During canal irrigation with chlorhexidine, a patient develops sudden discomfort and hives on the neck. What is the diagnosis?

Correct answer: D. Anaphylaxis / anaphylactoid reaction to chlorhexidine

• A. A hypochlorite accident causes immediate severe pain and rapid facial swelling/ecchymosis in the local region — and the irrigant here was chlorhexidine.
• B. A chemical burn produces localized pain and tissue necrosis, not distant urticaria on the neck.
• C. Syncope produces pallor, bradycardia and loss of consciousness, without hives.
• D. Correct. Chlorhexidine is an increasingly recognized cause of perioperative anaphylaxis. Urticaria appearing rapidly during exposure signals systemic mast-cell activation — stop the procedure, assess the airway, and be ready with epinephrine.