The weakening of the immune system as a result of aging, cancer treatments, HIV, transplant operations and stress are all potential triggers that awaken the zoster virus and lead to an outbreak of shingles, as stated by NIH Senior Health. About 95 percent of shingles cases strike adults.
The primary risk factor for developing shingles is a medical history that contains chickenpox. Of every five people who developed chickenpox earlier in life, one develops shingles, on average. The aging process robs the immune system of the ability to keep infection away, which sometimes allows the zoster virus to wake back up, according to NIH Senior Health.
People who have gone through radiation treatments for cancer (or have had cancer at all) have immune system weaknesses that make shingles more likely. People with HIV or AIDS or who have gone through a transplant operation face a similar risk. Stress does not cause shingles outbreaks all by itself, but it sometimes contributes to outbreaks in people who have gone through other triggering events. In some cases, adults who had chickenpox during their childhood and were later exposed to kids with chickenpox experienced additional immunity, which helped them stay free of shingles later on, reports NIH Senior Health.