Shingles: Causes and Risk Factors

Shingles occurs when the varicella-zoster virus (VZV), the same virus that causes chickenpox, reactivates. Why the virus re-emerges isn’t entirely understood, but there are theories. 

Shingles is most common in older people, but anyone with the varicella-zoster virus is at risk. In fact, reduced immunity is considered the biggest risk factor for shingles. Stress could also play a role for some people.

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 being a condition known as postherpetic neuralgia (PHN).

PHN is characterized by a burning sensation where the shingles rash once was. That’s why it’s important to understand what causes shingles, what the risk factors are, and how to protect yourself.

Shingles Causes

After recovering from chickenpox, the symptoms disappear, but VZV retreats to cells in the nervous system, where it can remain for decades without causing problems.

It’s not entirely understood what prompts VZV to reactivate and cause shingles. 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 VZV would behave similarly.

The big difference is that while herpes infections can recur multiple times, most people only experience shingles once (although it can come back).

The viral reactivation seems to have two main causes: a weakened immune system and stress.

Weakened Immune System

There is a clear association between shingles and weakened immunity to infection. Even though VZV is not invading the body for the first time, the immune system still is responsible for keeping it at bay.

People with weakened immune systems are at higher risk of getting shingles. Your immune system naturally weakens with age, which is why the risk of shingles increases with age. The majority of people who develop shingles are 50 years and older.

Stress

There’s some controversy surrounding the association between stress and shingles. Some studies reveal that stress causes the shingles virus to reactivate. Specifically, research shows that long-term stress increases inflammation and weakens the immune system.

Because stress weakens the immune system, and a weakened immune system is a risk factor for shingles, some experts believe that stress indirectly triggers shingles. A 2018 study found that perceived mental stress, negative life events, and a low sense of purpose may contribute to the development of shingles.

Some researchers find no link between the two conditions.

More research needs to be done to understand the connection (or lack thereof) between shingles and stress.

Shingles Risk Factors

Since compromised immunity is the most common trigger for a latent varicella virus to become active, any factor associated with a weakened immune system can increase the risk of shingles. Important risk factors for shingles include:

• Being 50 or over: With age, there is a natural decline in cell-mediated immunity.
• Infection from human immunodeficiency virus (HIV): Although most people who develop shingles have the infection just once, someone with HIV may have recurrent shingles infections.
• A chronic medical condition: Cancer (especially leukemia or lymphoma) or diabetes are examples.
• Medication that suppresses the immune system: Some examples of these include chemotherapy drugs and systemic steroids, such as prednisone.
• Having an organ transplant: The medications that are necessary for preventing organ rejection suppress the immune response. 

Note that many of these risk factors are as likely to apply to young people and 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.

Virus Reactivation and Symptoms

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, which 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.

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).

Along with the rash, symptoms of shingles may include:

• Fever
• Chills
• Headache
• Upset stomach

For several days before the rash appears, you may have tingling, itching, or pain in the affected area.

Prevention

Shingles is best prevented with a vaccine. Called Shingrix, this vaccine is considered safe and 90% effective at preventing the disease. It’s given in two doses and is available in medical offices and some pharmacies.

You should get the shingles vaccine if:

• You’re over 50
• You’ve had chickenpox, the chickenpox vaccine, or shingles
• You haven’t had chickenpox
• You got the prior shingles vaccine (Zostavax)

Avoidance is an important part of prevention, too. If you haven’t had chickenpox or a chickenpox vaccine:

• Avoid people who have chickenpox so you don’t catch it.
• Avoid people who have shingles. You could catch chickenpox (but not shingles) from them.