My younger sister keeps getting cold sores on her lips. they will appear for a few days, then comes back weeks later what could this mean?

Cold Sores: Cold sores are a herpes infection. You get such an infection from direct contact, such as kissing. Usually there is tingling of the skin followed by blisters which dry up, can scab, and then heal. Rarely, scarring may result. Unfortunately, there is no cure and the virus lives in the nerves forever. Therefore, the sores may come back--usually when under stress or there is sunburn.