Cold sores are caused by the herpes simplex virus. Type 1 of this virus typically causes cold sores on the lips and facial areas. They are very contagious, and can spread from kissing. Most Americans have the Type 1 virus by age 20, notes the Florida Health Finder. About 45 to 80 percent of kids and grownups in America have had an outbreak of cold sores, notes the National Institute of Dental and Craniofacial Research.
Stress
One reason for a cold sore to appear is emotional stress, notes WomensHealth.gov. Any high stress time period can activate the virus lingering in the cheekbone area of the body causing an outbreak of cold sores to appear.
Illness & Fever
An illness provides another reason for a cold sore to appear, notes Florida Health Finder. When the immune system becomes weakened due to illness, the herpes virus can activate and cause cold sores. Spiking a fever also often activates the herpes virus, notes the National Institute of Dental and Craniofacial Research.
Sunlight
Exposure to sunlight presents an additional reason for cold sores to pop up. The sun stimulates the virus to become active again and create a cold sore. Placing sunscreen on the lips can help to prevent cold sores, notes the National Institute of Dental and Craniofacial Research.
Infected Items
A cold sore may also appear due to contact with an item infected with the herpes simplex virus. Items such as razors, bath towels and dishes can harbor the virus and transmit it to anyone who touches the object, notes Florida Health Finder.
Menstrual Period
The menstrual period is another reason why a cold sore can arise, notes Florida Health Finder. The hormonal changes in the body as the menstrual cycle begins may trigger activation of the herpes virus.
Oral Sex
Cold sores sometimes also appear due to direct oral contact with the genitals of someone with herpes, notes Florida Health Finder. Oral sex can cause both type 1 and type 2 herpes virus cold sores to appear.
Unknown Causes
Scientists also suspect that numerous other unknown causes that activate the appearance of cold sores exist. Research is ongoing to identify all causes of this common disorder.
