Canker Sores vs. Cold Sores vs. Other Oral Blisters: Differential Guide

Canker Sores (Aphthous Ulcers)

• Inside mouth (non-keratinized mucosa)
• Round/oval, yellow-white center, red halo
• Not contagious
• Triggers: stress, trauma, foods, SLS, deficiencies, immune
• Heal 7–14 days

Cold Sores (Herpes Labialis / HSV-1)

• Lip/vermilion border (keratinized)
• Vesicles → crust
• Highly contagious
• Recurrent (triggers: UV, stress, illness)
• Prodrome: tingling/burning

Other Causes of Oral Blisters/Ulcers

• Stomatitis: General inflammation — infectious (herpetic, coxsackie), allergic, autoimmune (lichen planus, pemphigus), chemo/radiation
• Hand-Foot-Mouth (Coxsackie A16 / Enterovirus 71): Kids; oral vesicles + palm/sole rash + fever
• Allergic contact: Toothpaste (SLS, flavors), foods, dental materials
• Erythema multiforme: Target lesions, often HSV-triggered

When to See Clinician

• >2 weeks, recurrent (>6/yr), large (>1 cm), systemic symptoms, immunosuppressed