Also called cold sores, fever blisters are caused by herpes simplex virus, which makes them highly contagious. The blisters usually affect the gums, the lips or other parts in the mouth.
The herpes simplex virus is usually spread through close contact with an infected person. Practicing hygiene can help in preventing the condition. Fever blisters can be triggered by dental treatment, menstrual periods, stress, infections and exposure to cold or sun. Before the appearance of the sores, a person may experience burning, itching, tingling and pain at the outbreak area. Fever blisters usually heal on their own after a while, as stated by the University of Texas at Austin.