A risk factor for shingles is having had chickenpox before 18 months of age.
Shingles is caused by the varicella zoster virus (VZV) that also causes chickenpox
 During an outbreak of shingles, exposure to the varicella virus found in shingles blisters can cause chickenpox in someone who has not yet had chickenpox, although that person will not suffer from shingles, at least on the first infection

