Cold Sores ,at what stage are they contagious?

A friend of mine often has cold sores on her upper lip, she has a habit of always greeting everyone with a quick mouth to mouth greeting, at what stage is the cold sore contagious ? she gave me a quick peck before I realized she had one at the time, does that mean I now have the herpes virus ? or it it only... show more A friend of mine often has cold sores on her upper lip, she has a habit of always greeting everyone with a quick mouth to mouth greeting, at what stage is the cold sore contagious ? she gave me a quick peck before I realized she had one at the time, does that mean I now have the herpes virus ? or it it only contagious if my skin is broken on the lip? please give well informed answer as our other friends are also worried about this habit
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