Cold sores are caused by certain strains of the herpes simplex virus (HSV). HSV-1 usually causes cold sores. HSV-2 is usually responsible for genital herpes. However, either type can cause sores in the facial area or on the genitals. Most people who are infected with the virus that causes cold sores never develop signs and symptoms.

Cold sores are most contagious when oozing blisters are present. But you can transmit the virus to others even if you don't have blisters. Shared eating utensils, razors and towels, as well as kissing, may spread HSV-1. Oral sex can spread HSV-1 to the genitals and HSV-2 to the lips.

Once you've had an episode of herpes infection, the virus lies dormant in nerve cells in your skin and may emerge as another cold sore at the same place as before. Recurrence may be triggered by:

  • Viral infection or fever
  • Hormonal changes, such as those related to menstruation
  • Stress
  • Fatigue
  • Exposure to sunlight and wind
  • Changes in the immune system
May 15, 2015