Shingles is caused by the varicella-zoster virus — the same virus that causes chickenpox. Anyone who's had chickenpox may develop shingles. After you recover from chickenpox, the virus enters your nervous system and stays inactive for years.
Sometimes the virus reactivates and travels along nerve pathways to your skin — producing shingles. But not everyone who's had chickenpox will develop shingles.
The reason for shingles is unclear. It may be due to lowered immunity to infections as people get older. Shingles is more common in older adults and in people who have weakened immune systems.
Varicella-zoster is part of a group of viruses called herpes viruses. This is the same group that includes the viruses that cause cold sores and genital herpes. As a result, shingles is also known as herpes zoster. But the virus that causes chickenpox and shingles isn't the same virus that causes cold sores or genital herpes, which is a sexually transmitted infection.
https://www.mayoclinic.org/diseases-conditions/shingles/symptoms-causes/syc-20353054