There are three herpes virus:
Herpes simplex 1 which typically causes cold sore on lips,
Herpes simplex 2 which causes genital herpes and
Herpes zoster which causes chicken pox in both child and adults
Some infectious disease physicians may consider Epstein-Barr virus which causes glandular fever or infectious mononucleosis.
Herpes virus is a very infectious virus when it appears as blisters on skin whether it is in a form of chicken pox, cold sore or genital herpes. Therefore it is a very common infection in all age groups. Researches done in various countries showed that 90%+ people had been infected with herpes zoster, 80%+ with herpes simplex 1 and 20-30% with herpes simplex 2.
The common characteristic of all three or four herpes viruses is that once infected, the virus stays within the body for life. It is normally being suppressed by one's immune system. But when one's immune system is weaken by what ever means, the virus reactivates and outbreaks may occur as cold sores, genital blisters or shingles.