Herpes zoster and chickenpox are caused by the same varicella zoster virus. After the first infection with this virus in people without or with low immunity, the clinical manifestation is chickenpox or insidious infection. In response to various triggering stimuli, the latent virus is reactivated and grows and multiplies, causing inflammation and necrosis of the invaded ganglion and producing neuralgia. At the same time, the reactivated virus can move along the peripheral nerve fibers and into the skin, where it produces the phasic blistering rash characteristic of herpes zoster. Occasionally, the virus disperses to the anterior horn cells of the spinal cord and motor nerve roots, causing muscle weakness or paralysis of the skin in the corresponding area.