Cold sores - also called fever blisters - are quite different from canker sores, a condition people sometimes associate them with. Cold sores are caused by the herpes simplex virus, and they're contagious. Canker sores, which aren't contagious, are ulcers that occur in the soft tissues inside your mouth, places where cold sores don't occur.

Cold sores are common. But though you can't cure or prevent cold sores, you can take steps to reduce their frequency and to limit the duration of an occurrence.

• canker sore
• fever

Signs and symptoms

Signs and symptoms of cold sores include:

• Small, painful, fluid-filled blisters on a raised, red, painful area of your skin

• Pain or tingling, called the prodrome, often preceding the blisters by one to two days

• Usual duration of seven to 10 days

Cold sores usually appear on your lips. Occasionally, they occur on your nostrils, chin or fingers. And, although it's unusual, they may occur inside your mouth — but only on your gums or hard palate, which is the roof of your mouth. If the sore appears on other soft tissues inside your mouth, it may be a canker sore, but it's not a cold sore.

• canker sore

Symptoms may not start for as long as 20 days after exposure to the herpes simplex virus, and usually last seven to 10 days. The blisters form, break and ooze. Then a yellow crust forms and finally sloughs off to uncover pinkish skin that heals without a scar.

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