Childhood Diseases

Updated 10 March 2016

Causes of chickenpox

Chickenpox (varicella) is a highly contagious viral disease caused by the varicella-zoster virus (VZV).


Chickenpox results when a person – usually a child but sometimes an adult – becomes infected with the varicella-zoster virus.

Following the infection, this virus spreads throughout the body, as shown by the appearance and distribution of the rash that may cover the entire body.

The virus persists

Like its relative the Herpes simplex virus, once the chickenpox illness is over, the varicella-zoster virus persists in a person for the rest of their life.

The virus remains dormant in certain nerves, usually in the spinal nerves.

Chickenpox can occur in anyone who has not had the illness before. Shingles can only occur in someone who has previously been infected with chickenpox.

The varicella-zoster virus is present in throat secretions of a person immediately before or just after developing the chickenpox rash. These secretions can reach another person as airborne droplets.

The skin blisters of chickenpox and shingles contain infectious viruses, which can reach the nose or mouth of another person by contact or touch.


Shingles (also known as "herpes zoster") is the result of reactivation of the varicella virus in one of the spinal nerves. The virus travels down the nerve, producing large blisters localised in the area that the nerve supplies.

Shingles therefore, involves an area of skin which is served by one sensory nerve. This area of skin is known as a dermatome. The dermatomes that are commonly affected during a shingles attack are those on the chest, abdomen or face. Only one dermatome is affected in a particular individual at any one time.

While shingles can occur at any age, it usually occurs in the elderly, due to the immune system’s "memory" of the virus reducing over time. The immune system may not be able to effectively control the dormant virus. Anyone whose immune system is compromised also loses the ability to control this virus.

Immune control can be reduced by stress, poor diet, immune suppression, chemotherapy treatment and in transplant patients or people with HIV infection.

Read more: 

Symptoms of chickenpox

Risk factors for chickenpox 

Diagnosing chickenpox

Revised and reviewed by Prof Eugene Weinberg, Paediatrician and Paediatric Allergist, Health24 expert, February 2015.