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.

Canker vs.

Link to Location Comparison graphic.

Canker vs.

Link to pictures of herpes and canker sores.

Differentiating between herpetic and aphthous oral lesions.

Of all of the different kinds of mouth ulcers that are commonly mistaken for canker sores (formally referred to as recurrent minor aphthous ulcers), the type that's most frequently confused is the recurring intraoral herpes lesion. This page explains how to tell these two apart.

Note: The term "intraoral" used here indicates that the herpes sores in question form inside the mouth, as opposed to those types of herpetic lesions (like cold sores) that form outside of it (like on the lips or nearby facial skin). Learn more about distinguishing cold sores.

Are canker sores the same as herpes?

No, they are not. Canker sores are not caused by the herpes virus but instead by a person's own immune system's response. For specific details:


How can you tell the two apart?

There are some very distinct differences between herpes and aphthous lesions, and they are very easy to take notice of and identify. 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 keratinized oral tissues. These are the "tougher," firmer type of gum tissue found in the mouth.

Keratinized tissues are sometimes described as being bone-bearing, meaning that they're tightly bound as a covering over the bony structures that lie underneath them.

Keratinized oral tissues include: (See Frame 1 of our animated graphic.)

a) The skin covering the hard palate. - This is the most likely location for intraoral herpetic lesions to form.

b) Attached gingiva. - This term refers to the gum tissue that surrounds the teeth and covers over the portion of the jawbone that encases them.

Canker sores vs. Oral Herpes.

Slideshow 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 the mouth's non-keratinized tissues. These are the softer, more fragile type of skin surfaces.
When you touch them, they move around freely. And for this reason, dentists commonly refer to them as "loose" tissue.
Non-keratinized oral tissues include: (See Frame 2 of our animated graphic.)
  • a) The inside lining of the cheeks or lips.
  • b) The underside of the tongue.
  • c) The floor of the mouth.
  • d) In the back of the mouth, near the tonsils.
  • e) The soft palate.
(Locations listed in order of likelihood of canker sore formation.)

Section references - Neville, Scully, Mortazavi, Dunlap

Takeaways from this section.

You should be able to base most of your differentiation process just on the location of the sore alone.

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 of an inch (1mm) across.
  • In our animated graphic 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 reddened area (a macule) on the surface of the mouth's lining that has an associated tingling, burning or itching sensation.
  • It then transforms into an ulceration that may become as large as 1/4 of an inch.


Takeaways from this section.

Blister formation is a primary key in differentiating between aphthous and herpetic lesions.

  • 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 herpetic blisters form they tend to burst fairly quickly, possibly before you've had a chance to actually notice them.


Oral Herpes vs. Canker sores.

Slideshow showing pictures of the differences 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 animated graphic.)

Compare: Canker sores

With aphthous lesions, the outline of the ulcerated area is usually round or ovoid, and surrounded by a smooth, regular (not jagged) red border. (See Frame 2 of our animated graphic.)

Takeaways from this section.

The general rule of thumb when distinguishing between the two is:

  • 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.


Takeaways from this section.

Location, location, location:

  • If it's always generally the same = herpes.
  • If it's variable = canker.


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 you don't really notice them.

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 just 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, with dental work frequently being the cause. As examples:

  • 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 (see links above) specifically cite 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 suggests 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 See the list.. Or, the lesion may be a different form of aphthous ulcer (major aphthae How they differ.).


Takeaways from this section.

If the course of the ulceration you've been monitoring begins to stray from the expected norm, it requires 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.

Section references - Primary reference sources for this entire page: Neville, Scully, Mortazavi, Dunlap


 Page references sources: 

Dunlap CL, et al. A guide to common oral lesions.

Mortazavi H, et al. Diagnostic Features of Common Oral Ulcerative Lesions: An Updated Decision Tree.

Neville BW, et al. Oral and Maxillofacial Pathology. Chapter: Allergies and Immunologic Diseases.

Scully C, et al. Oral medicine — Update for the dental practitioner Aphthous and other common ulcers.

All reference sources for topic Canker Sores.