Are canker sores caused by the herpes virus?

Are Canker Sores Caused by Herpes?

No, canker sores (aphthous stomatitis) are NOT caused by the herpes virus and are a completely different condition from cold sores (herpes labialis), which ARE caused by herpes simplex virus. This is a critical distinction that affects diagnosis, treatment, and patient counseling.

Key Differences Between Canker Sores and Cold Sores

Canker Sores (Aphthous Stomatitis)

• Not caused by herpes virus - oral acyclovir (an antiviral medication for herpes) has been proven completely ineffective for preventing or treating canker sores 1
• Appear inside the mouth on non-keratinized mucosa (inner cheeks, tongue, soft palate) 2
• Are not contagious and not sexually transmitted 1
• Present as painful ulcers without preceding vesicles 2

Cold Sores (Herpes Labialis)

• Caused by HSV-1 (herpes simplex virus type 1) and affect 20-40% of adults 3
• Appear outside the mouth on the lips, around the mouth, and on keratinized skin 4
• Are highly contagious and can be transmitted through direct contact 4
• Progress through distinct stages: prodrome, vesicles, pustulation, ulceration, and scabbing 3
• Respond to antiviral therapy (valacyclovir, famciclovir, acyclovir) 5, 3

Clinical Evidence Supporting This Distinction

The definitive study demonstrating that canker sores are not herpes: A double-blind trial of 44 patients receiving oral acyclovir (the standard antiviral for herpes) for one year showed no effect whatsoever on aphthous stomatitis recurrences - neither the frequency nor duration of canker sore attacks changed 1. This proves canker sores have a completely different etiology from herpes infections.

Common Pitfall to Avoid

Do not confuse intraoral herpes lesions with canker sores. While herpes typically causes lesions outside the mouth, HSV can occasionally cause ulcerative lesions inside the oral cavity, particularly in immunocompromised patients 6. However, these are still herpes infections (caused by HSV), not aphthous stomatitis. The key distinguishing features:

• Herpes intraoral lesions: Begin as vesicles, occur on keratinized tissue (hard palate, gingiva), associated with systemic symptoms in primary infection, and respond to antivirals 4, 6
• True canker sores: No vesicular stage, occur on non-keratinized mucosa, no systemic symptoms, and do not respond to antivirals 1, 2

Treatment Implications

Since canker sores are not caused by herpes:

• Antiviral medications are completely ineffective and should not be prescribed 1
• Treatment focuses on symptomatic relief with topical analgesics and barrier-forming agents 2
• Patients should be counseled that canker sores are not contagious and not related to sexually transmitted infections 1