Herpes or herpes simplex is a viral infection caused by herpes simplex virus type one or type two, abbreviated HSV-1 and HSV-2 respectively. The name given to the resulting condition depends upon the site of infection. Cold sores are a symptom of oral herpes which is also known as herpes labialis. Infections by HSV-1 are more common than by HSV-2 although infections by the latter strain are increasing.
Infection happens when oral mucosal tissue or broken skin in the mouth come into contact with the virus. This can be from another individual or from a different infected area. Once the infection has occurred it is there for the entire life of the individual. The virus activates to cause disease in approximately one third of people who are infected. The virus resides in the nerve tissue of the host where it is latent. Cold sore outbreaks occur when the virus reactivates and travels to the location on the face where the cold sore will develop. This latent reactivation cycle varies according to individual, how long the individual has been infected and whether the virus is HSV type 1 or type 2. Generally speaking the frequency of reactivation decreases over time and is less with HSV-2 than with HSV-1.
The viral life cycle has a predictable progression once it is activated. Prodromal symptoms include tingling and can last for a few hours to a day. The viruses start to reproduce and healthy cells react to the invasion of other cells by swelling and turning red. The pre-sore stage is followed by the painful and highly contagious open legion stage. Crusting is the next stage followed by the healing and then the post-scab stages respectively. Infection is still possible during this final stage due to shedding. Occasionally reinfections can occur inside the mouth.From the Web