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What Causes a Cold Sore?

Cold sores are caused by a viral infection involving the herpes simplex virus (HSV). The virus spreads through contact with an infected person, and it can be transmitted even when no cold sores are present. Cold sores usually go away on their own, but there’s no cure for the virus that causes them.

Herpes Simplex Virus

The two types of HSV include:

  • HSV-1, which causes cold sores
  • HSV-2, which causes genital herpes

In some cases, HSV-2 can also lead to the development of cold sores. However, most cold sores are caused by HSV-1.

How HSV-1 Spreads

HSV-1 is a virus that spreads through contact with a person who already has herpes. Usually, this occurs through behaviors such as kissing, sharing utensils, and other skin-to-skin contact. Oral sex can spread HSV-1 to the genitals and HSV-2 to the mouth.

The virus can spread even when someone doesn’t have any active cold sores. However, the virus is most contagious when open sores or blisters are present.

Approximately half of all Americans under 50 are infected with HSV-1.

When Cold Sores Develop

Many people who are infected with HSV-1 never show any signs. If cold sores do develop, they usually go away within about two weeks.

Between outbreaks, the virus continues to lie dormant in the body and can be triggered by a variety of things, including:

  • Viral infections
  • Fevers
  • Fatigue
  • Stress
  • Hormonal changes
  • Immune system changes
  • Exposure to sunlight and wind

Cold Sores Treatment

There is no cure for HSV, but if you get frequent outbreaks you can take prescription antiviral medications to prevent outbreaks or help them heal faster. You can also apply ointments designed to help reduce the pain associated with cold sores.

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