The virus replicates once it has penetrated the epithelial cell, then it travels to the corresponding nerve ganglion (i.e. trigeminal ganglion) via sensory nerves endings. At the nerve ganglion the virus enters a latent phase and remains dormant until it is reactivated. Reactivation can be spontaneous or stimulated by a number of factors such as: reinfection by direct effect of stimuli, immunosuppression, ultraviolet light, febrile illnesses and stress. Age: Primary herpetic gingivostomatitis is common in children from 6 months to 5 years old. This virus is also common in young adults aged around 20–25. Immune system: The prevalence and severity of the disease is dependent on the host's immune response and the virulence of the virus. Environment: As this virus is very contagious it has the potential to spread quickly in enclosed environments e.g. nurseries and orphanages. Epidemiology: Those living in developing countries are at a higher risk of HSV-1 infection. It has been reported that around a 1/3rd of children living in developing countries are HSV-1 positive by 5 years old and 70-80% of the population are infected by the age of adolescence. In developed countries only 20% of children are infected at the age of 5 and there is no significant increase in disease prevalence until 20–40 years old where the percentage of infected individuals ranges from 40-60%   Socio-economic status: Those with a lower income have a higher risk of HSV-1 infection at a younger age. Race: Studies have demonstrated that in the USA 35% of African Americans by the age of 5 have presented with the disease whereas only 18% of White Americans are affected. Herpetic gingivostomatitis originates from a primary infection of HSV-1. The series of events that take place during this infection include replication of the herpes simplex virus, cell lysis and finally, destruction of the mucosal tissue. HSV-1 can very easily enter and replicate within epidermal and dermal cells through skin or mucosal surfaces which have abrasions. This results in numerous small vesicles or blisters of up to 1-2mm on the oral mucosa, erosions on the lips, eventual hemorrhagic crusting and even ulceration, covered by a yellowish-grey pseudomembrane, surrounded by an erythematous halo.