Sores or blisters on the lips or mouth or in the throat are usually caused by one of two conditions. One is an infection by the virus herpes simplex; the other is a condition called aphthous ulcers, whose cause is unknown.
Herpes simplex-The sores in the mouth called cold sores or fever blisters can be an infection caused by the herpes simplex virus. The sores usually start as an area of irritation or pain that becomes inflamed, then forms a watery blister that breaks and forms an open sore with pus, and finally scabs over and heals. The sores occur on the lips, in the mouth along the cheeks, on the roof of the mouth or palate, or on the back of the mouth. These sores are usually round or oval, measure about a quarter of an inch or less in diameter, and can have a characteristic white raised border. The sores of herpes can be very painful and often interfere with chewing; when in the back of the mouth or esophagus, the sores can interfere with swallowing.
Herpes simplex remains in the nerves serving the area of the mouth for the remainder of the person’s life; it can be reactivated and cause new sores. The interval between outbreaks is unpredictable, but outbreaks are frequently associated with stress, exposure to sunlight, surgery, colds, menstrual periods, fever, and pneumonia. These associations explain the common name of these sores: cold sores or fever blisters.
Infections of the mouth from herpes simplex are extremely common: probably 50 percent of healthy Americans have had this infection at some time. Herpes simplex infections of the mouth are more frequent, more severe, and last for longer periods in people with HIV infection. This is especially true of the later stages of the disease when the CD4 cell count is low and other types of infections are also more common.
Herpes simplex can be spread to others, but many people already have had it, and others who get it develop only trivial problems. When sores are active, it is reasonable to exercise restraint in contact such as kissing and to avoid sharing items that might have saliva on them.
The usual treatment is with acyclovir (Zovirax). Acyclovir is available as an ointment to place on top of sores, as a pill to take by mouth, or as an intravenous preparation. Administration by mouth or by vein is usually preferred, though the choice between options depends largely on the severity of the sores. Because herpes simplex infections tend to recur when treatment is discontinued, long-term treatment with acyclovir by mouth is sometimes advocated once the sores have healed.