Aphthous Ulcers vs. Cold Sores

Mouth ulcers are a common concern for patients. The phrase “mouth ulcer” is a general name or description of any sore or ulceration in the mouth. The most common type of mouth ulcer is an aphthous ulcer, also known as a canker sore. Canker sores differ from cold sores, but many of our patients question the difference. Both can be painful, but they have separate causes and presentations. The easiest way to know if you have a cold sore or a canker sore is by noting what it looks like and where it occurs. See below for a detailed explanation of aphthous ulcers (canker sores) vs. a herpetic outbreak (cold sores). 

What is a Canker Sore?

Aphthous ulcers occur inside the mouth and are generally white or yellow sores with a red border. These small, round ulcers may form on your gums, tongue, inner lips or cheeks, or palate (roof of mouth). They are generally harmless but can cause discomfort during everyday activities such as eating or speaking. 

Person holding lower lip to show aphthous ulcer on inside of lip.
Aphthous Ulcer (Canker Sore) on the Inner Lip


Canker sores do not have one specific cause. They can form after minor tissue trauma from dental procedures or accidental biting of your inner cheek or tongue. Citrus, nuts, chocolate, or other foods can also lead to mouth ulcers. Other triggers of aphthous ulcers include smoking, vitamin deficiencies, particular types of toothpaste containing Sodium Lauryl Sulfate (SLS), and stress. 


Aphthous ulcers are not contagious and can heal on their own over time. Drinking plenty of water, practicing good oral hygiene, and avoiding acidic, abrasive, or spicy foods can help the healing process. Your dental provider may recommend medications such as a steroid ointment like triamcinolone to ease discomfort caused by canker sores. Patients can also use over-the-counter medications such as Orajel. 

What is a Cold Sore?

 A cold sore occurs on the outside of the mouth near the lips. It typically appears as a patch of small fluid-filled blisters, which is why cold sores are also called fever blisters. Other symptoms can include a burning or tingling sensation at the blister site and sometimes fever or swelling of the lymph nodes. 


According to the National Institute of Dental and Craniofacial Research, “fever blisters are caused by an infection with the herpes simplex virus, usually type 1, or HSV-1”. Active flare-ups of the virus, known as a herpetic outbreak, cause fever blisters. Some people may experience no symptoms after exposure to the virus, while others may have reoccurring fever blisters. More information can be found directly on the National Institute of Health website by following this link

woman's lips with cold sore
Cold Sore


Once a person has the initial infection of the herpes simplex virus, the virus can stay latent on a nerve dermatome. Stress and excess UV sun exposure are often triggers of recurrences. Recurrent episodes usually begin with symptoms of tingling, itching, or burning near where the sores will appear. To minimize pain and aid in recovery, your dental provider can prescribe antiviral medications to halt the reproduction of the virus and stop the blister before it starts. Cold sores are contagious, so do not share eating utensils or cups, and avoid kissing if you have symptoms. Your dental provider will ask you to reschedule appointments if you have active sores to minimize the risk of spreading the virus.


Canker and cold sores are often confused, but each has distinct differences. Aphthous ulcers (canker sores) occur inside the mouth and are not contagious, while herpetic outbreaks (fever blisters/cold sores) occur outside the mouth and are highly infectious. Both can be painful, but there are treatment options to alleviate any discomfort. Contact your dental provider if your symptoms do not improve after trying at-home remedies or if they last more than a few weeks. Please give us a call if you have any other questions!