What causes fever blisters/ cold sores on my upper lip?!?

Cold sores. Cold sores/fever blisters are cause by the herpes simplex virus. There are 2 types—oral & genital. Either type can cause a "cold sore" although the oral type is usually involved with lip lesions. There are several otc treatments to lessen symptoms, but prescription anti-viral meds work better to clear the lesions. Herpes, however, is not cured; it is suppressed & can reappear.—>.
Herpes simplex virus. It is very common virus everybody is expossed once upon the time in life. Outbreak may happen for variety of reasons ( fever, exhaustion, period in woman, etc... Most efective treatemnt is oral anitviral medication ( it is a prescription) .