**Core Concept**
Penicillin allergy is a form of hypersensitivity reaction, specifically an IgE-mediated allergic response. This occurs when the body produces antibodies against the penicillin molecule, leading to the release of histamine and other chemical mediators, resulting in symptoms such as hives, itching, and anaphylaxis.

**Why the Correct Answer is Right**
The correct answer is Type I hypersensitivity reaction, also known as immediate hypersensitivity or anaphylactic reaction. This type of reaction occurs when IgE antibodies bind to mast cells and basophils, leading to the release of histamine and other chemical mediators. In the context of penicillin allergy, this reaction is mediated by IgE antibodies against the penicillin molecule, resulting in anaphylaxis or other allergic symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Type II hypersensitivity reaction is incorrect because it involves IgG or IgM antibodies against cell surface antigens or matrix proteins, leading to cell destruction or activation, which is not the primary mechanism of penicillin allergy.
**Option B:** Type III hypersensitivity reaction is incorrect because it involves immune complex formation and deposition, leading to inflammation and tissue damage, which is not the primary mechanism of penicillin allergy.
**Option C:** Type IV hypersensitivity reaction is incorrect because it involves T-cell mediated immune response, leading to delayed hypersensitivity reactions, such as contact dermatitis or tuberculin reaction, which is not the primary mechanism of penicillin allergy.

**Clinical Pearl / High-Yield Fact**
A patient with a history of penicillin allergy should be evaluated for a possible anaphylactic reaction, and alternative antibiotics should be considered to avoid a severe allergic reaction.

**Correct Answer:** C. Type I