Painful lesions that develop in or around the mouth are often mistaken for one another, but cold sores and canker sores are two distinct conditions with separate origins and management approaches. Cold sores, also known as fever blisters, are an external manifestation of a viral infection, while canker sores are ulcers that form internally. Understanding the fundamental differences in what causes them, where they appear, and how they are treated provides a clearer path to relief.
Cause and Contagion
A cold sore is caused by the herpes simplex virus type 1 (HSV-1), a highly contagious pathogen that is transmitted through close contact, such as kissing or sharing eating utensils during an active outbreak. Once a person is infected, the HSV-1 virus does not leave the body but instead retreats to the nerve cells, remaining dormant until certain triggers cause it to reactivate. Common triggers for reactivation include stress, sun exposure, hormonal changes, or a temporary weakening of the immune system.
Canker sores, medically termed aphthous ulcers, are fundamentally different because they are not caused by a virus and are not contagious. The exact cause of these ulcers is not fully known, but they are believed to be related to an immune response. Factors that can trigger their formation include minor trauma to the mouth lining, such as accidentally biting the cheek, or sensitivities to certain acidic foods. Nutritional deficiencies, particularly in vitamin B12, folic acid, or iron, and high levels of emotional stress are also commonly associated with outbreaks.
Location and Appearance
Cold sores almost always appear on the outside of the mouth, most frequently forming on the border of the lips, known as the vermilion border. They begin as a localized tingling or burning sensation before progressing into small, painful, fluid-filled blisters that often appear in clusters. These blisters eventually rupture, ooze, and then crust over, forming a scab as they heal.
Canker sores are found exclusively inside the mouth on soft, movable tissues. They appear on the inner cheeks, the tongue, the soft palate, or the inner surface of the lips. These lesions present as a single, distinct ulcer that is round or oval in shape. They possess a clear physical hallmark: a center that is white, gray, or yellowish, surrounded by a sharply defined, inflamed red border.
Treatment and Management
Cold sore management focuses on reducing the viral load and accelerating the healing process. Topical or oral antiviral medications, such as acyclovir or penciclovir, can be prescribed to shorten the duration of an outbreak, especially if applied at the first sign of tingling. Given the contagious nature of the herpes simplex virus, patients are advised to avoid close personal contact and sharing items like towels or drinking glasses until the sore is fully crusted and healed.
The treatment for canker sores is aimed at relieving pain and managing the inflammation. Over-the-counter topical anesthetics and protective occlusive agents can be applied directly to the ulcer to shield the exposed nerve endings. Rinsing the mouth with a warm salt water solution or a medicated rinse can also help soothe the area and promote healing. If the sores are unusually large, highly frequent, or persist for more than two weeks, professional medical advice should be sought to rule out underlying issues.