Causes of Shingles

Shingles or Herpes zoster is a reappearance of Varicella Zoster Virus that causes chicken pox. Herpes zoster is different from genital herpes that is a sexually transmitted disease. (1, 2)

How does the Varicella Zoster Virus cause Shingles?

Following the initial chicken pox infection the virus remains dormant or inactive within the nerve cells along the spine. (6)

The virus can reappear as shingles later in life often due to unknown causes. (1, 2) The virus passes down the nerve path to the surface of the skin where it causes the characteristic rash. (5)

The reactivation of the virus occurs in around one in five people who have chickenpox, and it is largely unknown why it occurs. (5)

Risk factors associated with Shingles

Although the reactivation of the virus that causes Shingles is largely as a result of unknown causes, there are several risk factors that have been associated with Shingles. These include:

  • Occurrence of chicken pox before the age of 1 (6)
  • Being under stress
  • Being over the age of 60
  • Having a weak immune system – this can be for several reasons
  • Undergoing certain cancer treatments including chemotherapy and radiotherapy
  • Taking certain medications that suppress one’s immune system, such as anti-rejection drugs following organ transplant (4)

Who does Herpes zoster affect?

Herpes zoster may affect anyone including children. However, the elderly especially those over 50 are at a higher risk.

It occurs commonly among people who have a suppressed immunity. This could be due to medications that suppress the immune system.

This is seen in patients with cancer, especially leukemia and lymphoma and those with bone marrow or solid organ (renal, cardiac, liver, and lung) transplantation.

Immunosuppressive medications include steroids, chemotherapy, or transplant-related immunosuppressive medications.

Those with immunity suppressing disease like human immunodeficiency virus or HIV AIDS may also be at risk. (1)

When does Shingles become contagious?

Shingles is not contagious until the lesions are dry and crust over.

The risk of transmission to other healthy individuals is lower if the lesions are covered.

If a person comes in contact with the rash or if the virus comes in contact with the conjunctiva or upper respiratory tract mucosa or lining, they will develop varicella infection or chicken pox rather than herpes zoster.

People at high risk of Shingles

High risk individuals include:

  • Pregnant women who have never had chickenpox or varicella vaccine,
  • Premature babies born before 28 weeks of gestation or those who weigh less than 1000 g at birth
  • Patients who have low immunity belonging to any age (1)
  • People over the age of 80 (3)

Herpes zoster may also rarely affect people who have never had chicken pox but have been vaccinated with the chicken pox vaccine. (1)

Further Reading

Last Updated: Jun 12, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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