Canker sores vs. oral herpes.

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

Links to page graphics.
Link to Location Comparison graphic.
Link to pictures of herpes and canker sores.

Of all of the different types of mouth ulcers that are commonly mistaken for canker sores (aphthous ulcers), the most frequent kind is the recurring intraoral herpes lesion. This page explains how to tell these two apart.

Note: The term "intraoral" indicates that the sores in question form inside the mouth, as opposed to those types of herpetic lesions (like cold sores) that form outside the mouth (on the lips or adjacent facial skin).

So, are canker sores herpes?

No, they are not. They are not caused by the herpes virus but instead by an entirely different set of circumstances. For specific details:

How can you tell the two apart?

There are some very distinct differences between herpes and apthous lesions and they are easy to pick out. The remainder of this page explains what to look for.


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

Compare: Intraoral herpes

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

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.

Compare: 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.

Takeaways from this section.

You should be able to base most of your diagnosis just on the location of the sore. There can be exceptions but not usually with the type of common run-of-the-mill lesions you're most likely to encounter.

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

Compare: Intraoral herpes

Herpetic 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.

Compare: 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.
Takeaways from this section.

If you see tiny blisters form, you don't have a canker sore. However, if you don't see them it doesn't absolutely rule out herpes.

That's because after they form they tend to burst fairly quickly, possibly before you've had a chance to actually see them.

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.

Compare: Intraoral herpes

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

Compare: Canker sores

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

Takeaways from this section.

General rule of thumb when distinguishing between the two: Round or ovoid lesions = canker. Irregular shapes = herpes.

D) Distribution in the mouth.

In the case where you've had the same type of mouth sore before, the location where your current one has formed can help you to make a distinction between the two types of lesions.

  • Oral herpes tends to recur in the same general area as before.
  • In comparison, aphthous ulcers don't necessarily show this same correlation. They often appear in entirely different areas each time.

E) Accompanying symptoms outside the mouth.

Compare: 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.

Compare: 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.

Takeaways from this section.

If you've been sick, or even a little under the weather, think herpes outbreak.

F) Other tip-offs.

The formation of a canker sore is sometimes preceded by some type of traumatic act, like biting or scraping the soft lining of your mouth.

In comparison, intraoral herpes lesions are often triggered by some type of traumatic event.

Dental work is frequently the cause, such as:

  • Receiving a dental injection (getting a "shot").
  • Having some type of periodontal (gum) procedure performed in the area of the breakout.
Takeaways from this section.

The majority of reference sources used to create this page specifically cited the above two dental procedures as the classic triggering event for intraoral herpes.

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).
Takeaways from this section.

If the course of the ulceration you've been monitoring begins to stray from the norm, you require an evaluation by your dentist.

The hope is that the problem they discover is easily resolved. For example, possibly a rough tooth or denture flange just needs to be polished down.

But in some instances, they may find a serious situation that without treatment might have led to a severely extended or complicated healing process, or possibly even a life-threatening event.



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