Chickenpox and shingles are caused by the Varicella-zoster virus (circular objects in upper right). The virus enters the body through epithelial tissue of the respiratory system or skin (top center). The blood stream (upper right, rear) carries the virus to sensory nerves (lower left) throughout the body. The virus migrates to the skin where it causes bumps to form, followed by blisters filled with virus. After several days the blisters scab and heal although nerve damage may remain. Inactive virus may remain gathered in the sensory nerve ganglia near the spinal cord (center right). In later life these viruses may reactivate to cause a more severe reaction called shingles.