Based on the history, oral herpes would present with a history of oral-to-oral contact or oral-to-genital contact with someone with an active herpes infection. Canker sores generally have idiopathic and multifactorial causes such as local trauma, emotional or physiologic stress, allergy or sensitivity, or nutritional deficiencies
Based on the physical exam, besides lack of fluid-filled lesions,
Canker sores occur on non-keratinized oral mucosae such as along the labial or buccal surfaces, soft palate, the floor of the mouth, the ventral or lateral surface of the tongue, tonsillar fauces, free (marginal or unattached) gingiva adjacent to teeth, and alveolar gingiva in the maxillary and mandibular sulci.
ulcerations from herpes simplex virus (HSV) involve the keratinized mucosal surfaces such as the attached gingival and dorsum of the tongue, lips, and hard palate.
Plewa MC, Chatterjee K. Aphthous Stomatitis. [Updated 2020 Jan 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK431059/