Cold sores are most commonly painful blisters which start out as a tingling sensation around the mouth or on the lip. They are typically caused by the herpes simplex virus type 1 (HSV-1) which, once in your body, lays dormant within nerve cells before recurring as cold sores and/or genital warts. Sores on the mouth can also be caused by the herpes simplex virus type 2 as well.
Cold sores tend to heal on their own within around 10 to 14 days and are extremely contagious, but for some people, the main issue is how unsightly they can look. If you are looking for a way to help minimise the length of time your blisters last and reduce pain and discomfort as well, you can use a medicated antiviral treatment such as Valaciclovir which is designed to stop the herpes virus when it activates in the form of a cold sore.