Causes and Risk Factors of Shingles

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Shingles is caused by reactivation of the varicella virus, which when it first infects the body causes chickenpox but then goes into "hiding" in the nervous system. Why the virus re-emerges isn't entirely understood, but there are theories.

Shingles is most common in older people, for example, probably because the immune system becomes weaker with age.

In fact, a compromised immune system is largely regarded as the biggest risk factor for shingles. This means that even young people and children with certain conditions or who take medications that affect the immune response can be at risk for the disease. Researchers believe that for some people stress could play a role.

Shingles is an especially unpleasant illness. It causes a painful and unsightly skin rash, as well as potential long-term complications. The most common one, a condition known as postherpetic neuralgia (PHN), is characterized by a burning sensation in the area where the shingle rash was. That's why it's important to understand what causes chickenpox, who's most at risk of coming down with it, and how to protect yourself if you're exposed.

Reactivation of the Varicella Virus

After a person recovers from chickenpox, the symptoms disappear but the varicella virus that caused it retreats to cells in the nervous system, where it can hang out for decades without causing problems.

When the virus re-emerges, it typically reactivates in clusters of nerve cells in the peripheral nervous system called a sensory ganglion. The ganglia most likely to host varicella are those in the cervical, thoracic, and lumbar spine. Varicella also often affects the trigeminal ganglion that provides sensation to the face.

As its name suggests, this particular clump of nerves has three branches. The one associated with eye function, the ophthalmic branch, is 20 times more likely than the other two to be affected.

The body part associated with the particular nerve cells in which the virus reawakens is where the shingles symptoms—extreme pain, unsightly rash—will be concentrated. Since the nervous system consists of tree-like branches of nerves, the blisters will follow the particular path of the nerves affected. That's why a shingles rash often resembles a swath of blisters in a very specific area, rather than spread all over the body (as in chickenpox).

Common Causes

What prompts the varicella virus to reactivate isn't entirely understood. The virus is a member of the same family of microbes that cause herpes infections, such as genital herpes and cold sores, which also tend to come and go, so it's not surprising that varicella would behave similarly. The big difference is, while herpes infections can recur multiple times, most people only experience shingles once. In any event, there are two main causes of shingles:

Weakened immune system

There is a clear association between shingles and weakened immunity to infection.

Even though the varicella virus is not invading the body for the first time, the immune system still is responsible for keeping it at bay. It's when the immune system isn't strong enough to do this that the virus may take the opportunity to wreak havoc. This puts certain groups of people at higher risk than others of developing shingles, including those who are:

  • Ill with a chronic condition such as cancer (especially leukemia or lymphoma) or diabetes
  • On medication that suppresses the immune system. Some examples of these include systemic steroids such as prednisone,  chemotherapy drugs
  • Taking immunosuppressive medications because of an organ transplant

Note that many of these risk factors are as likely to apply to young people and even children as they are to older people. So even though shingles often is regarded as an illness of advancing age, this isn't always the case.


There's a long-held hypothesis that chronic stress or even a single episode of emotional distress can trigger the dormant varicella virus to become active again and bring on a shingles outbreak. Given that stress often is linked to any number of changes in health, including gastrointestinal problems, migraines, and eczema, this notion is not at all far-fetched.

In fact, there is some evidence to support it. For example, an often cited study conducted in 1998 of otherwise healthy adults over 60 found that those who'd had shingles were more than twice as likely to have had a negative life event within six months of the outbreak. When asked about events within the past two to three months, those in the same group were not able to report any more or less negative events than their unaffected counterparts, suggesting that the perception of a recent event as stressful, rather than the event itself, was linked to the increased rate of shingles.

More recent research has largely supported this concept. Some have taken this to mean that the overall perception of stress and the ability to cope with it, may add to the underlying factors that create the perfect storm for a shingles outbreak.

A 2003 study aimed to determine whether Tai Chi, when used as a stress reduction tool, had any bearing on the incidence of shingles in older adults. While small, the researchers were able to report that a 15-week course of Tai Chi, practiced for 45 minutes three times a week, was associated with an increase in the cell-mediated immunity specific to varicella virus.

While the investigators were unable to correlate this to a reduction in shingles risk, the study suggested that the very practice of stress reduction can yield beneficial physiological changes to adults at risk of stress-related illnesses.


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