What adverse reaction can penicillin (PCN) cause?

Penicillin can indeed cause skin reactions, one of the most common being a rash. This occurs as a result of the body's immune response to the medication. The rash can present in various forms, such as urticaria (hives) or a maculopapular exanthem, and is often a sign of an allergic reaction. Allergic reactions can vary in severity, and while some may be mild, they can also lead to more serious conditions in certain individuals.

While respiratory distress, vomiting, and headache can occur in some patients, these symptoms are less directly associated or common as side effects of penicillin compared to skin reactions like a rash. For instance, respiratory distress typically relates to severe allergic reactions such as anaphylaxis, which, while life-threatening, is not as frequently observed as rashes. Vomiting and headache may be seen with various medications but are not specific or primary adverse reactions of penicillin itself. Hence, the rash is the most characteristic and prominent adverse reaction associated with penicillin use.