Skip to main content

Cold Sore Causes

Cold Sore Common Causes

The most common cause of cold sores is coming in contact with the herpes simplex 1 virus. This highly contagious virus can be contracted by coming in contact with another person who has a cold sore through touching and kissing, or from sharing lipstick, lip balm, a razor, towel, toothbrush, silverware, or a cup.

The virus usually enters the body through a break in the skin or through the mouth. The cold sore virus is usually inactive until a trigger activates it and causes a cold sore outbreak.

Common triggers include:

  • Sunlight exposure on the face and lips
  • Fatigue
  • Stress
  • Cold weather
  • Hormone changes
  • Cold or flu
  • Allergies to food or medicine
  • Dental treatment that causes an injury to the lips or gums
  • A weak or impaired immune system
  • Cosmetic surgery such as laser skin resurfacing or dermal abrasion

Becoming deeply sad or upset and getting injured in the facial region can also trigger a cold sore. If you have a weak immune system during an outbreak, it may take longer than usual for the cold sore to heal and the symptoms may be more severe. Cold sores are more prone in people who have weak immune systems including infants and people with cancer or HIV/AIDS.

Although herpes simplex 1 virus is the cause of most cold sores, genital herpes from the herpes simplex 2 virus may also develop on the lips if you have oral sex with someone who has the virus.