I was talking about this the other day, as I had one last week.
I don't go when I've got one. You're not supposed to get it wet. Even in the shower if possible!
It's not good for the blister on your lip, but also, as it's highly contagious, it's not good for other people potentially!
Someone did recommend the patches - Compeed? No...I think that's for blisters! I can't remember the name. I will see if I can find the thread for you. I think they provide protection against water, but I didn't try them in the end as I didn't want to risk getting the sore wet.