The 'lip sore' kind is usually HSV-1 and responds to l-lysine supplementation of 3,000 mg or more per day. HSV-1 is more susceptible to lysine than HSV-2.
But 'Herp Eeze' contains lysine, prunella, and olive leaf extracts all in one capsule - that is why I use and recommend it. You can buy these separately (but they are not as easy to locate in health food stores). You will pay at least $10-$15 less per bottle online than in retail stores.
Keeping a healthy Diet and immune system is very key as well, as the virus activates easily when your defenses (immune system) are weakened.
I always suggest a good multi vitamin and checking vitamin D3 levels ( above 50 is recommended currently ). My D3 was 17 - and it took 10,000 IU daily for several mos. just to get my blood D3 up to 37. It is a common deficiency in those who do not get much outdoor exposure.
One other thing I have recently discovered creates susceptibility is exposure to toxic molds (air spores). People report outbreaks and increased illness when living or working in buildings with even small levels of such toxins (they suppress immune function).