Patient Resources

Fever Blisters and Canker Sores

If you have been bothered by a sore in your mouth that made it painful to eat and talk, you are not alone. Many others suffer from recurrent mouth sores. Two of the most common recurrent oral lesions are fever blisters (cold sores) and canker sores (aphthous ulcers). When they occur in the mouth, it may be difficult to distinguish one from the other. Since the treatment and cause of these two sores are completely different, it is extremely important to know which is which.

What are fever blisters (cold sores)?

These are common names for fluid filled blisters that commonly occur on the lips. They also can occur in the mouth, particularly on the gums and roof of the mouth (hard palate), but this is rare. Fever blisters are usually painful and the pain may precede the appearance of the blister by a few days. The blisters rupture within hours and then crust over, lasting approximately 7-10 days.

Causes
Fever blisters result from a herpes simplex virus which becomes active. This virus is latent (dormant) in afflicted people, but can be activated by conditions such as stress, fever, trauma, hormonal changes and exposure to sunlight. When blisters reappear, they tend to form in the same location.

Can fever blisters be spread?
Yes. The time from blister rupture until the sore is completely healed is the time of greatest risk for spread of infection. The virus can spread to your own eyes and genitalia, as well as to other people.

Treatment
Treatment consists of coating the lesions ointment containing an antiviral agent, for example 5% acyclovir ointment. Presently, there is no cure, but there is much research activity underway in this field. Contact your doctor or dentist for the latest information.

Prevention Tips:
Avoid mucous membrane contact when a lesion is present. Do not squeeze, pinch or pick at the blister. Wash hands carefully before touching your eyes or genital area, or another person. Despite all caution, it is important to remember that it is possible to transmit herpes virus even when no blisters are present.

What are canker sores?

Canker sores (aphthous ulcers) are small, shallow ulcers occurring on the tongue, soft palate or inside the lips and cheeks. They are quite painful and usually last 5-10 days.

Causes

The best available evidence suggests that canker sores result from an altered local immune response associated with stress, trauma or local irritants such as eating acidic foods (tomatoes, citrus fruits and some nuts).

Can canker sores be spread?

No. Since they are not caused by bacteria or viral agents, they cannot be spread locally or to anyone else.

Treatment

The treatment works to relieve discomfort and guard against infection. A topical corticosteroid preparation such as triamcinolone dental paste (Kenalog in Orabase O.1%®) is helpful. Unfortunately, no cure exists at present.