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Shingles is not a new infection. It is the chickenpox virus (varicella-zoster) reactivating years later. After chickenpox, the virus stays dormant in your nerves for life, and it can reawaken when your immune defenses weaken — most often with age or a weakened immune system.
Shingles can feel like it comes out of nowhere — a sudden band of burning, blistering skin on one side of the body. But the virus behind it isn't new. If you've ever had chickenpox, it has been with you ever since, waiting quietly in your nervous system.
Understanding that single fact explains almost everything about who gets shingles and why. It isn't something you catch fresh, and it isn't a sign you did anything wrong. It's an old virus reactivating. Here's how that happens, who it's most likely to affect, and whether it can come back.
Shingles starts with a virus you already carry
Shingles, known medically as herpes zoster, is caused by the varicella-zoster virus (VZV) — the very same virus that causes chickenpox. The two illnesses are different chapters of one virus's story. Chickenpox is the first encounter, usually in childhood. Shingles is what can happen when that same virus stirs back to life decades later.
Here's the part most people don't realize: even after chickenpox clears and you feel completely well, the virus never fully leaves your body. Instead, it retreats and goes dormant in the nerve-root clusters (called ganglia) that sit near the spine. There it can stay, silent and harmless, for the rest of your life. Many people carry it for decades and never have a single problem.
Because shingles requires VZV to already be living in your nerves, you can only develop it if you've had chickenpox at some point — a key idea we'll come back to below.
Why the virus reactivates
So why does a virus that's been quiet for thirty or forty years suddenly wake up? The short answer is that your immune system normally keeps VZV in check, and shingles tends to appear when that check loosens.
Your body relies on a specific kind of immune defense — cell-mediated immunity — to keep the dormant virus suppressed. Over time, and especially with age or illness, that particular defense naturally weakens. When it dips low enough, VZV can reactivate: it leaves its hiding place, travels back down the length of a single nerve, and erupts at the skin as the painful, one-sided rash that defines shingles.
Shingles isn't a sign you did anything wrong. Your body has been quietly keeping this virus in check for years, and every so often it just loosens its grip for a while. That's really all it is.
— John Venzor, DO
That's why the rash follows a single nerve's path, almost always staying on one side of the body and not crossing the midline. The virus is essentially retracing the route of the very nerve it had been hiding in. If you want to know what that looks and feels like as it develops, our guide to shingles symptoms walks through it in detail.
Who's most likely to get it
Anyone who has had chickenpox can develop shingles, and the lifetime risk is substantial — roughly 1 in 3 people will get it at some point. But the odds aren't equal for everyone. The common thread among the people most likely to get shingles is simple: their immune system's ability to keep VZV suppressed has dropped, whether through the gradual changes of aging or through an illness or medication that lowers immunity. A few factors raise the risk meaningfully:
- Age — the single biggest factor. Risk rises sharply after about 50 and keeps climbing with each decade, because cell-mediated immunity naturally wanes as we get older.
- A weakened immune system. This includes cancer and the treatments used to fight it, HIV, an organ or bone-marrow transplant, and medicines that suppress immunity — such as long-term steroids and other immunosuppressing drugs.
- Major physical or emotional stress. Significant illness, surgery, or a period of intense stress is often cited as a trigger. The evidence here is weaker and less consistent than for age and immune suppression, but it's commonly described.
If you carry one or more of these risk factors, it doesn't mean shingles is inevitable — only that the odds are higher. Plenty of healthy people with no obvious trigger get shingles too, simply as a consequence of immunity quietly drifting downward over the years. It's also part of why the shingles vaccine is recommended specifically as people get older, when the natural risk begins to climb. Our guide to the shingles vaccine covers who should consider it and when.
Can you get shingles more than once?
For most people, shingles is a one-time event. Having it once appears to give the immune system a boost against the virus, which is part of why repeat episodes aren't the norm. That said, recurrences are possible — and they're more likely in people with a weakened immune system, the same group most prone to a first episode.
There's one more point worth clearing up, because it's a common source of confusion: you cannot catch shingles from another person. Shingles only happens when a virus you already carry reactivates from within. You must have had chickenpox at some point for that to be possible — or, far more rarely, carry virus left behind by the older live chickenpox vaccine.
What can spread is the virus itself, through contact with the fluid in an active shingles rash, which can cause chickenpox in someone who has never had it or been vaccinated. That's a different question from "catching shingles," and our guide on whether shingles is contagious breaks down exactly who is and isn't at risk.