A 17-year-old otherwise healthy male under significant academic stress presents with a painful lesion on the hard palate that appeared suddenly. What is the most likely diagnosis?

Correct answer: A. Recurrent intraoral herpes simplex (herpes on keratinized mucosa)

• A. CORRECT. Recurrent herpes simplex virus (HSV-1) reactivation in the oral cavity is triggered by stress, immunosuppression, UV exposure, or trauma. Recurrent intraoral herpes classically appears on KERATINIZED, ATTACHED mucosa — specifically the hard palate and attached gingiva. The lesions begin as vesicles that rapidly rupture into clusters of small ulcers. The hard palate location + stress trigger = recurrent herpes.
• B. Aphthous ulcers (canker sores) classically occur on NON-KERATINIZED, MOVABLE mucosa (buccal and labial mucosa, floor of mouth, ventral tongue) — NOT on the hard palate, which is keratinized. This is the key clinical distinction.
• C. VZV reactivation (shingles) is uncommon in a healthy 17-year-old, follows a dermatomal distribution, and would not be unilateral to the hard palate in isolation.
• D. Primary herpetic gingivostomatitis occurs in initial infection (usually children 1–5 years), causing widespread vesicles/ulcers on all mucosal types, fever, lymphadenopathy, and malaise. The 17-year-old's localized palatal lesion without systemic symptoms suggests recurrence.