How does penicillin trigger an immune response in some people?

Penicillin can trigger an immune response in some individuals due to an allergic reaction, where the immune system mistakenly identifies the drug as a harmful substance. This response often occurs when penicillin binds to proteins in the body, forming new structures that the immune system recognizes as foreign. In sensitized individuals, subsequent exposure can lead to symptoms ranging from mild rashes to severe anaphylaxis, as the immune system activates and releases histamines and other chemicals. Genetic factors and previous exposure to penicillin can influence the likelihood of developing this allergic response.