Cold sores, or fever blisters, are a common viral infection. They are tiny, fluid-filled blisters on and around the lips. These blisters are often grouped together in patches. After the blisters break, a scab forms that can last several days. Cold sores usually heal in 2 to 3 weeks without leaving a scar. Cold sores spread from person to person by close contact, such as kissing. They're usually caused by herpes simplex virus type 1 (HSV-1), and less commonly herpes simplex virus type 2 (HSV-2). Both of these viruses can affect the mouth or genitals and can be spread by oral sex. The virus can spread even if you don't see the sores. There's no cure for cold sores, but treatment can help manage outbreaks. Prescription antiviral medicine or creams can help sores heal more quickly. And they may make future outbreaks happen less often and be shorter and less serious.