-- Question: Why do I get hives when I take Penicillin?
Answer: Among the many causes of hives are allergic reactions to possibly foods, and/or drugs. The most common drug related to allergies is penicillin.
In this case, there are cells in the skin that carry the itch chemical histamine and these cells can react to the penicillin as if it is a foreign or invading substance.
Therefore, if you are penicillin allergic, you may find that when you eat penicillin or take penicillin on the very first occasion, you may suffer these itchy red bumps.