英语时差：什么是单纯疱疹？ （下）

In fact, recurrence of these painful cold sores is very common because once you have the virus, you never get rid of it. The latent virus can be triggered by many factors. Exposure to wind and sun can cause an outbreak, and so can physical or emotional stress. Many people who have the virus get a blister every time they come down with a cold because their immune systems get overloaded and can’t attend to everything at once. Some people never get cold sores because they have never been infected with the virus, which you can get through direct contact with the lips or mouth of a person with an active sore. Researchers believe that most people were infected as children when an adult with a cold sore kissed them.