Why do cold sores always blister?

Location of virus: Herpes outbreaks (cold sores) create viral inclusion bodies in the outer layer of skin (the epidermis). The presence of these viral inclusion bodies disrupts the normal architecture of the epidermis, allowing for the formation of blisters.

Herpes: Viruses exhibit rapid rates of mutation which can make immunity difficult to sustain, especially considering chemical drugs for herpes contain only a single antiviral agent. Once a cell is infected it is difficult to selectively inhibit the virus without harming the host cell. As a result, much interest has focused on plants as strong allies in restoring immune strength.