The answer to 'what causes shingles' is that shingles are caused by the varicella-zoster virus, the same virus that causes chickenpox. After you've had chickenpox, the virus remains dormant in your nerve cells. Years later, the virus can reactivate and cause a painful rash known as shingles.
Shingles typically appears as a band of blisters on one side of the body, often on the torso or face. The rash can be extremely painful, and it's important to see a doctor right away if you suspect you have shingles. Early treatment can help reduce the duration and severity of the outbreak.