Most mouth sores are cold sores (also called fever blisters), canker sores, or other irritation caused by:

• Biting your cheek, tongue, or lip
• Chewing tobacco
• Braces
• A sharp or broken tooth or poorly fitting dentures
• Burning your mouth from hot food or drinks

Cold sores are caused by herpes simplex virus and are very contagious. Usually, you have tenderness, tingling, or burning before the actual sore appears. Herpes sores begin as blisters and then crust over.

The herpes virus can reside in your body for years, appearing as a mouth sore only when something provokes it. Such circumstances may include another illness, especially if there is a fever, stress, hormonal changes (such as menstruation), and sun exposure.

Canker sores are NOT contagious and can appear as a single pale or yellow ulcer with a red outer ring, or as a cluster of such lesions. The cause of canker sores is not entirely clear, but may be related to:

• A virus
• A temporary weakness in your immune system (for example, from cold or flu)
• Hormonal changes
• Mechanical irritation
• Stress
• Low levels of vitamin B12 or folate

For unknown reasons, women seem to get canker sores more often than men. This may be related to hormonal changes.

Less commonly, mouth sores can be a sign of an underlying illness, tumor, or reaction to a medication. Such potential illnesses can be grouped into several broad categories:

• Infection (such as hand-foot-mouth syndrome)
• Autoimmune diseases (including lupus)
• Bleeding disorders
• Malignancy (cancer)
• Immunosuppression (that is, when your immune system is weakened -- for example, if you have AIDS or are receiving medication after a transplant).

Drugs that might cause mouth sores include chemotherapeutic agents for cancer, aspirin, barbiturates (used for insomnia), gold (used for rheumatoid arthritis), penicillin, phenytoin (used for seizures), streptomycin, or sulfonamides.

Mouth sores generally last 10 to 14 days, even if you don't do anything. They sometimes last up to 6 weeks. The following steps can make you feel better:

• Gargle with cool water or eat popsicles. This is particularly helpful if you have a mouth burn.
• Avoid hot beverages and foods, spicy and salty foods, and citrus.
• Take pain relievers like acetaminophen.

For canker sores:

• Rinse with salt water.
• Apply a thin paste of baking soda and water.
• Mix 1 part hydrogen peroxide with 1 part water and apply this mixture to the lesions using a cotton swab.

Nonprescription preparations, like Orabase, can protect a sore inside the lip and on the gums. Blistex or Campho-Phenique may provide some relief of canker sores and fever blisters, especially if applied when the sore initially appears.

Additional steps that may help cold sores or fever blisters:

• Apply ice to the lesion.
• Take L-lysine tablets.

Anti-viral medications for herpes lesions of the mouth may be recommended by your doctor. Some experts feel that they shorten the time that the blisters are present, while others claim that these drugs make no difference.