Shingles is triggered when the chickenpox virus, which stays dormant in your nerve cells after your initial infection, reactivates due to a weakened immune system. The most common triggers include psychological stress, aging, certain medications, physical trauma, and diseases that compromise immune function. About one in three adults who had chickenpox will eventually develop shingles, and understanding what sets it off can help you reduce your risk.
How the Virus Reactivates
After you recover from chickenpox, the varicella-zoster virus doesn’t leave your body. It retreats into clusters of nerve cells near your spinal cord and brain, where it can remain silent for decades. Your immune system actively keeps it in check during that time, maintaining a kind of standoff.
When something disrupts that immune surveillance, the virus begins replicating again inside the nerve cluster. It then travels along nerve fibers to the skin, which is why shingles appears as a painful, blistering rash in a band or strip on one side of the body. The pattern follows the path of the specific nerve where the virus reactivated. In some cases, the virus spreads within the nerve cluster before traveling outward, which can produce more extensive skin lesions.
Stress and the Immune System
Stress is one of the most frequently cited triggers, and there’s a clear biological reason. When you’re under significant stress, your body releases cortisol as part of its fight-or-flight response. Cortisol directly suppresses immune function, which can create an opening for the dormant virus to reactivate.
This isn’t limited to emotional stress. Any event that places major demands on your body counts: a serious illness, surgery, grief, prolonged sleep deprivation, or intense physical exhaustion. Researchers have also noted that the surge in shingles cases among people with COVID-19 likely reflects the combined effect of psychological and immunological stress working together to weaken the body’s viral defenses.
Short-term, everyday stress probably isn’t enough to trigger an outbreak. The kind of stress linked to shingles tends to be prolonged or severe, the type that leaves you feeling run down for weeks.
Aging
Age is the single biggest risk factor. Your immune system naturally becomes less effective as you get older, a process called immunosenescence. The specific branch of immunity responsible for keeping varicella-zoster in check gradually weakens, which is why shingles becomes dramatically more common after age 50. The risk continues climbing with each decade. Most people who develop shingles are over 60.
Medical Conditions That Weaken Immunity
Certain diseases significantly raise your risk by directly impairing immune function. According to the American Academy of Dermatology, the conditions most strongly associated with shingles reactivation include:
- Blood cancers like leukemia and lymphoma, which disrupt the immune cells that normally suppress the virus
- HIV, which progressively destroys the immune cells the body relies on to keep dormant infections contained
- Autoimmune conditions requiring immunosuppressive treatment, such as severe psoriasis or psoriatic arthritis
- Organ transplants, which require lifelong medications to prevent rejection, at the cost of broad immune suppression
Any condition that compromises your immune system, even temporarily, can create a window for the virus to reactivate. This includes severe infections unrelated to shingles, which can divert immune resources and leave the virus less closely monitored.
Medications That Raise Your Risk
Several classes of drugs suppress the immune system enough to trigger shingles. The most common culprits are chemotherapy drugs, which broadly reduce immune cell counts, and medications taken after organ transplantation. Biologic therapies used for autoimmune diseases also carry risk, particularly those that target B cells (a type of immune cell involved in fighting infections). The CDC specifically recommends that patients receiving these treatments get vaccinated before starting therapy when possible, because the drugs reduce the body’s ability to keep the virus dormant.
Long-term use of oral corticosteroids, often prescribed for conditions like severe asthma, inflammatory bowel disease, or lupus, also suppresses immune function in a way that mirrors what stress hormones do naturally. If you’re on any of these medications, your doctor has likely already discussed your elevated risk.
Physical Injury and Trauma
Physical trauma can trigger shingles, sometimes at or near the injury site. Broken bones, surgical procedures, and head injuries have all been linked to outbreaks. The connection makes sense: major physical injury creates systemic stress, floods the body with cortisol, and diverts immune resources toward healing.
Head trauma appears to carry a particularly notable risk in older adults. Researchers have found that older people who experience head injuries are more likely to develop shingles afterward than younger people with similar injuries, possibly because their already-declining immune systems are less able to absorb the additional strain.
Can You Get Shingles More Than Once?
Most people only develop shingles once, but recurrence is possible. Estimates range from about 1% to nearly 10% of people experiencing a second episode. Your risk of recurrence is higher if your first episode was severe, if you have an ongoing condition that weakens your immune system, or if you’re older. The same triggers that caused the first outbreak can cause another one.
Vaccination as Prevention
The recombinant zoster vaccine (sold as Shingrix) is the most effective tool for preventing shingles. It works by training your immune system to recognize and suppress the virus more effectively, essentially reinforcing the barrier that keeps it dormant. In clinical trials, the vaccine showed roughly 87% efficacy in adults with blood cancers and about 68% efficacy in people who had undergone stem cell transplants, two groups at especially high risk. Efficacy is even higher in healthy older adults.
The vaccine is recommended for adults 50 and older, and for immunocompromised adults 19 and older. It’s given as two doses, spaced two to six months apart. Even if you’ve already had shingles, vaccination can reduce the chance of it happening again. If you’re scheduled to begin chemotherapy, biologic therapy, or another immunosuppressive treatment, getting vaccinated beforehand provides the strongest protection.