Herpes Simplex Virus 1 (HSV 1) is the virus that causes fever blisters or cold sores in humans. More than 80% of the human population are infected with this virus. Many people do not know that they are infected and may not ever have fever blisters/cold sores. HSV1 is for life- once a person is infected they remain so for life. When HSV1 is not active and replicating it lies dormant in your trigeminal nerve- one of the nerves that supplies your face. The virus is shed in fluid from fever blisters and also saliva- you don’t have to have fever blisters to be shedding the virus!! People most commonly shed the virus when they are immunocompromised, for example when sick or stressed.