Shingles, also known as herpes zoster, is caused by the reactivation of the varicella-zoster virus (VZV) in people who have previously had chickenpox. After a person recovers from chickenpox, the virus can remain dormant in the nerve cells near the spinal cord and reactivate later in life, causing shingles.
It’s not clear why the virus reactivates, but it’s thought to be related to a weakened immune system due to aging, stress, illness, or medications that suppress the immune system. Shingles typically develops in people over the age of 50, but it can occur at any age.
