What is a cold sore?

A cold sore is a fluid-filled blister (or a cluster of blisters) that appears on the lips and around the mouth. Cold sores are also called fever blisters, oral herpes or herpes labialis.

While cold sores are highly contagious, they usually aren’t serious. In healthy people, cold sores generally clear up on their own in one to two weeks.

How common are cold sores?

Cold sores are widespread. More than half of the people in the United States have been infected with the virus that causes cold sores, though many people never develop cold sores or have any symptoms. About 20 to 40 percent of people who have the virus develop cold sores.

How often do people get cold sores?

A cold sore can develop multiple times a year or only once or twice in your lifetime. The frequency of a cold sore outbreak varies from person to person.

Who is affected by cold sores?

People of all ages can become infected with the virus that causes cold sores. Many people are exposed to the virus during childhood.

It is possible to develop a cold sore at any age, though the chance of having a cold sore outbreak decreases after the age of 35.

What are the symptoms of cold sores?

For many people, symptoms are more severe the first time they develop a cold sore. When you have a cold sore outbreak:

  • The first sign of a cold sore is usually a tingling, burning, or itching sensation on or around the lips, beginning about 12-24 hours before the cold sore develops.
  • The area becomes red, swollen and painful as the blisters form.
  • Over 2-3 days, the blisters rupture and ooze fluid that is clear or slightly yellow. This is sometimes called the “weeping phase.”
  • About 4-5 days after the cold sore appears, it crusts and scabs over. It might crack or bleed as it heals.
  • The scab then falls off, revealing skin that may be a little more pink or reddish than usual for a few days. It usually takes 1-2 weeks for the cold sore to heal completely.

What causes cold sores?

Cold sores are sometimes called oral herpes because they are caused by the herpes simplex virus type 1 (HSV-1). This virus is very common and highly contagious. It spreads through saliva or close contact — often through kissing or by sharing utensils, straws, towels or lip balm with someone who has a cold sore.

You may not know if you have been infected with HSV-1 because symptoms of exposure to HSV-1 are generally mild. Children sometimes develop a fever and small blisters inside and around their mouths when they are first exposed to HSV-1.

What triggers a cold sore?

After you have been infected with HSV-1, the virus never goes away. It remains dormant (inactive) in a group of nerve cells in your face called the trigeminal ganglion.

When the virus is triggered, or activated, it “wakes up” and travels through your nerves to your lips, where a cold sore develops. After an outbreak, the virus goes back to sleep in your body.

What triggers a cold sore in one person might not cause an outbreak in another person. Some people with HSV-1 never develop a cold sore.

A cold sore can be activated by a variety of factors, including:

  • Hormonal changes during menstruation or pregnancy
  • Sunburn
  • Extreme temperatures (hot or cold)
  • Stress (physical or emotional)
  • Fatigue
  • Fever and illness, such as cold or flu
  • Damaged, dry or cracked lips

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