Yes they are very contagious. I wouldn't share drinks or kiss anyone. Or even touch it then touch a different part of ur mouth cause it can spread. They usually don't last to long but sometimes they do I would say about a week or so. If u wanna get rid of it salt helps with it but there is some medicine you can buy to put on it as well. I just prefer salt it works better for me.
Yes they are, don't kiss people or perform oral sex if you have one, the herpes virus is both an STD and just a common cold sore, but one could become the other if you're not careful
Yes I can't stress enough how contagious they are!!!!