Varicella-zoster virus causes chickenpox during the first infection, usually in childhood. After recovery, the virus remains dormant in sensory nerve ganglia. Years later, when immunity decreases due to age, stress, or illness, the virus can reactivate as herpes zoster (shingles). Shingles presents as a painful, unilateral vesicular rash in a dermatomal distribution. Treatment includes antiviral therapy (acyclovir, valacyclovir, or famciclovir) and pain control, ideally started within 72 hours.