Shingles (herpes zoster) is a painful condition that can occur in individuals who have experienced outbreaks of chicken pox. While the symptoms of shingles appear on the skin, its underlying causes begin deeper inside the body.
According to the National Institute of Neurological Disorders and Stroke (NINDS), shingles is a secondary eruption of varicella zoster virus, which also causes chicken pox. It begins in the aftermath of a chicken pox outbreak, when particles of varicella zoster travel from the bloodstream to nerve cell clusters called sensory ganglia, which sit near the brain and spinal cord.
Once inside the sensory ganglia, varicella zoster goes dormant and can sit inactive inside the body for many years, notes the NINDS. The reactivation of varicella zoster inside the sensory ganglia signals the start of a shingles outbreak.
Once reactivated, varicella zoster travels down nerve paths to the surface of the skin. At the skin, the virus multiplies, leading to the characteristic rash and blisters of shingles.
Although doctors are not sure what triggers varicella reactivation, the Mayo Clinic cites weakened immune system function as a potential factor.
The Mayo Clinic notes that individuals with shingles can infect others who have not had chicken pox, reinitiating the cycle leading from chicken pox and shingles.