I have kissed a guy with a blister on his lip. Now I have one too. How come?

The blister on his lip might have been caused by the herpes simplex virus. This is contagious. Normally the symptoms appear several days after infection, but it can also take three weeks before you notice anything. The bad news is that once you have the virus it stays with you. The blister will disappear but it can return any time. Low resistance, sunlight, sharp spices, having your period, stress and fever can trigger it. I hope it’s not herpes but something else. See your doctor to have it checked out. For if it is herpes you should be careful not to infect someone else. That means that you should not kiss or give a guy a blow job when you gave a cold sore.