First, it has to be established if the lesion is a cold sore or a canker sore. This can be easily done by your dentist. Cold sores (or fever blisters) usually form in groups as tiny lesions around the mouth or lips and sometimes under the nose. Cold sores are associated with the herpes simplex virus and are very contagious. Once a person is infected with the virus associated with cold sores the person will always keep the virus in their system. Recurrent attacks usually happen when a person is exposed to a fever, sunburn or an increase in stress.
Cold sores last about a week and can be temporarily relieved by some over-the-counter anesthetics and by anti-viral drugs that have been recently released by various pharmaceutical companies. Canker sores (or aphthous ulcer) are small ulcers appearing as a single sore within the mouth. Canker sores are caused by an immune response and are not contagious. Fatigue, stress or even allergies can increase the likelihood that a canker sore may occur. Hot foods and drinks can also contribute to canker sores.
Canker sores also last about a week. People suffering from canker sores should avoid hot, spicy foods and use over-the-counter remedies to decrease the irritation. Sometimes antibiotics also can be used. Remember, the major difference between cold sores and canker sores is whether the sore is located outside or inside the oral cavity.