Commonly Abused Drugs · Taking Meds When Pregnant 27, -- Here's good news for cold sore sufferers. While most people are exposed to the virus, it's not known why some people get cold sores while others do not. People who have the highly contagious sores are advised not to kiss anyone. Cold sores are caused by a viral infection called herpes simplex Over time, subsequent outbreaks usually lessen in severity and take less time to heal. cold sore are when the blisters begin to show up and after they burst. Like all forms of the herpes simplex virus, cold sores are highly contagious. Kissing and cold sores is risky business, because if you kiss someone while you Still, it's important to take precautions to prevent cold sores from spreading, even if valacyclovir to treat cold sores, from the medication's mechanism of action in the.