Causes of cold sores

Cold sores are usually caused by the herpes simplex virus. In most cases the virus is passed on in early childhoodfor example, when a child is kissed by a family member or friend with a cold sore. The virus passes through the skin and travels up the nerves, where it lies inactive (dormant) until it's triggered at a later date. Cold sore triggers Factors thought to trigger outbreaks of cold sores include: having another infection, such as a RTIs (respiratory tract infections) having a high temperature (fever) emotional upset or psychological stress tiredness and fatigue an injury to the affected area menstruation (periods) strong sunlight However, in many cases there's no obvious trigger for an outbreak. Genital herpes Cold sores can happen after having oral sex with a man or woman who has genital herpes .