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 lies dormant for years.
Eventually, it may reactivate and travel along nerve pathways to your skin — producing shingles. But, not everyone who's had chickenpox will develop shingles.
The reason for shingles is unclear. But it may be due to lowered immunity to infections as you grow 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, which includes the viruses that cause cold sores and genital herpes. Because of this, shingles is also known as herpes zoster. But the virus that causes chickenpox and shingles is not the same virus responsible for cold sores or genital herpes, a sexually transmitted infection.
Courtesy: Mayo Clinic