Herpes simplex labialis is among the most common skin infections and affects more or less 95% of the population.

Lip herpes (also known as cold sore) is a viral infection which is provoked by the Type 1 Herpes-simplex virus. Transmission takes place by way of droplet infection, through direct contact, or as a smear infection. Most of the affected persons have contracted the virus very early in their childhood. However, the infection doesn't by any means manifest itself in everyone. It takes two to twelve days from the time of contraction to the outbreak of the infection. The invading viruses attack the most superficial cells of the skin and travel over the sensory nerves to the respective ganglia where they engender an infection of these nerves. During the first week, the virus in the mucous membrane as well as in part of the infected nerve cells is eliminated. The virus can, however, linger in the surviving nerves, unrecognizable and therefore unattackable by the immune system. These surviving cells serve as a life-long virus reservoir. Whenever the immune system of the infected person is weakened, a reinfection occurs.

The virus then spreads along the nerve pathways in the opposite direction towards the skin surface. Causative agents include exposure to the suns rays, injuries, burns, or systematic causes such as stress, fever, menstruation, and tumorous diseases. The first symptoms of lip herpes are prickly sensations, burns, itchiness and a feeling of tightness; occasionally pain as well. Shortly thereafter, small, liquidfilled blisters appear. These burst after a few hours or days, dry out, and leave behind scabs which heal by themselves after about 7-10 days.

The entire cycle of the herpes reactivation normally takes between 10 and 14 days. The affected skin and mucous membrane areas are highly stressed during the various stages which run their course during the out-break of the blisters - blister formation (vesicle phase), wounds (ulceration phase), scab formation and healing.