The Mayo clinic states that cold sores are caused by the herpes simplex virus. This virus spreads through skin-to-skin contact, such as kissing and oral sex, as well as by sharing razors, eating utensils or towels. Once an individual has had one outbreak, the virus lies dormant in the nerve cells of the skin of the mouth, making future outbreaks likely.
There is no cure for the herpes simplex virus, but those affected can take preventative measures to reduce the number of outbreaks, according to WebMD. Apply a sun-protective lip-balm to reduce outbreaks due to sun exposure, and avoid foods that are suspected to trigger cold sores, such as gelatin, chocolate and nuts. Wash hands frequently, and don't kiss individuals with active cold sores. Avoid sharing objects that come into contact with another person's lips, such as lipstick or toothbrushes.
Complications from the herpes simplex virus are rare but potentially dangerous. Mayo Clinic warns that individuals with eczema can develop cold sores throughout their bodies, requiring immediate medical care. When introduced into the eye, the virus can lead to conjunctivitis and ulcerations that cause vision loss or blindness. In individuals with compromised immune systems, the virus can also attack the brains, lungs and liver.