Oral herpes vs. Canker sores.

- What's the difference between them, or are they the same thing? / How to tell them apart by appearance, location and symptoms.

Page Graphics | Animations.
Link to Location Comparison graphic.
Link to pictures of herpes and canker sores.

Of all of the different types of mouth ulcers that are frequently mistaken for canker sores (aphthous ulcers), the most common one is the recurring intraoral herpes lesion. (The term "intraoral" means that the sore forms inside the mouth, as opposed to herpetic lesions like cold sores that form on the skin around it.)

Are canker sores herpes?

No, they are not a type of herpetic lesion. (For details, here's information about why they form and what triggers outbreaks. In comparison, here's information about the herpes virus and the types of lesions it can cause.)

How do you tell the two apart?

As outlined on the remainder of this page, there are some very distinct differences between these two types of mouth lesions and they are easy to pick out.


A) Canker sores and oral herpes form in different locations.

1) Intraoral herpetic lesions.

Herpes lesions form on firmly attached, keratinized oral tissues. (These types of skin are sometimes referred to as bone-bearing, meaning that they're tightly bound to the bone structure that lies underneath them.)

These tissues include (See Frame 1 of our animation):

a) The skin covering the hard palate. (This is the most likely location for these lesions to form.)

b) The attached gingiva (the gum tissue that surrounds the teeth and surrounding bone tissue).

Diagram showing where aphthous ulcers and oral herpes usually form.

Oral herpes (Slide 1) and canker sores (Slide 2) form in different locations.

2) Canker sores.

In comparison, aphthous ulcers form on loose, non-keratinized tissues of the mouth. (These are skin surfaces that when you touch them they move around freely.)

These include (See Frame 2 of our animation):

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) The early stages of canker and herpes sores look different.

1) Intraoral herpetic lesions.

These sores first appear as a group of tiny vesicles (blisters). Each one is usually no more than about 1/25 th of an inch (1mm) across. (In our animation below, you can actually see a vesicle in the lower right corner that hasn't yet burst.)

2) Canker sores.

These lesions first appear as a raised, reddened area that may have a tingling sensation. It then transforms into an ulceration that may become as large as 1/4 of an inch.

Pictures showing the difference between oral herpes and aphthous ulcers.

The shape of intraoral herpes (Slide 1) is entirely different than a canker sore (Slide 2).

C) The shape of the ulcerations is different.

1) Intraoral herpes.

The individual areas where a blister has ruptured coalesce (join together) to form a larger sore. This gives the outline of the combined ulceration a scalloped (lobed) shape. (See Frame 1 of our graphic.)

2) Canker sores:

The ulcerated area is surrounded by a smooth, rounded and regular, red border. (See Frame 2 of our graphic.)

D) Distribution in the mouth.

In the case where you've experienced the same type of mouth sore before, the location where your current one has formed can help you distinguish between the two.

Oral herpes lesions tend to recur in the same general area as they have before. In comparison, aphthous ulcers don't usually show this same correlation and often appear in entirely different areas each time.

E) Accompanying symptoms outside the mouth.

1) Intraoral herpes.

With herpes, a person may experience malaise (bodily weakness or discomfort), fever, joint pain or swollen lymph nodes in the neck. Although, these symptoms may be slight enough that they're not readily noticed.

2) Canker sores.

None of the above symptoms are typical. In fact, the most common set of events is one where a lesion has formed but otherwise you feel completely normal.

F) Other tip-offs.

A canker sore may be, in some cases, preceded by some type of tissue trauma. In comparison, recurrent intraoral herpes lesions typically are triggered by it.

This trauma is often the result of dental work, such as getting an injection (a "shot") or having a periodontal (gum) procedure performed in the area.

G) Healing time frames.

Both types of ulcerations can be expected to heal on their own within a 1 to 2 week time period.

Persistent sores require evaluation.

Mouth sores that persist for longer than two weeks may still be canker or intraoral herpes lesions. But this delay suggest that complicating factors are involved and closer evaluation is needed so appropriate treatment can be started.

  • The delay might be due to some persistent source of mechanical irritation (like a broken tooth or sharp denture edge).
  • Biopsy evaluation may be needed so the lesion can be differentiated from other types of mouth sores (including squamous cell carcinoma).
  • With herpes, people having a compromised immune system (such as that due to HIV/AIDS, leukemia or taking organ-transplant medications) may experience persistent ulcerations (that may even spread). In these cases, the use of antiviral drugs is likely indicated.
  • Persistent canker ulcerations, or frequent or severe outbreaks, can be a symptom of an undiagnosed underlying medical condition. Or, the lesion may be a different form of aphthous ulcer (major aphthae).



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