Why do we get cold sores?

Most cold sores are caused by herpes simplex virus type 1 (HSV-1). The World Health Organization estimates that around two-thirds of people under 50 worldwide carry HSV-1, though many never have symptoms. After the first infection, the virus travels up nerves and lies dormant in a nerve cluster called the trigeminal ganglion. Triggers such as stress, illness, fever, strong sunlight or hormonal changes can reactivate it, sending it back down the nerve to the lip, where it causes blisters. Antiviral creams and tablets can shorten outbreaks, but there is currently no cure.