Your health professional can diagnose cold sores by asking questions to determine whether you've been exposed to the herpes simplex virus (HSV) and by examining you. No further testing is usually needed.

There are two types of herpes simplex virus: HSV-1 and HSV-2. Both virus types can cause lip and mouth sores (herpes labialis) and genital herpes if your skin comes into contact with either type.

If it is not clear that you have cold sores, herpes tests may be done. The health professional takes a sample of fluid from a sore and has it tested. Having the sample taken is usually not uncomfortable even if the sore is tender or painful.