Which local anesthetic option has the highest incidence of allergic reactions?

• A. Amide local anesthetics
• B. Ester local anesthetics (e.g., benzocaine)
• C. Cocaine
• D. Procaine

Answer: (B)

Allergic reactions to local anesthetics are more common with ester-type agents because they are metabolized to para-aminobenzoic acid (PABA), a substance that many people are sensitized to. This makes esters the class with the higher incidence of true hypersensitivity. Benzocaine, a topical ester, is a classic example that can trigger allergic contact dermatitis, so ester-type agents are more likely to provoke an allergy than amide-type agents. Amide local anesthetics (like lidocaine, mepivacaine) are metabolized differently and are much less likely to cause true allergies, with most adverse reactions due to toxicity or other nonimmune factors rather than IgE-mediated allergy. Cocaine and procaine are esters as well, but in modern practice, the established pattern is that esters carry the higher allergy risk, particularly benzocaine. If a patient has a known ester allergy, choosing an amide alternative reduces the risk.