Shingles is caused by the reactivation of the varicella-zoster virus, the same virus that causes chickenpox. After a person has had chickenpox, the virus remains inactive in the nerve cells of the body and can become active again many years later, resulting in shingles. The virus can reactivate due to factors such as stress, illness, aging (especially over 50 years), a weakened immune system, trauma, or treatments like radiotherapy and chemotherapy. Shingles cannot be caught from someone who has shingles, but a person who has never had chickenpox or the chickenpox vaccine can get chickenpox from someone with shingles through direct contact with the fluid from shingles blisters. The rash usually appears on one side of the body along nerve pathways and is often painful and blistering.