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Causes of a Cold Sore Flareup

Cold sores are caused by the herpes simplex virus (HSV-1). It is contagious and passed from one person to another by infected saliva or direct contact with an active cold sore. After a cold sore heals, HSV-1 remains dormant without symptoms within clusters of cells at the ends of nerves in the face. These clusters are called ganglia, and the virus is able to travel back down a nerve from a ganglion when reactivated through exposure to certain triggers. A cold sore can flare up without warning, but there are circumstances that encourage the infection to recur.

  1. The Cold or Flu Virus

    • When the body's immune system is not working efficiently, cold sores can come back.

      The common cold and flu viruses lower the body's immune system, making it more vulnerable to infection from other sources. In a healthy body, antibodies keep the herpes simplex virus in a dormant state, but if another infection is present the body may not be able to produce enough antibodies to keep both conditions under control, and a cold sore will be able to flare up.

    Too Much Sun

    • An increase in exposure to UV rays can enable HSV-1 to become active again.

      Overexposure to ultraviolet radiation from the sun can trigger the herpes simplex virus. The UV rays stimulate the dormant HSV-1 into an active state, encouraging it to travel back down a nerve from the infected ganglion to the outer skin layer, producing a cold sore blister.

    Stress and Worry

    • Stress increases the chances of cold sore flareups.

      Prolonged periods of worry and stress depress the immune system, making you vulnerable to infection. Stress produces physical symptoms, such as lowered immunity and changes in hormone levels, and these physical changes are triggers for a cold sore flareup, as the herpes simplex virus has a chance to reactivate when the body's natural defenses are low.

    Abrasions or Skin Trauma

    • An open wound can lead to reinfection.

      Abrasions, acne or spots around the mouth leave the skin open to infection or reinfection from the dormant herpes simplex virus. Skin trauma in the same area that a cold sore typically develops enables the infection to flare up, resulting in a newly active and infectious cold sore.

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