Is it better to use abreva or carmex on a cold sore?

Both about same: Carmex ($) will dry the region upon which it is applied and can act as a soothing agent while shedding the outer layers of skin. Abreva ($$) is thought to act by inhibiting the fusion of the human cell with the viral envelope of the herpes virus, thus preventing its replication. It's mechanism has been questioned in a few studies. Your dentist can offer better: rx, chemical and/or laser treatment.