Varicella-zoster is a virus that causes two distinct diseases: chickenpox and shingles. Chickenpox typically occurs in childhood and is characterized by an itchy rash, fever, and fatigue. It spreads easily through respiratory droplets or direct contact with the rash. After a person recovers from chickenpox, the virus remains dormant in the nervous system. Later in life, it can reactivate as shingles, leading to a painful rash and other symptoms. Vaccines are available to prevent both chickenpox and shingles, reducing the risk of infection and complications associated with these diseases.