So before diving into any unprotected sex etc, we have both gone and received our full STD panels, and i am completely clear. now bearing in mind she has never had an outbreak, and always tests with partners before intimacy, she was totally at a loss as to how this could happen. OK, would you dump her if she has cold sores on her lips? In fact, the vast majority of occurrences of neonatal herpes result from a baby being kissed by someone who has just contracted coldsores. If you are waiting for a first kiss or have an important social event in your near future, you may be wondering, How long is a fever blister contagious?. Cold sores or fever blisters are more often caused by the herpes 1 virus than the herpes 2 strain. A healing fever blister may scab and shed a scab several times before actually reaching complete healing. Do not share lipstick, lip gloss or lip balm with someone who has fever blisters.