Cold sores, also known as fever blisters, are tiny, clear, fluid-filled blisters that form around the mouth and are caused by the herpes simplex virus (usually type 1, or HSV-1) living inside your nerve tissue. Cold sores usually do not last longer than two weeks. However, the sores are highly contagious and tend to recur when the virus is reactivated by a trigger such as stress, sunlight, fever or illness.

Like cold sores, canker sores ? also known as aphthous ulcers ? can be quite painful and often recur. While cold sores are caused by a virus, the formation of a canker sore may be triggered by multiple factors such as stress, food allergies or a weakened immune system. A canker sore forms in the soft tissues of your mouth and is not contagious, whereas a cold sore usually appears around the lip area outside the mouth and is highly contagious. If a cold sore appears inside the mouth, usually it appears on the non-movable parts such as the roof, rather than the tongue or soft palate.

Most people get HSV-1 infections during infancy or childhood and usually catch the virus from an infected family member or friend. Only an estimated 30 percent of those infected actually develop the characteristic blisters. If sores do develop, they can appear anywhere from two to 12 days after exposure to an infected person. Other persons with a primary infection may have flu-like symptoms such as a high fever, sore throat, swollen neck glands and mouth soreness.

Day 1: Prodrome (tingle) stage - Before a cold sore has formed, you may feel a tingling, itching or burning sensation beneath the skin, usually around the mouth or the base of the nose. Applying antiviral medications during this stage can help alleviate cold-sore symptoms.

Days 2 to 3: Blister stage - An outbreak of fluid-filled blisters is the first visible sign of cold-sore formation.

Day 4: Ulcer or weeping stage - Typically, the most contagious and painful stage of cold sores is when blisters rupture, leaving a shallow, reddish, open sore.

Days 5 to 8: Crusting stage - After a few days, the blisters dry up and form a yellow or brownish crust, which eventually falls off. During this stage, it is important to care for the scab, which can crack or break.

Days 9 to 12: Healing stage - Usually a series of scabs will form on the lesion, which eventually flake off. Each new scab will be smaller than the previous one, until the cold sore heals completely, usually without scarring.

There may be long periods when the herpes virus remains inactive. The following factors can trigger cold sores:

•  Illness, such as cold or flu
•  Dental treatment
•  Physical stress or fatigue
•  Menstruation or pregnancy
•  Mouth trauma
•  An immune-system deficiency
•  Sunlight exposure or ultraviolet lamps
•  Food allergies

Most cold sores are mild and do not require treatment. Antiviral medications can reduce the frequency, duration and severity of outbreaks. Medications with a numbing agent, such as benzyl alcohol, can help alleviate a cold sore's burning, itching and pain. Emollients can reduce cracking and soften scabs. Applying aloe vera balm three times a day to the cold sore also can help fight the infection and enhance healing.

If over-the-counter remedies don't help, ask your dentist for a prescription. A dentist also can accurately diagnose cold sores and base treatment on important factors such as your age, overall health, medical history and tolerance for specific medications.

To prevent transmission of the virus to another person, avoid:

•  Intimate physical contact with others
•  Sharing eating utensils, toothbrushes, towels and razors
•  Touching the blisters (always wash your hands after applying medication)

How to minimize recurrent outbreaks:

•  Eat foods high in lysine (an amino acid found in red meats, fish and dairy products) or take supplements
•  Apply sunscreen to the face and lips before going outdoors
   Shave with a disposable razor during an outbreak
•  Replace your toothbrush
•  Engage in relaxing activities to reduce stress