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Cold sores are painful red blisters that occur on or around the mouth. They are caused by herpes simplex virus (HSV) types 1 and 2. HSV type 1 is the most common cause of cold sores. HSV type 2 usually causes genital herpes, but it can also cause cold sores. Cold sores tend to appear in the same place every time because the virus lives in the nerves that lead to that spot on the skin.
At least half of all adults are infected with HSdV, which is easily spread from person to person. Once you are infected with HSV, you have the infection permanently. The virus lies "sleeping" inside the nerves, causing no symptoms most of the time. In some people, the virus periodically "wakes up" and causes cold sores.
Conditions that can trigger cold sores include
- hormonal changes
- physical exhaustion.
Cold sores can also often develop with a fever, which is why they are sometimes called "fever blisters."
Symptoms of cold sores
A cold sore usually begins with a slight tenderness or tingling on the edge of the mouth. It develops into a painful, swollen, red lump. After a day or two, the area blisters, bursts, and crusts over. The yellow crust peels away and secretes a clear liquid. It can take up to two weeks for the sore to heal.
Treating cold sores
Applying an over-the-counter antiviral ointment like docosanol (Abreva) at the first sign of a cold sore can help shorten its duration. But doing this will not prevent cold sores from appearing again. Stronger prescription antiviral ointments include acyclovir (Zovirax) and penciclovir (Denavir).
Over-the-counter anesthetics can numb the skin and help relieve pain and discomfort. These include benzocaine (Orajel), lidocaine (Zilactin-L), and tetracaine (Viractin). Applying ice at the first sign of tenderness or tingling may help shorten the duration of the sore, or prevent it from becoming a full-blown cold sore.
Taking a prescription antiviral medicine may be an option for people who have frequent, painful cold sores.
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.
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