Question: how long is herpes 1 contagious?
Answer: Transmission. Share on Pinterest Cold sores may be contagious for up to 15 days. The herpes simplex virus type 1 (HSV-1) is what causes cold sores. According to the National Institutes of Health (NIH), in the United States, HSV-1 infects more than 50% of people by the time they reach their 20s.