Herpes genitalis (or genital herpes) is a genital infection caused by the herpes simplex virus (HSV). A 1998 study indicated it was the most common sexually transmitted infection by the number of cases. Most individuals carrying herpes are unaware they have been infected and many will never suffer an outbreak, which involves blisters similar to cold sores. While there is no cure for herpes, over time symptoms are increasingly mild and outbreaks are decreasingly frequent.