The chance of spreading herpes when a cold sore is dried up is small. When it's not visible altogether, it's smaller still. Many millions of people have cold sores--it isn't possible to go through the rest of one's life without kissing other people. The risk is low, even if not zero. This refers to spread anywhere--lips or genitals. You should level with your new partners, but it's hardly a point of shame to have a cold sore.
Take care.
Dr. Rockoff
Therefore, I would ALWAYS advise that you wait until at least 5/7 days AFTER it has fully healed and gone before considering yourself no longer infectious. Also, if you get the slightest idea that a cold sore is on it's way then refrain from ANY skin to skin contact with the infected area. The herpes virus will invade the body through the most miniscule of tears in the skin.
Hope this helps.
Angi