The virus is transmitted by direct contact with fluids from an infected person, as might occur when sharing utensils. Although it can cause flu-like symptoms, the initial infection is often undetected. Afterward, the virus becomes dormant and resides in the nerves that serve the mouth and oral cavity, until a trigger initiates active infection. Any factor that suppresses the immune system can act as a trigger. Among the most common are ultraviolet light, stress, lack of sleep, and certain medications.
Food allergies can also trigger flare-ups.
Limiting exposure to triggers can help prevent episodes. Sun protection, adequate sleep, a healthy diet, exercise, and stress reduction are all beneficial. Avoid using greasy lip ointments, such as petroleum jelly, on an active cold sore. Such ointments can spread viral particles to neighboring areas of the face, leading to new sores. In severe cases, nausea and vomiting may occur, standing may be impossible, and hearing loss may become permanent.