The Crimson Head is one possible mutation a zombie can experience, depending on the strain of t-Virus it is infected with. The V-ACT process is responsible for its crimson skin, earning it its name.
The Crimson Heads and Lickers trace their existence to a mutant t-Virus strain being worked on at the Arklay Laboratory. The result of the mutation in a human test subject created the Crimson Head Prototype 1. While it was too dangerous to be further examined at the laboratory, samples of the virus strain were obtained after its capture. This strain of the virus was being worked on at the laboratory when the biohazard occurred, leading to the generation of new Crimson Heads.