Differentiating Canker Sores from Oral Herpes.

Of all of the different types of mouth ulcers that are frequently mistaken for canker sores, the most common one is the recurring intraoral herpes lesion. (The term "intraoral" here simply means that it's "in the mouth.")

There's no reason for this confusion. There are some very distinct differences between the two and they are easy to identify. They are:

[Use this link if you're more interested in simply how to identify canker sores. Or if you want information about cold sore identification (another type of herpes lesion) use this link.]

The differences are:

A) They each form in different locations.

1) Oral herpes:

These lesions form on firmly attached, keratinized tissues (skin). This includes:

a) Attached gingiva (the gum tissue that surrounds teeth).

b) The hard palate.

Diagram showing where aphthous ulcers and oral herpes usually form.

The lesions form in different locations.

2) Canker sores:

In comparison, these sores form on loose, non-keratinized tissues of the mouth.

a) The inside lining of the cheeks or lips.

b) The tip or underside of the tongue.

c) The floor of the mouth.

d) In the back of the mouth near the tonsils.

e) The soft palate.

B) In their early stages, they look different.

1) Oral herpes:

These sores first appear as multiple, tiny vesicles (fluid-filled elevations, blisters) having a diameter on the order of 1/25 th of an inch (1mm). (In our picture below, you can actually see a vesicle in the lower right corner that hasn't yet burst.)

2) Canker sores:

Typically first appear as a reddened raised area that ultimately forms into a sore that may become as large as 1/4 of an inch.

Pictures showing the difference between oral herpes and aphthous ulcers.

The shape of the lesions is entirely different.

C) Ulcer shape.

1) Oral herpes:

Ruptured herpes vesicles coalesce to form a larger sore. The borders of the combined ulceration usually have a scalloped outline.

2) Canker sores:

The ulcerated region of an aphthous ulcer is surrounded by a smooth, rounded and regular, border.

D) Accompanying symptoms outside the mouth.

1) Oral herpes:

With herpes, a person may experience malaise (a vague feeling of discomfort), fever, joint pain or swollen lymph nodes in the neck.

2) Canker sores:

None of the above symptoms are typical.

Evaluating mouth ulcers that are slow to heal.

When evaluating and monitoring a mouth ulcer, it's important to keep its expected healing time frame in mind.

Canker sores can be expected to heal within a 2-week time period. Ulcers that don't should be viewed with increased suspicion and be evaluated further.

Points keep in mind when evaluating persistent canker sores.

  • They may be long-lasting with people who are immunocompromised (including HIV).
  • Frequent or severe outbreaks can be a symptom of an underlying, undiagnosed medical condition.
  • A persistent lesion may need a biopsy evaluation so it can be differentiated from other types (including squamous cell carcinoma).
  • Any associated sources of mechanical irritation should be removed (sharp teeth or denture edge), otherwise healing may be prolonged.

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