spectrum antibiotics that may not work as well. For a number of diseases, penicillin class antibiotics are the first line therapy. These individuals have higher rates of MRSA and C. difficile.
For delabeling, not everyone will need a skin test. Some may be able to do amoxicillin challenges under medical supervision to rule out the allergy.
Every year about ~10% of people with the allergy will lose their sensitivity to it.
Here is a study discussing this: