Cold sores are red blisters full of fluid that usually appear around the lips and nose. Caused by a common viral infection, cold sores may also develop inside the mouth and can spread to the fingers. Cold sores are highly prevalent: 90 percent of the adult population carries the virus that causes them, though some people remain asymptomatic.
A type of the herpes simplex virus — HSV-1 — is usually responsible for cold sores. HSV-2 results in genital herpes, but can also cause facial sores. HSV infects more than 50 percent of Americans by the time they enter their 20s. A lot of people who have the virus never develop visible cold sores, but they can still pass the virus on. People with visible cold sores are most contagious, but the virus also spreads through close contact and shared food or cosmetics.
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