system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are you susceptible to getting shingles if you've had chickenpox?

I've had shingles, and it was a nightmare. I was also one of those kids who was part of a "chickenpox party" growing up. 

I have heard people say that you need to have had chickenpox to develop shingles later. Is this true?
gpt
Yes. Both are caused by the same virus (varicella herpes zoster). The first time you get infected, it manifests as chickenpox. Since the virus is now in your body, the next flare up, sometimes decades later, manifests differently, as shingles. The virus remains in the nerve cells and once it reactivates it travels to the ends of nerve cells inside skin and causes the painful localized rash and blisters typical of shingles. People who have not had chickenpox might get infected in contact with people who have active shingles.