Various types of mouth sores can appear in or around the mouth for a number of reasons. Injuries to the mouth, such as a bite to the inside of the cheek, are common sources. Chemical or allergic irritation can cause blisters and ulcers to form, and cold sores or fever blisters will form as the result of a viral infection. The causes of one type, called canker sores, are not fully understood, but they are believed to be related to the immune system. Many other conditions can trigger sores in the mouth as well, but these are some of the most common.
Injury is perhaps the simplest cause for mouth sores; a cut or scrape to the inside of the mouth causes injury in the form of an ulcer or blister. Blistered, fluid-filled sores in the mouth are referred to as vesicles or bullae, depending on the sore’s size. Chemical burns and allergic reactions to food or medications also can create sores. They often are quite painful, especially when eating salty or acidic foods, until they've had a chance to heal.
Viral infection is a common cause of mouth sores. The familiar cold sores and fever blisters are caused by herpes simplex virus (HSV) type I and are highly contagious, often passed on through contact with infected skin or saliva. HSV infections are perhaps the best known source, but other viral, fungal and bacterial infections, such as syphilis and herpes zoster, the virus that causes chicken pox and shingles, also can trigger blisters and ulcers in and around the mouth. Bacterial infections of the teeth or gums can cause an abscess or cellulitis and are potentially serious.
Canker sores, also known as aphthous stomatitis, are another very common type of sore in the mouth. These recurring sores are not contagious and seem to be triggered by an immune system reaction, although the actual cause is unknown. Canker sores form as oval ulcers with a white center. They are painful, but usually disappear within two weeks without complication. Larger sores, however, can take longer to heal and can cause scarring.
Treatment for mouth sores varies depending on the cause, but many require only time to heal. An anesthetic mouthwash or lozenge might help reduce the pain. The entire mouth should also be cleaned frequently with a soft toothbrush to help prevent infection. Treatment with medicated gels, chemicals, or laser treatments might also be recommended by a medical professional.