What Causes Blisters to Form Inside of the Mouth?

Fever blisters, otherwise known as cold sores, are caused by the herpes simplex virus that becomes active at various times, according to the American Academy of Otolaryngology — Head and Neck Surgery. Fever blisters are fluid-filled blisters that form on the lips, gums and possibly the roof of the mouth.

Fever blisters are painful and usually precede lesions around the mouth. Cold sores rupture and then crust over before going away completely after seven to 10 days. The herpes simplex virus lays dormant in patients until some conditions such as stress, trauma, fever, exposure to sunlight or hormones activate the disease. Fever blisters tend to appear in the same spots when they reoccur, notes the AAO-HNS. Fever blisters are contagious, especially from the time they rupture until the sore heals completely. The virus can spread to other areas of the body, and to other people, during the contagious time.

Over-the-counter medications can help relieve pain associated with fever blisters, especially if the medicine is used when the cold sores first appear. Patients can also apply ice to the sores to alleviate pain and soreness, according to MedlinePlus. Remedies such as saltwater gargling, oral pain relievers and frozen ice pops can relieve pain. Doctors suggest avoiding hot beverages, hot foods, anything citrus, spicy foods and salty foods when cold sores flare up.